Title of Invention

AN IMPROVED PROCESS OF PREPARATION OF BLOCK COPOLYMERS AND THE BLOCK COPOLYMERS PREPARED THEREFROM

Abstract

The present invention relates to a process of preparing a block copolymer and the block copolymer prepared therefrom comprising of at least two types homoblocks, all belonging to the polysulfone family, wherein each of the said homoblock has an identical or different molecular weight of at least 1000 and has at least 5% of the overall weight and wherein the block copolymer has a molecular weight of at least 2000,the process steps comprising of preparing each of the aforesaid homoblocks by reacting at least one aromatic diol with at least one aromatic dihalo compound, one of which contains at least one sulfone group, in at least one aprotic solvent in the presence of at least one alkali, optionally in the presence of a first azeotropic agent and the reacting the aforesaid homoblocks together in at least an aprotic solvent, optionally followed by end-capping said block copolymer.

Full Text

FORM 2 THE PATENTS ACT 1970 (39 of 19 70) COMPLETE SPECIFICATION (SECTION-10; RULE 13) " AN IMPROVED PROCESS OF PREPARATION OF BLOCK COPOLYMERS AND THE BLOCK COPOLYMERS PREPARED THEREFROM " GHARDA CHEMICALS LTD., AN INDIAN COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, HAVING ITS REGISTERED OFFICE AT 5/6, JER MANSION, 10, W.P. VARDE MARG, OFF TURNER ROAD, BANDRA (W), MUMBAI-400 050, MAHARASHTRA, INDIA. &* FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THIS INVENTION AND THE MANNER IN WHICH FT IS TO BE PERFORMED: FIELD OF THE INVENTION The present invention relates to a process of preparing a block copolymer from a family of polysulfones and to the block copolymer prepared therefrom. Furthermore, the present invention relates to di- and tri-blocks as well as random multi-block copolymers and the process of their preparation. These homoblocks may have varying molecular weights or may have similar molecular weights as compared to their original molecular weights, when present in block copolymers. These block copolymers show a single glass transition temperature (Tg), good transparency and can be readily processed using traditional plastics processing techniques. They can be used directly for molding, extrusion and also used as a compatibilizer for their high molecular weight homologues. BACKGROUND OF THE INVENTION The family of polysulfone polymers is well known in the art and three types of polysulfone have been available commercially viz. Polysulfone (PSU), Polyether Sulfone (PES) and Polyphenylene Sulfone (PPSU). The commercially available Polysulfones (PSU, PPSU, PES) have good high temperature resistance and generally do not degrade or discolor at their processing temperatures of 350°C to 400°C. Additionally, they are transparent, light amber colored amorphous plastics with excellent mechanical and electrical 2 properties, and good chemical and flame resistance. These Polysulfones are readily processible using common plastics processing techniques such as injection molding, compression molding, blow molding and extrusion. This makes them very versatile and useful plastics, having a myriad of applications in electronics, the electrical industry, medicine, general engineering, food processing and other industries. The Polysulfone PSU was discovered in early 1960 at Union Carbide (U.S. Patent No. 4,108,837, 1978). Since then, activity in improving the quality of PSU has remained strong and improvements are sought continuously over the years in color, thermal stability, molecular weights and reduction in residual monomer and solvent. While, there are many similarities among PSU, PES, and PPSU as regards color, electrical properties, chemical resistance, flame resistance etc., there are also important differences. The foremost difference among these is the Glass Transition Temperature (Tg). PSU has a Tg of 189°C, PES has a Tg of 225°C, while PPSU has a Tg of 222°C. Thus, PSU has an overall lower thermal resistance in terms of its dimensional stability compared to PPSU and especially PES, which has the highest thermal resistance. Besides this, PES also has a higher tensile strength (> 90 MPa) compared to PSU and PPSU (both 70-75 MPa). On the other hand, PPSU has an outstanding impact resistance, like Polycarbonate (PC) and its Izod notched impact strength is 670-700 J/m. Both PES and PSU have lower Izod notched impact strengths of only 50-55 J/m. Similarly, it is known in the art that articles 3 made from PPSU can withstand >1000 sterilization cycles without crazing, while PSU based articles withstand about 80 cycles and PES based articles withstand only about 100 cycles. PSU, on the other hand, has the lightest color and can be more readily processed, while PPSU is darker and more difficult to process than either PSU or PES Thus, a combination of PSU properties such as easy processibiMty and light color properties with PPSU properties such as high temperature and impact resistance would be desirable. Incorporating a proportion of PSU into PPSU may also bring down the overall cost. Although the physical blending of PPSU and PSU is one way of accomplishing this, it destroys one of the most important properties of the two homopolymers, namely their transparency. Similarly, physical blend of PES and PSU is not only opaque but also not processible to give blends of desirable properties, as they are very incompatible polymers. Other combinations as given below are also desirable for their having higher Tg than Tg of PES to further boost the high temperature resistance by incorporating these and to make the high temperature resistant polymers more readily processible by incorporating PES, PSU or PPSU in their chain structures. The unit chain structures of the part of family of polysulfones are given below: PPSU: 4 The polvsulfones are prepared using one or more aromatic Dihalo compound like Dichlorodiphenyl sulfone (DCDPS) or Dichlorodiphenyl disulfbnylbiphenyl (CSB) and one or more of aromatic di-hydroxy monomer like Bisphenol A, Dihvdroxv diphenvlsulfone (DHDPS), Biphenol, Dihvdroxv diphenyl ether, Dihydroxy diphenyl methane, their respective mono, di or tetra substituted Methyl derivatives, etc. For PPSU, the di-hydroxy compound used is Biphenol (H0-C6h4-G6H4-OH), for PES, it is DHDPS and for PSU, it is Bisphenol A (HO-C6H4-C(CH3)2-C6H4-OH), while DCDPS is used as a second monomer for all these three commercially available polysulfones. The use of more than one dihydroxy monomers is also known. For example, the polymer known as "PAS" manufactured by Amoco includes a small quantity of hydroquinone in addition to DCDPS and DHDPS. The third monomer is added at the start of the manufacturing process and so gets polymerized in a random sequence in the polymer chain. 5 Other random copolymers in the prior art have shown that a third monomer may also be added in much larger quantities. Thus, GB Patent 4, 331, 798 (1982) and US patent 5, 326, 834 (1994) teach the preparation of terpolymers using 80-40 mole % of DHDPS and correspondingly 20-60 mole % of Biphenol with near equivalent mole % of DCDPS. Since both patents teach that polymerization is to be started with the monomers themselves, it can be seen that the distribution of DHDPS and Biphenol in the final copolymer will be at random. Thus, one gets a random sequence such as: --ABAABBBAABAAABBABABBAAABB--, where A and B are present in a random sequence and in variable amounts depending upon the initial concentrations of A and B or DHDPS and Biphenol. (DCDPS moiety will be present in between A-A, A-B & B-B groups, although not shown here). Similarly, European Patent No. 0,331,492 teaches the synthesis of random terpolymers of DCDPS and DHDPS/Biphenol or Bisphenol A/Biphenol. Again, starting from three monomers to give random terpolymers (and not block copolymers) by building up molecular weights, in which the sequence of A & B in the chains, being random, cannot be predicted. The prior art shows that block copolymers have been prepared where only one of the blocks is polysulfone. Hedtmann-Rein and Heinz (US Patent 5, 036, 146 -1991) teach the preparation of a block copolymer of PSU with a polyimide (PI). In this case, a homoblock of an amine terminated polysulfone was prepared first. This was preformed using DCDPS, Bisphenol A and p-aminophenol to give a homoblock having a molecular weight in the range of 1500 to 20000. The homoblock produced was subsequently reacted with a tetracarboxylic acid, such as 6 benzophenonetetracarboxyiic dianhydride, and another diamine, such as 4,4"-diaminodiphenylmethane, to make a block copolymer of PSU-PI The copolymers were prepared in the melt phase at 350°C. McGrath and coworkers (Polymer preprints, 25, 14, 1984) have prepared PSU-Polyterphthalate copolymers. This was done using DCDPS (0.141 mole) and a mixture of hydroquinone and biphenol (0.075 mole each) to give a homoblock in solution, and then reacting the homoblock with a terephthaloyl chloride and biphenol, using solution or interfacial techniques, to give a block copolymer. McGrath et al (Polymer Preprints, 26, 275, 1985) have further described preparations using acetyl end capped PSU with p- acetoxy benzoic acid or biphenol diacetate/terephthlic acid to obtain block copolymers of PSU/Polyethers, the latter part being highly crystalline or even liquid crystalBhe polymers. The synthesis of the block copolymer was carried out as a melt or in the presence of diphenyl sulfone at 200 - 300°C. Block copolymer preparation was indicated by the fact that the product was not soluble in common organic solvents. McGrath and coworkers (Polymer Preprints, 26, 277, 1985) have also developed block copolymers of PSU and PEEK using a hydroxy terminated oligomeric PSU homoblock and difluoro benzophenone alone or optionally adding hydroquinone and/or biphenol. The first method, rather than giving a block copolymer, gives PSU blocks joined by difluorobenzophenone. However, the 7 second method has the possibility of producing both random and block structures in the copolymers of PSU and PEEK. While the above investigations have prepared PSU block copolymers, it can be seen that most have opted for the combination of hydroxy terminated PSU with other monomers, which on polymerization give block copolymers. In this process, it is quite likely that the polymerizing monomers would give block sizes so varied that some of the PSU blocks may be joined by nothing more than a single monomer unit having a molecular weight of only 300 or less, and certainly 1000 to be called a block. Thus, depending on the concentration, it is likely that the second homoblock will be no more than a single or double monomer unit. Such a situation can be averted by preparing the two homoblocks separately and reacting them to give a block copolymer. Noshay and coworkers (J. Polymer Sci. A-J, 3147, 1971) have prepared block copolymers of amine terminated dimethyl Siloxanes and hydroxy terminated PSU. The hydroxy terminated PSU was prepared using a slight excess of Bisphenol A (0.495 mole) over DCDPS (0.450 mole). The -ONa groups were then converted to -OH groups using oxalic acid and the product was precipitated. The dried PSU powder was reacted with a separately prepared amine terminated polysiloxane in ether at 60°C. It may be noted that while PSU is plastic, Polysiloxane is elastomeric and hence the combination gives a block copolymer with thermoplastic elastomer like properties. 8 Surprisingly however, there has been no described method, nor synthesis carried out, whereby two Sulfone homoblocks have been used to form a block copolymer with thermoplastic properties. The usual method of preparation of these polysulfones consists of the following process: An aprotic organic solvent selected from Sulfolane, N-methyl pyrrolidone (NMP), Dimethyl Acetamide (DMAe), Diphenyl sulfone, Dimethyl sulfone or Dimethyl sulfoxide (DMSO), usually distilled over an alkali, is placed in the reactor. DCDPS or similar dihalo monomer and the second dihydroxy monomer (Bisphenol A or Biphenol, etc.), generally in the near mole proportion 1.00:1.00, are added to this reactor along with sodium or potassium carbonate. Toluene or monocWorobenzene (MCB) is added to facilitate dehydration. The temperature of the mixture is then slowly increased to from 140°C to 170°C depending on the solvent utilized, whereupon the alkaline carbonate reacts with the phenol to give a salt and liberate water. The water gets distilled off, which is facilitated by toluene or MCB, if present. The reaction mixture after water removal is then heated to a temperature in the range of 170°C to 230°C, depending on the solvent, alkali and the dihydroxy monomer used, until the desired viscosity or molecular weight is attained. Thereafter, the growing chains are end-capped with MeCl and the reaction mass is 9 filtered to remove salt and then polymer chains are precipitated in water or MeOH, further treated to remove the residual solvent, and dried. Alternately, solvent may be flashed off and reaction mass may be passed through a devolatizing extrader directly to remove residual solvent and for polymer granulation. Adding more than one hydroxy monomer to the above leads to ter-copolymers with three, instead of two, monomer units incorporated randomly in the chains. It is desirable that a method of block copolymer formation is evolved whereby two plastics, both of which are sulfone-based oligomers, are connected to form a single chain as a block copolymer. As noted earlier, block copolymers of different polysulfones are not known in the art. In general, as known in art, three requirements need to be met for the successful formation of block copolymers from homoblocks: i) The two homoblocks should have end groups that react with each other, i.e. -OH&-CNO ii) Each homoblock should have identical end groups i.e. -OH or -CNO. iii) The two homoblocks should be mixed in exact stoichiometric proportions to give high molecular weights. 10 The present invention discloses a process of preparing block copolymers using two or more different polysulfbnes homoblocks and the strict requirement of each homoblock having exactly similar end groups is avoided. Similarly, the exact stoichiometry for two or more homoblocks can be avoided for high molecular weight block polymer formation. SUMMARY OF THE INVENTION The present invention relates to a process of preparing a block copolymer comprising of at least two types of homoblocks, all belonging to the polysulfone family, wherein each of the said homoblock has an identical or different molecular weight of at least 1000 and has at least 5% of the overall weight and wherein the block copolymer has a molecular weight of at least 2000, the process steps comprising of: (a) preparing each of the aforesaid homoblocks by heating at least one aromatic diol with at least one aromatic dihalo compound, one of which contains at least one sulfone group, in the presence of at least one alkali optionally in at least one solvent and further optionally in the presence of an azeotropic agent, (b) reacting the aforesaid homoblocks together optionally in at least a solvent, and further optionally followed by end-capping said block copolymer, (c) recovering the block copolymer. 11 The present invention also relates to the block copolymers prepared using the aforesaid process. The present invention describes the preparation of block copolymers of various types of polysulfones. These novel block copolymers are prepared using a technique whereby lower molecular weight homoblocks are first separately prepared and then mixed in different proportions and reacted further to give high molecular weight block copolymers. It becomes possible, using this technique, to ensure the formation of the block structures, as well as their sequences and the block molecular weights. Besides segmented multi-blocks copolymers, even high molecular weight di-blocks or tri- blocks as well as multi-blocks with known block molecular weights are feasible using this method. Block copolymers thus prepared find usage as novel poiysulfone plastics, and also as compatibilizers. DESCRIPTION OF THE INVENTION In general, two possible chain end structures exist on a polymeric chain of a homoblock of a poiysulfone. These end groups are -CI, emanating from a dihalo, (DCDPS) moiety and -OH emanating from the Phenolic monomer. A mixture of the both end groups is also possible for a given polymeric chain. For block copolymers, one expects, based on prior art, that the one homoblock should have only two -CI end groups per chain and the second homoblock should have only two -OH end groups per chain. Mixing and reacting 12 them in right stoichiometric proportion would then yield a high molecular weight block copolymer. However, since it is possible to have -CI or -OH mixed end groups on both the homoblocks, the present invention shows that it is possible to do away wjth the stringent requirement stated earlier that each homoblock should have the same identical end groups and the two homoblocks must be mixed in right stoichiometric proportion. Polysulfones usually have some -CI and some -OH end groups. The concentration of each is decided by two important factors: firstly the initial molar ratio of DCDPS to Phenolic monomer and secondly the molecular weight of the polymer, if the mole ratio is not strictly 1:1, that is allowed to build up. The ratio of the two monomers is a very important factor because, in order to build a very high molecular weight, the ratio must be kept closer to 1:1 on a molar basis. Usually, no monomer should be present in a concentration of more than approximately 1-2 mole % higher than the other monomer. Thus, the mole ratio generally remains within the range 1.02:1.00 to 1.00:1.02 to get high molecular weights. An increase in the concentration of any one monomer to a value outside of this range generally results in a disturbance in stoichiometry to such a substantial extent that the molecular weight of the copolymer does not get built up enough and most polymeric properties suffer, as they do not reach optimum values. However, for the preparation for oligomeric homoblocks, such a stringent stoichiometry is not necessary since high molecular weight build up is not required. Thus, for homoblock preparation, a monomer ratio as high as 1.15:1.00 has been employed successfully in the present invention. The monomer ratio range, in homoblock, has 13 thus been increased from 1.02:1.00 to 1.15:1.00, without sacrificing the ultimate molecular weights of the block copolymer. The present invention relates to novel polysulfone block copolymer structures and the novel process by which their preparation takes place. In particular, this invention relates to the preparation of new types of block copolymers made using PSU, PES and PPSU and similar polysulfones and the novel methods of their preparation. The block copolymers may be made using at least two types of different polysulfones and may be made using more than two types of polysulfones. The process of the present invention involves the preparation of novel block copolymers of the poiysulfone family using solution polymerization techniques. These block copolymers are prepared using lower molecular weight, oligomeric homoblocks of, for example, Polyphenylene Sulfone (PPSU) and Poiysulfone (PSU). The invention consists not only of novel block copolymers using the above mentioned homoblocks, but also of the process used for preparation of these novel block copolymers. A major novel and unexpected aspect of the process of the present invention is that it can do away with the stringent requirements that the a given homoblock should have only one type of two end groups as well as the stoichiometry between homoblocks used must be 1:1. Thus, the process of the present invention makes it possible to prepare high molecular weight block copolymers without having identical end groups on each homoblock as well as 14 without the stoichiometry being closely controlled. The present invention therefore greatly simplifies the formation of block copolymers. Also, greater combinations of composition range of block copolymers can be readily made using same homoblocks by this invention as compare to the earlier methods of segmented block copolymer preparations. Of course, using homoblocks with identical end groups and having them in exact stoichiometric proportions does not harm the process in any way, but these are no longer preconditions for the build up of high molecular weight block copolymers. This process also makes it possible by proper control of end groups to prepare block copolymers in which the two homoblocks have a variety of molecular weights and the block copolymer can also have a large range of composition, which was not easy or even not possible in other type of block copolymers discussed earlier. The novel block copolymers are made by first using initially separately prepared lower molecular weight homoblocks with reactive chain end groups. By the term "homoblock", it is meant that each block has either a PSU or PPSU or PES or some such polysulfone structure and dififerent homoblocks have structures differing from each other. The two homoblocks are separately prepared and are arranged to have two end groups which in turn are either the same or different. It is important to realize as taught by this invention that there should be, nevertheless, a near stoichiometric balance of the two differing end groups, in this case say -CI 15 and -OH. What is important is that both end groups are allowed to be present on both the homoblocks. The different ways of preparing homoblocks are as follows: The first set of homoblocks are prepared with predominantly halogen end groups, such as -F, -CI, -Br and -I. The second set of homoblocks are prepared with predominantly the second type of end group, which is capable of reacting with a halogen end group, such as -OH (which may be present as the salts -OK, -ONa, or -OLi). This is done by taking large mole access of dihalo monomer as compared to dihydroxy monomer in the first case and reversing the ratio in the second. In general, when the lower molecular weight homoblock having predominantly one type of end group is reacted with another homoblock having predominantly the second type of end group, block copolymers having high molecular weights are obtained. Thus, for example, reacting low molecular weight PPSU homoblock having predominantly -OH end groups with low molecular weight PSU homoblock having predominantly -CI end groups gives novel block copolymers with [PPSU --PSU]z in the block copolymer sequence. When one homoblock has predominantly all the same end groups (-C1 for example) and is reacted with a second homoblock having predominantly all of a second type of end groups (-OH for example), the block copolymer obtained has blocks of similar molecular weights to the homoblocks. The present invention, this makes it possible for the molecular weights of homoblocks to be nearly same as their molecular weights as block in part of the chains. 16 It is also possible to prepare, according to this invention, block copolymers where the homoblock of PPSU has halogen end groups and the PSU homoblock has phenolic -OH end groups, as well as the reverse where PPSU has the hydroxy end groups and PSU has halogen end groups. As shown by this invention, the end groups may be interchangeable for a given homoblock. Where each homoblocks has non-identical end groups (-C1 and -OH for example), it is important to have them in relatively same stoichiometry counting both the homoblocks. In case of making one or both high molecular weight homoblocks, it is important to keep end groups of both different to the extent possible, as in the case of di-blocks and tri-blocks preparations. It is, however, possible according to this invention to have both homoblocks to have both end groups and still being used for making high molecular weight block copolymers. This can be done by taking both monomers in near equal mole ratio. In such cases, the end groups will be halogen and hydroxy, irrespective of molecular weights. Thus, using the above example, it is possible to make PPSU and PSU homoblocks both having -CI and -OH end groups and reacting together to form block copolymers of desired molecular weight. In such cases, the block copolymers formed may have blocks having in-chain molecular weights, which are similar or higher than the homoblocks" molecular weights. This invention also teaches that besides random homoblock sequence in the block copolymer thus prepared, one can also make di- and tri-block copolymers by 17 adjusting the molecular weights of the homoblocks and the stoichiometry of the two homoblocks reacted to form the block copolymers. The invention therefore teaches preparation of di-block, tri-block as well as segmented block copolymers where the homoblocks may alternate or be present in random sequence. If the molecular weights of the homoblocks are kept low enough and end groups are carefully controlled, this invention makes it possible to build high molecular weight copolymers having essentially alternate homoblock structures in the chains. In such block copolymers all the blocks will have similar molecular weights to those of the two initial homoblocks. If the molecular weights of the homoblocks are kept high, then one can build di- and tri-block copolymers of relatively high molecular weights. It is also another important part of this invention as given above that z, degree of block copolymerization, can be varied from as low as 1 (for a di- block) to as high as 100 or higher for an alternate or random multi block copolymer. It is also another important part of this invention that special tri-block copolymers can also be prepared by using judicious control of the molecular weight, stoichiometry and end groups of the homoblocks. 18 The novel aspect of this invention is the recognition that by varying the stoichiometry of the basic monomers that are used for the preparation of homoblocks, particularly when they are of lower molecular weights, one can make these homoblocks with predominantly known end groups. Thus using one monomer, say, DCDPS in an excess of, say, 3 mole % over Biphenol i.e. a molar stoichiometry of >1.03: 1.00, one obtains PPSU with essentially only -Cl as end groups. This is due to the fact that higher concentrations of DCDPS lead to essentially complete reaction of all of the -OH groups present on Biphenol, thereby limiting the molecular weight build up but providing essentially only -Cl end groups for the homoblock PPSU. Similarly, when Bisphenol A is used at higher concentration in PSU production, one gets essentially all end groups as -. OH, as its Na or K salt. PSU, having essentially these phenolic groups, will not react with itself to give higher molecular weights PSU. Similarly, PPSU with -Cl end groups also cannot react with itself to give higher molecular weight PPSU. Under such conditions, molecular weight does not further increase, giving indication that the chains with other end groups are used up. However, when a homoblock of PPSU with essentially all -Cl end groups is mixed with a homoblock of PSU with essentially all -OK end groups, further polymerization occurs and a PSU-PPSU block is generated. Allowing this reaction to proceed further results in random block copolymer formation with a structure of the type [PSU-PPSU-]z, where z is greater than or equal to 1, and is dependant on the molecular weights of homoblocks, and the stoichiometry and the molecular weight that is allowed to be built up. 19 One important aspect of this invention is deliberate use of higher ratios of the two monomers for the preparation of homoblocks to give essentially one type of end groups. The ratio may be 1.03 - 1.15:1.00, that is having 3 to 15 mole % higher quantity of one monomer over the second monomer. Another important aspect of this invention is that the homoblocks can also be conveniently prepared using near equal stoichiometry of the two base monomers, keeping the molecular weights of the homoblocks as desired and, by mixing, preparing high molecular weight block copolymers of the desired composition. The important aspect of this invention is therefore the preparation of lower molecular weight homoblocks with known end groups and their mixing in the right proportions to yield random block copolymers of higher molecular weights. A further novel and important aspect of this invention is the preparation of di- and tri-block copolymers. These di- and tri-block copolymers are also materials of a novel composition. For this preparation, it is again recognized that homoblocks can be prepared with different molecular weights with essentially known end groups. In general, recognizing that controlling molecular weights of homoblocks and block copolymers give good control on number of homoblocks present in a block copolymer, one can stop the reaction at di or tri block stage. Polysulfones of sufficiently high molecular weight or inherent viscosity, (Inh.V.) are required to give optimum mechanical and other polymer properties, one can 20 bufld that range of molecular weight homoblocks. Thus, PPSU of a number average molecular weight (Mn) say of 50000 with -Cl end groups and PSU of say similar molecular weight with -OK end groups, when mixed and reacted in a proportion of 1:1 on a molar basis will give almost double the molecular weight, giving a di-block. The molecular weight can be controlled on-line using gel permeation chromatography (GPC). If di-blocks are allowed to react further to give still higher molecular weight, we get a tri- and tetra-block and so on. Thus, di-blocks of the structure -[-PSU-PPSU-3- will further react to give tri-blocks of the structure -[-PSU-PPSU-PSU-]- and -[PPSU-PSU-PPSU-]- and which, on further reaction, will yield tetra-blocks and higher multi-blocks. Thus, by controlling molecular weight, stoichiometry and end groups, this invention makes it possible to prepare di-block and tri-block and multi-block copolymers of PSU and PPSU. This invention further makes it possible to prepare a tri block using three different types of homoblocks as follows. First a di block is prepared using two homoblocks, where two end groups present on one homoblock are same and similarly second homoblock has two similar end groups on its chains but different than the first one. This di-block is reacted with third homoblock with two end groups similar to either first or second homoblock to give tri-blocks. 21 The block polymers thus produced may be checked for GPC molecular weight, Inh. V., DSC, Tg, MFI, etc. for quality control. The block copolymers may be used as powder for compounding and subsequently for granulation or may be added as a compatibilizer to the already separately manufactured Mgh molecular weight homologue polysulfones. The present invention seeks to achieve the following: • to provide novel block copolymers of two or more different polysulfone homoblock contents, with controlled structures of di-blocks, tri-blocks and multi-blocks. • to use these homoblocks of polysulfones having low molecular weight and controlled chain end groups to prepare high molecular weight block copolymers. • to prepare high molecular weight di-block and tri-block copolymers using the homoblocks of lower molecular weight and reactive chain ends. • to prepare two types of homoblocks each essentially having either only halogen or hydroxy end groups and thus giving a multi-block copolymer on reaction between the two, the block molecular weight being similar to the initial homoblock molecular weight. s 22 • to prepare block copolymers of two polysulfones, where the ratio of the two homoblocks is in the range 95:5 to 5:95. • to prepare block copolymers of two or more homoblocks of polysulfones, which are transparent and which show a single intermediate Tg. • to prepare block copolymers that are thermally stable and processible in the temperature range of 350°C to 400°C, using traditional injection molding, extrusion or other acceptable plastics processing methods. • to provide a process by which the homoblocks of polysulfones of known molecular weights and controlled end groups are prepared. • to provide a process for the preparation of low molecular weight controlled chain end homoblocks and another process for the preparation of high molecular weight block copolymers having di /tri/multi-block in-chain structures. According to this invention there is provided a process that allows one to prepare low molecular weight, controlled chain-end homoblocks and utilize these homoblocks to prepare di-, tri-, and multi-block copolymers of high molecular weight. 23 The invention preferably uses Sulfolane, NMP, DMAc, DMSO, DMS02, Diphenyl sulfone or any other aprotic organic solvent for the preparation of low molecular weight homoblocks and the high molecular weight block copolymers thereof. Preferably MCB or Toluene or any other non-reacting solvent is used as a diluent and dehydrating agent for the salt formation, dehydration and polymerization steps. Preferably the process uses the above mentioned solvent in the temperature range of 120°C to 250°C and with alkali such as NaOH, KOH, NaHCO3, KHC03; Na2C03 or K2CO3 either by themselves or in a combination of these or any other such suitable alkaline substances. According to this invention there is provided a process of producing novel homoblocks and multi-block copolymers, using an aprotic organic solvent or solvents in the temperature range of 120°C-250°C and then end capping with MeCl or any suitable end capping agent. The process includes the preferred steps of filtration of the salt and precipitation of the block copolymer from the reaction mixture in a non-solvent like H2O or MeOH or a mixture of the two, and then giving further water/or MeOH treatments to reduce the residual solvent content of the powder and subsequently drying the polymeric powder 24 The present invention will now be describe with reference to the following examples. The specific examples illustrating the invention should not be construed to limit the scope thereof. EXAMPLES: EXAMPLE 1: A block copolymer of 50:50 PPSU:PSU (B-0) The following three part procedure was used to prepare this PPSU - PSU block copolymer. Part 1: The preparation of the PPSU homoblock: A 4-necked, 3-litre glass flask was equipped with an overhead stirrer attached to a stainless steel paddle through its center neck. Through one of its side necks, a Cloisonne adapter was attached. The other neck of the Cloisonne adapter was attached to a Dean-Stark trap and a water-cooled condenser. A thermocouple thermometer was inserted through another of the side necks. A nitrogen gas inlet was inserted through the other side neck. The flask was placed in an oil bath, which was connected to a temperature controller. Dimethyl acetamide (DMAc) (873gms, 950ml/mole) and toluene (344gms, 400ml/mole) were placed in the flask and heated to 45°C. Biphenol (186gms) and 4,4"-dichIorodiphenyl sulfone (DCDPS) (307 gms) were added to the flask, the 25 DCDPS and biphenol being in a molar ratio of 1.07:1.00, and the reactants were stirred for 30 minutes. Anhydrous potassium carbonate (152 gms) and sodium carbonate (21 gms) were added to the flask. A nitrogen atmosphere was maintained in the flask by purging. The temperature of the reactants was slowly increased to 165°C over 9 hours and the stirring speed set to 400rpm. The water formed due to the reaction of K2CO3 with biphenol was distilled over as an azeotrope with toluene and collected in the Dean-Stark trap. The toluene was then returned Jo the reaction mixture once it had been separated from the water. Once the water had been completely removed, toluene addition back to reaction vessel was stopped. The toluene was then removed completely from the reaction mixture as the temperature of the reactants increased. The desired temperature was reached after 9 hours. The reaction temperature was then maintained at 165°C and when the viscosity started to increase the stirring speed was raised to 500 rpm Once the viscosity increase slowed, a sample was taken out to check the molecular weight. The GPC Mn achieved was about 32,000, with a Mw of 43,000 and a MWD of 1.34. The reaction mixture was allowed to cool in preparation-for its reaction with the product of part 2. The relatively high molar ratio of DCDPS to Biphenol gave PPSU of a relatively low molecular weight and with predominantly end groups of -Ph-Cl. Part 2: The preparation of the PSU homoblock. DMAc (873gms, 950ml/mole) and toluene (400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. 26 Bisphenol A (244gms) and 4,4"-dichiorodiphenyl sulfone (DCDPS) (287 gms) were added to the flask, the Bisphenol A and DCDPS being in a molar ratio of 1.07:1.00, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (170gms) was added. The toluene acts as an azeotropic solvent. The temperature of the reactants was slowly increased to 165°C over 9 hours and the stirring speed was set to 400 rpm. The water formed due to the, reaction was distilled over as an azeotrope with toluene and collected in the Dean-Stark trap. The toluene was then returned to the reaction mixture once it had been separated from the water. Once the water had been completely removed, toluene addition back to the reaction vessel was stopped. The toluene was then removed completely from the reaction mixture as the temperature of the reactants increased. The desired temperature was reached after 9 hours. The reaction temperature was then maintained at I65°C and when the viscosity started to increase the stirring speed was raised to 500 rpm. At the required Mn of 17,000, MW of about 26,000 and MWD 1.5 the viscosity of the reaction mixture remained almost constant, indicating the end of the polymerization reaction. Part 3: The preparation of the block copolymer. The reaction mixtures of Part 1 and Part 2 were mixed in equal proportions by weight and the block polymerization was conducted at 165°C. After the required MW was achieved, as shown by GPC, the reaction mixture was quenched with DMAc (376gms, 400ml/mole) and its temperature reduced to 160°C. Methyl Chloride gas was then bubbled through the reaction mixture for 5 hrs to ensure 27 complete end capping. The reaction mixture was then diluted with DMAc (600ml/mole) for a second time. The polymer solution was filtered through a 15micron filter in a pressure filter funnel using 2kg/cm2 of nitrogen to remove any salts. The block copolymer was finally recovered by slowly adding the salt-free polymer solution to de-ionized water (13ml/gm of polymer) under high-speed agitation. The precipitated polymer was then recovered by filtration. The precipitated polymer was ground and refluxed three times with de-ionized water at 90°C to completely remove all salts and DMAc. The precipitated polymer was then filtered and dried in an oven at 140°C until the moisture content as determined by Karl Fischer titration was GPC analysis of the block copolymer showed an Mn of 94,000, an Mw of 135,000 and an MWD of 1.44 based on the polystyrene standards. Thus, the copolymer produced had a significantly higher molecular weight than the two homoblocks used as monomer units, indicating the preparation of a block copolymer. The block copolymer powder was then mixed with 0.3% heat stabilizer and 0.2% Ca stearate and granulated using a twin screw extruder. The Tg and the specific gravity of PSU are 189°C and 1.235 respectively, whilst those of PPSU are 222°C and 1.290. The transparent granules of block copolymer showed a DSC Tg of 206°C and a specific gravity of 1.260. The transparency of the granules, the single GPC peak, the intermediate Tg and the specific gravity of the product clearly indicate that a block-copolymer of PSU and PPSU had indeed been formed and that the product was not simply a blend of the two homopolymers, PSU and PPSU. The remaining properties and also those of the blends are given in Table 1. 28 EXAMPLE 2: A block-copolymcr of 75:25 PPSU:PSU (B-l) An experimental set up similar to that described in Example 1 was used. Part 1: The preparation of the PPSU homoblock. DMAc (2679 gms, 950ml/mole) and toluene (1032gms, 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Biphenol (558 gms) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (921 gms) were added to the flask, the DCDPS and biphenol being in a molar ratio of 1.07:1.00, and the reactants were stirred for 30 minutes. Anhydrous potassium carbonate (455gms) and sodium carbonate (64gms) were added to the flask. The toluene acts as an azeotropic solvent. The rest of the procedure is the same as that described in Part 1 of Example 1. The homoblock obtained had a GPC molecular weight of Mn 16,000, an Mw of 25,000 and an MWD of 1.52. Part 2: The preparation of the PSU homoblock. Dimethyl Acetamide (DMAc) (893gms, 950ml/mole) and Toluene (344gms, 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Bisphenol A (244Gms) and 4,4"- 29 dichlorodiphenyl sulfone (DCDPS) (287 gms) were added to the flask, the Bisphenol A and DCDPS being in a molar ratio of 1.07:1.00, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (170 gms) was added to the flask. The toluene acts as an azeotropic solvent. The rest of the procedure is the same as that described in Part 2 of Example 1. The homoblock obtained had a GPC molecular weight of Mn 14,000, an Mw of 21,000 and an MWD of 1.49. Part 3: The preparation of the block copolymer. The reaction mixtures of Part 1 (3 parts) and Part 2 (1 Part) were mixed together and the block polymerization was conducted at 165°C. After the required GPC MW was achieved, the reaction mixture was quenched with DMAc (344gms, 400ml/mole) and its temperature reduced to 160°C. Methyl Chloride gas was then bubbled through the reaction mixture for 5 hrs to ensure complete end capping. The reaction mixture was then diluted with DMAc (600ml/mole) for a second time. The polymer solution was passed through a 15micron filter in a pressure filter funnel using 2kg/cm2 nitrogen to remove any salts. The block copolymer was finally recovered by slowly adding the salt-free polymer solution to de-ionized water (13ml/gm of polymer) under high-speed agitation. The precipitated polymer was then recovered by filtration. The precipitated polymer was treated three times with refluxing de-ionized water at 90°C. The precipitated polymer was then 30 filtered and dried in oven at 140°C until the moisture content as determined by Karl Fisher titration was GPC analysis of the block copolymer showed an Mn of 83,000, an Mw of 119,000 and an MWD of 1.44 based on the polystyrene standards. The block copolymer was then granulated as in Example 1 and its properties were measured. These were a Tg of 210°C and a specific gravity of 1.27. This data, and the product being obtained as clear transparent granules, indicated that PPSU and PSU were present as a block copolymer and not simply as a blend of the two homopolymers. The remaining properties and also those of the blend of similar proportions are given in Table 1. EXAMPLE 3: A Mock copolymer of 25:75 PPSU:PSU (B 2) An experimental set up similar to that described in Example 1 was used. Part 1: The preparation of the PPSU homoblock. DMAc (893 gms, 950ml/mole) and toluene (344gms, 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Biphenol (199gms) and DCDPS (287 gms) were added to the flask, the DCDPS and biphenol being in a molar ratio of 1.00:1.07, and the reactants were stirred for 30 minutes. Anhydrous potassium carbonate (162 gms, 1. l0mole/mole) and sodium carbonate (23gms) were then added to the flask. 31 DMAc (2679 gms, 950ml/mole) and toluene (1032gms 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Bisphenol A (226ms) and DCDPS (921 gms) were added to the flask, the Bisphenol A and DCDPS being in a molar ratio of 1.00:1.07, and the > reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (486 gms) was then added to the flask. The rest of the procedure is same as that described in Part 2 of Example 1. The homoblock obtained had a GPC molecular weight of Mn 14,000, an Mw of 21,000 and an MWD of 1.49 based on the polystyrene standards. Part 3: The preparation of the block copolymer. The reaction mixtures of Part 1(1 part) and Part 2 (3 parts) were mixed together and the block polymerization was conducted at 165°C. After the required GPC MW was achieved, the reaction mixture was quenched and the copolymer worked up as in Example 1. 32 GPC analysis of the copolymer showed an Mn of 79,000, an Mw of 114,000 and an MWD of 1.44. The block copolymer powder was then extruded and granulated as per the procedure given in Example 1. The DSC Tg of the copolymer was 195°C and the specific gravity was 1.24. This data, and the product being obtained as light amber colored transparent granules, indicated that the polymer obtained was indeed a block copolymer and not simply a blend of PPSU and PSU. The remaining properties and also those of the blends are given in Table 1. EXAMPLE 4: A copolymer of 90:10 PPSU:PSU (B 3) An experimental set up similar to that described in Example 1 was used. Part 1: The preparation of the PPSU homoblock. DMAc (3215 gms, 950ml/mole) and toluene (1238gms, 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Biphenol (670 gms) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (1075 gms), were added to the flask, the DCDPS and biphenol being in a molar ratio of 1.04:1.00, and the reactants were stirred for 30 minutes. Anhydrous potassium carbonate (546gms) and sodium carbonate (76gms) were added to the flask. The toluene acts as an azeotropic solvent. 33 The rest of the procedure is the same as that described in Part I of Example 1. The homoblock obtained had a GPC molecular weight of Mn 22,000, an Mw of 26,000 and an MWD of 1.16. Part 2: The preparation of the PSU homoblock. DMAc (357 gms, 950ml/mole) and Toluene (138gms 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Bisphenol A (96gms) and DCDPS (115 gms) were added to the flask, the Bisphenol A and DCDPS being in a molar ratio of 1,05:1.00, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (64 gms) was added to the flask. The toluene acts as an azeotropic solvent. The reaction vessel was evacuated using a vacuum pump and filled with nitrogen. The rest of the procedure is the same as that described in Part 2 of Example 1. The homoblock obtained had a GPC molecular weight of Mn 18,000, an Mw of 29,000 and an MWD of 1.62 Part 3: The preparation of.the block copolymer. The reaction mixtures of Part 1 (9 parts) and Part 2(1 Part) were mixed together and the block polymerization conducted at 165°C. After the required GPC MW was achieved, the reaction mixture was quenched with DMAc (376gms, 400ml/mole) and its temperature reduced to 160°C. Methyl Chloride gas was then 34 bubbled through the reaction mixture for 5 hrs to ensure complete end capping. The reaction mixture was then diluted with DMAc (564gms, 600ml/mole) for a second time. The polymer solution was passed through a 15micron filter in a pressure filter funnel using 2kg/em2 nitrogen to remove any salts. The block copolymer was finally recovered by slowly adding the salt-free polymer solution to de-ionized water (I3ml/gm of polymer) under high-speed agitation. The precipitated polymer was recovered by filtration. The precipitated polymer was treated three times with refluxing de-ionized water at 90°C. The precipitated polymer was then filtered and dried in an oven at 140°C until the moisture content as determined by Karl Fisher titration was GPC analysis of the copolymer showed an Mn of 80,000, an Mw of 110,000 and an MWD of 1.36 based on polystyrene standards. The block copolymer was then granulated as in Example 1 and its properties were measured. These were a Tg of 215°C and a specific gravity of 1.28. This data, and the product being obtained as clear transparent granules, indicated that PPSU and PSU were indeed present as a block copolymer and not just as a blend of the two homopolymers. The remaining properties and also those of the blends are given in Table 1. 35 EXAMPLE 5: Physical Blends of PPSU and PSU: In order to study the properties of the physical blending of PPSU and PSU dry blending of the powders was carried out in the following proportions, followed by extrusion on ZE25 twin screw extruder and evaluation (Table 1). C1 : PPSU powder (50%) + PSU powder (50%) C2 : PPSU powder (75%) + PSU Powder (25%) C3 : PPSU powder (25%) + PSU powder (75%) The PPSU used was the commercially available GAFONE -P 4300 grade and the PSU used was the commercially available GAFONE -S PSU 1300, both from Gharda Chemicals Ltd. India. EXAMPLE 6: Copolymer of 90:10 of PPSU-PSU (B 4) An experimental set up similar to that described in Example I was used. Part 1: The preparation of the PPSU homoblock. DMAc (8037 gms, 950ml/mole> and toluene (3096gms, 4GGml/moIe) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Biphenol (1674 gms) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (2635 gms), were added to the flask, the DCDPS and biphenol being in a molar 36 ratio of 1.02:1.00, and the reactants were stirred for 30 minutes. Anhydrous potassium carbonate (1366gms) and anhydrous sodium carbonate (191gms) were added to the flask. The toluene acts as an azeotropic solvent. The rest of the procedure is the same as that described in Part 1 of Example 1. The bamablack obtained bad a GPC molecular weight of Mn 17,000, an Mw of 26,000 and an MWD of 1.54. Part 2: The preparation of the PSU homoblock. DMAc (893 gms, 950ml/mole) and toluene (344gms 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Bisphenol A (239gms) and 4,4"-dichIorodiphenyl sulfone (DCDPS) (287 gms) were added to the flask, the Bisphenol A and DCDPS being in a molar ratio of 1.05:1.00, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (167 gms) was added to the flask. The toluene acts as an azeotropic solvent. The rest of the procedure is the same as that described in Part 2 of Example 1. The homoblock obtained had a GPC molecular weight of Mn 10,000, an Mw of 15,000 and an MWD of 1.50 Part 3: The preparation of the block copolymer. 37 The reaction mixtures of Part 1 (9 parts) and Part 2(I Part) were mixed together and the block polymerization was conducted at 165°C. After the required GPC MW was achieved, the reaction mixture was quenched with DMAc (376gms, 400ml/mole) and its temperature reduced to 160°C. Methyl Chloride gas was then bubbled through the reaction mixture for 5 hrs to ensure complete end capping. The reaction mixture was then diluted with DMAc (564gms, 600ml/mole) for the second time. The polymer solution was passed through a 15micron filter in a pressure filter funnel using 2kg/cm2 nitrogen to remove any salts. The block copolymer was finally recovered by slowly adding the salt-free polymer solution to de-ionized water (13ml/gm of polymer) under high-speed agitation. The precipitated polymer was recovered by filtration. The precipitated polymer was treated three times with refluxing de-ionized water at 90°C. The precipitated polymer was then filtered and dried in an oven at 140°C, until the moisture content as determined by Karl Fisher titration was GPC analysis of the block copolymer showed an Mn of 80,000, an Mw of 115,000 and an MWD of 1.44 based on polystyrene standards. The block copolymer was then granulated as in Example 1 and its properties were measured. These were a Tg of 2I6°C and a specific gravity of 1.28. This data, and the product being obtained as clear transparent granules, indicated that PPSU and PSU were indeed present as a block copolymer and not simply as a blend of the two homopolymers. The remaining properties and also those of the blends are given in Table 2. 38 EXAMPLE 7: A block copolymer of 90:10 PPSU:PSU (B 5) An experimental set up similar to that described in Example 1 was used. Part 1: The preparation of the PPSU homoblock. DMAc (8037 gms, 950ml/mole) and toluene (3096gms, 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Biphenol (1674 gms) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (2816 gms) were added to the flask, the DCDPS and biphenol being in a molar ratio of 1.09:1.00, and the reactants were stirred for 30 minutes. Anhydrous potassium carbonate (1366gms) and anhydrous sodium carbonate (191gms) were added to the flask. The toluene acts as an azeotropic solvent. The rest of the procedure is the same as that described in Part 1 of Example 1. The homoblock obtained had GPC molecular weights of Mn 42,000, an Mw of 55,000 and an MWD of 1.31. Part 2: Preparation of the PSU Homoblock. DMAc (893 gms, 950ml/mole) and toluene (344gms 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Bisphenol A (244gms) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (287 gms), were added to the flask, the Bisphenol A and DCDPS being 39 in a molar ratio of 1.07:1.00, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (170 gms) was added to the flask. The toluene acts as an azeotropic solvent. The rest of the procedure is the same as that described in Part 2 of Example 1. The homoblock obtained had GPC molecular weights of Mn 18,000, an Mw of 24,000 and an MWD of 1.34. Part 3: The preparation of the block copolymer. The reaction mixtures of Part 1 (9 parts) and Part 2(1 Part) were mixed together and the block polymerization was conducted at 165°C. An insufficient viscosity rise took place during the polymerization. The GPC analysis showed an Mn of 48,000, an Mw of 67,000 and an MWD of 1.39, so an extra 0.04mole/mole of biphenol was added and the polymerization was continued. After the required GPC MW was achieved, the reaction mixture was quenched with DMAc (376gms, 400ml/mole) and its temperature reduced to 160°C. Methyl Chloride gas was then bubbled through the reaction mixture for 5 hrs to ensure complete end capping. The reaction mixture was then diluted with DMAc (564gms, 600ml/mole) for a second time. The polymer solution was passed through a 15micron filter in a pressure filter funnel using 2kg/cm2 nitrogen to remove any salts. The block copolymer was finally recovered by slowly adding the salt-free polymer solution to de-ionized water (13ml/gm of polymer) under high-speed agitation. The precipitated polymer was then recovered by filtration. The precipitated polymer 40 was treated three times with refluxing de-ionized water at 90°C. The precipitated polymer was then filtered and dried m an oven at 140°C until the moisture content as determined by Karl Fisher titration was GPC analysis of the copolymer showed an Mn of 93,000, an Mw of 132,000 and an MWD of 1.41 based on polystyrene standards. The block copolymer was then granulated as in Example 1 and its properties were measured. These were a Tg of 219°C and a specific gravity of 1.28. This data, and the product being obtained as clear transparent granules, indicated that PPSU and PSU were indeed present as a block copolymer and not simply as a blend of the two homopolymers. The remaining properties and also those of the blends are given in Table 2. EXAMPLE 8: A block copolymer of 80:20 PPSU:PSU (B 6) An experimental set up similar to that described in Example 1 was used. Part 1: The preparation of the PPSU homoblock. DMAc (7144 gms, 950ml/mole) and toluene (2752gms, 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Biphenol( 1488 gms ) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (2503 gms) were added to the flask, the DCDPS and biphenol being in a molar ratio of 1.09:1.00, and the reactants were stirred for 30 minutes. Anhydrous 41 potassium carbonate (1215gms) and anhydrous sodium carbonate (170gms) were added to the flask. The toluene acts as an azeotropic solvent. The rest of the procedure is the same as that described in Part 1 of Example 1. The homoblock obtained had GPC molecular weights of Mn 42,000, an Mw of 53,000 and an MWD of 1.25. Part 2: The preparation of the PSU homoblock. DMAc (1786 gms, 950ml/mole) and toluene (688gms 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Bisphenol A (524gms) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (574gms), were added to the flask, the Bisphenol A and DCDPS being in a molar ratio of 1.15:1.00, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (365 gms) was added to the flask. The toluene acts as an azeotropic solvent. The rest of the procedure is the same as that described in Part 2 of Example 1. The homoblock obtained had GPC molecular weights of Mn 17,000, an Mw of 23,000 and an MWD of 1.33 Part 3: The preparation of the block copolymer. 42 The reaction mixtures of Part 1 (8 parts) and Part 2 (2 Part) were mixed together and the polymerization was conducted at 165°C. When the GPC molecular weight showed an Mw of 94,000. The reaction mass was quenched with DMAc (376gms, 400ml/mole) and its temperature reduced to 160°C. Methyl Chloride gas was then bubbled through the reaction mixture for 5 hrs to ensure complete end capping. The reaction mixture was then diluted with DMAc (564gms, 600ml/mole) for a second time. The polymer solution was passed through a 15micron filter in a pressure filter funnel using 2kg/cm nitrogen to remove any salts. The block copolymer was finally recovered by slowly adding the salt-free polymer solution to de-ionized water (13ml/gm of polymer) under high-speed agitation. The precipitated polymer was then recovered by filtration. The precipitated polymer was treated three times with refluxing de-ionized water at 90°C. The precipitated polymer was then filtered and dried in an oven at 140°C until the moisture content as determined by Karl Fisher titration was GPC analysis of the copolymer showed an Mn of 68,000, an Mw of 96,000 and an MWD of 1.40 based on Polystyrene standards. The block copolymer was then granulated as in Example 1 and its properties were measured. These were a Tg of 210°C and a specific gravity of 1.27. This data, and the product being obtained as clear transparent granules, indicated that PPSU and PSU were indeed present as a block copolymer and not simply as a blend of the two homopolymers. The remaining properties and also those of the blends are given in Table 2. 43 EXAMPLE 9: The solubility of a block copolymer of 90:10 PPSU:PSU Polyphenylene sulfone (PPSU) is insoluble in tetrahydrofuran (THF) at 65°C, whereas polyether sulfone (PSU) is soluble. The 90:10 PPSU:PSU block copolymer was only 0.64% soluble in THF, clearly indicating its block structure. The other block copolymers of PPSU-PSU (B-0, B-1 and B-2) were also soluble in THF. EXAMPLE 10 : The hydrolytic stability of a block copolymer Samples of the PPSU-PSU block copolymer from Example No. 6 were kept in boiling water at 100°C for 7 days. The tensile properties of the samples were measured before and after their boiling in water and the results are shown below: Tensile properties before boiling in water after boiling in water Tensile Strength(Mpa) 73 70 Tensile Modulus(Mpa) 1915 1900 Elongation at break(%) 69 70 This data indicates that there is no drop in the tensile strength of the block copolymer after being stored in boiling water for 7 days and hence it can find applications where hydrolytic stability is important. 44 Table 1 PROPERTIES COMPARISION OF PPSU-PSU COPOLYMERS WITH NEAT PPSU & NEAT PSU & THEIR BLENDS: PROPERTY PPSU PSU C-1 PPSU=75 % PSU =25 % C-2 PPSU=50 % PSU =50% C-3 PPSU=25 % PSU = 75 % B-0 PPSU=50% PSU=50% B-1 PPSU=75% PSU=25% B-2 PPSU=25% PSU=75% B-3 PPSU=90% PSU-10% Mn 80 90 85 94 97 94 83 79 80 Mw 111 129 122 131 135 135 119 114 110 MWD 1.39 1.44 1.43 1.39 1.39 1.44 1.40 1.44 1.36 SPECIFIC GRAVITY 1.290 1.235 1.277 1.259 1.248 1.26 1.27 1.248 1.28 TENSILE STRENGTHCMpa ) 74 76 75 78 76 74 75 76 76 TENSILE MODULUS(Mpa ) 2500 2300 2195 2400 2304 2175 2252 2501 2281 ELONGATION @BRECK% >80 >80 68 ? 60 36 48 44 59 IMPACT STRENGTH(J/M ) 650 45 117 76 61 97 94 61 160 FLEXURAL STRENGTH (Mpa) 100 114 104 108 105 110 111 113 99 45 2518 2293 2478 2402 2228 2200 2455 2323 2439 FLEXURAL MODULUS 7.4 8.4 7.3 8.0 (Mpa) YIELD STRESS 194 215 206 210 (%) 191&221 189 Tgl&Tg2(°C) 223 192&221 183 188 166 198 192 191&220 HDT (° C) 38 23 12.8 28 13 MVRat 400°C/2.16kg/6* The higher impact properties, one intermediate Tg and transparency of granules indicate that BQ, Bl, B2 & B3 are block copolymers, and not just physical mixtures like CI, C2 & C3. 46 EXAMPLE 11: A block-coporj mer of 75:25 PSU:PES (BC-07) The following three part procedure was used to prepare this PSU - PES block copolymer. Part 1: The preparation of the PSU homoblock. DMAc (873gms, 950ml/mole) and toluene (4G0ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Bisphenol A (684gms) and 4,4"~dichlorodiphenyl sulfone (DCDPS) (886.8 gms) were added to the flask, the DCDPS and Bis Phenol A being in a molar ratio of 1.03:1.00, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (476gms) was added. The toluene acts as an azeotropic solvent. The temperature of the reactants was slowly increased to 165°C over 9 hours and the stirring speed was set to 400 rpm. The water formed due to the reaction was distilled over as an azeotrope with toluene and collected in the Dean-Stark trap. The toluene was then returned to the reaction mixture once it had been separated from the water. Once the water had been completely removed, toluene addition back to the reaction vessel was stopped. The toluene was then removed completely from the reaction mixture as the temperature of the reactants increased. The desired temperature was reached after 9 hours. The reaction temperature was then maintained at 165°C and when the viscosity started to increase the stirring speed was raised to 500 rpm. At the required Mn of 13,000, MW of about 17,000 47 and MWD 1.36 the viscosity of the reaction mixture remained almost constant, indicating the end of the polymerization reaction. Part 2: The preparation of the PES homoblock: A 4-necked, 3-litre glass flask was equipped with an overhead stirrer attached to a stainless steel paddle through its center neck. Through one of its side necks, a Cloisonne adapter was attached. The other neck of the Ooisonne adapter was attached to a Dean-Stark trap and a water-cooled condenser. A thermocouple thermometer was inserted through another of the side necks. A nitrogen gas inlet was inserted through the other side neck. The flask was placed in an oil bath,-which was connected to a temperature controller. Dimethyl acetamide (DMAc) (873gms, 950ml/mole) and toluene (344gms, 400ml/mole) were placed in the flask and heated to 45°C. DHDPS (257.5gms) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (287 gms) were added to the flask, the DHDPS and DCDPS being in a molar ratio of 1.03:1.00, and the reactants were stirred for 30 minutes. Anhydrous potassium carbonate (158.7 gms) added to the flask. A nitrogen atmosphere was maintained in the flask by purging. The temperature of the reactants was slowly increased to 165°C over 9 hours and the stirring speed set to 400rpm. The water formed due to the reaction of K2CO3 with DHDPS was distilled over as an azeotrope with toluene and collected in the Dean-Stark trap. The toluene was then returned to the reaction mixture once it had been separated from the water. Once the water had been completely removed, toluene addition back to reaction vessel was stopped. The toluene was then removed 48 completely from the reaction mixture as the temperature of the reactants increased. The desired temperature was reached after 9 hours. The reaction temperature was then maintained at 165°C and when the viscosity started to increase the stirring speed was raised to 500 rpm. Once the viscosity increase slowed, a sample was taken out to check the molecular weight. The GPC Mn achieved was about 22,000, with a Mw of 25,000 and a MWD of 1.15. The reaction mixture was allowed to cool in preparation for its reaction with the product of part 2. The relatively high molar ratio of DCDES to DHDPS gave PPSU of a relatively low molecular weight and with predominantly end groups of-Ph-Cl. Part 3: The preparation of the block copolymer. The reaction mixtures of Part l(3part) and Part 2 (1 part) were mixed by weight proportion and the block polymerization was conducted at 165°C. After the required MW was achieved, as shown by GPC, the reaction mixture was quenched with DMAc (376gms, 400ml/mole) and its temperature reduced to 140°C. Methyl Chloride gas was then bubbled through the reaction mixture for 5 hrs to ensure complete end capping. The reaction mixture was then diluted with DMAc (600ml/mole) for a second time. The polymer solution was filtered through a 15micron filter in a pressure filter funnel using 2kg/cm2 of nitrogen to remove any salts. The block copolymer was finally recovered by slowly adding the salt-free polymer solution to de-ionized water (13ml/gm of polymer) under high-speed agitation. The precipitated polymer was then recovered by filtration. The precipitated polymer was ground and refluxed three times with de-ionized water at 49 90°C to completely remove all salts and DMAc. The precipitated polymer was then filtered and dried in an oven at 140°C until the moisture content as determined by Karl Fischer titration was GPC analysis of the block copolymer showed an Mn of 77,000, an Mw of 108,000 and an MWD of 1.39 based on the polystyrene standards. Thus, the copolymer produced had a significantly higher molecular weight than the two homoblocks used as monomer units, indicating the preparation of a block copolymer. The block copolymer powder was then mixed with 0.3% heat stabilizer and granulated using a twin screw extruder. The Tg and the specific gravity of PSU are 190°C and 1.24 respectively, whilst those of PES are 224°C and 1 37. The transparent granules of block copolymer showed a DSC Tg of 198°C and a specific gravity of 1.27. The transparency of the granules, the single GPC peak, the intermediate Tg and the specific gravity of the product clearly indicate that fl block-copolymer of PSU and PES had indeed been formed and that the product was not simply a blend of the two homopolymers, PSU and PES. The remaining properties and also those of the blends are given in Table 1. EXAMPLE 12: A block-copolymer of 50:50 PSU:PES (B-8) An experimental set up similar to that described in Example 1 was used. Part 1: The preparation of the PSU homoblock. 50 Dimethyl Acetamide (DMAc) (1786 gms, 950ml/mole) and Toluene (688 gms, 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Bisphenol A (461Gms) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (574 gms) were added to the flask, the Bisphenol A and DCDPS being in a molar ratio of 1.01:1.00, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate(318 gms) was added to the flask. The toluene acts as an azeotropic solvent. The rest of the procedure is the same as that described in Part 1 of Example 1. The homobiock obtained had a GPC, molecular weight of Mn 8,000, an Mw of 11,000 and an MWD of 1.43. Part 2: The preparation of the PES homobiock. DMAc (1786 gms, 950ml/mole) and toluene (688 gms, 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. DHDPS (500 gms) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (586 gms) were added to the flask, the DCDPS and DHDPS being in a molar ratio of 1.02:1.00, and the reactants were stirred for 30 minutes. Anhydrous potassium carbonate (318 gms) was added to the flask. The toluene acts as an azeotropic solvent. The rest of the procedure is the same as that described in Part 2 of Example 1. The homobiock obtained had a GPC molecular weight of Mn 28,000, an Mw of 34,000 and an MWD of 1.21. 51 Part 3: The preparation of the block copolymer. The reaction mixtures of Part 1 and Part 2 were mixed together and the block polymerization was conducted at 165°C. After the required GPC MW was achieved, the reaction mixture was quenched with DMAc (344gms, 400ml/mole) and its temperature reduced to 140°C. Methyl Chloride gas was then bubbled through the reaction mixture for 5 hrs to ensure complete end capping. The reaction mixture was then diluted with DMAc (600ml/mole) for a second time. The polymer solution was passed through a 15micron filter in a pressure filter funnel using 2kg/cm2 nitrogen to remove any salts. The block copolymer was finally recovered by slowly adding the salt-free polymer solution to de-ionized water (13ml/gm of polymer) under high-speed agitation. The precipitated polymer was then recovered by filtration. The precipitated polymer was treated three times with refluxing de-ionized water at 90°C. The precipitated polymer was then filtered and dried in oven at 140°C until the moisture content as determined by Karl Fisher titration was GPC analysis of the block copolymer showed an Mn of 67,000, an Mw of 92,000 and an MWD of 1.37 based on the polystyrene standards. The block copolymer was then granulated as in Example 1 and its properties were measured. These were a Tg of 208°C and a specific gravity of 1.3. This data, and the product being obtained as clear transparent granules, indicated that PES and PSU were present as a block copolymer and not simply as a blend of the two homopolymers. 52 The remaining properties and also those of the blend of similar proportions are given in Table 1. EXAMPLE 13: A block copolymer of 25:75 PSUrPES (BC 09) An experimental set up similar to that described in Example 1 was used. Part 1: The preparation of the PSU homoblock. DMAc (893 gms, 950ml/mole) and toluene (344 gms 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Bisphenol A (232 gms) and DCDPS (287 gms) were added to the flask, the Bisphenol A and DCDPS being in a molar ratio of 1.00:1.02, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (162 gms) was then added to the flask. i The rest of the procedure is same as that described in Part 1 of Example 1. The homoblock obtained had a GPC molecular weight of Mn 17,000, an Mw of 22,000 and an MWD of 1.29 based on the polystyrene standards. Part 2: The preparation of the PES homoblock. DMAc (2679 gms, 950ml/mole) and toluene (1032gms, 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and 53 heated to 45°C. DHDPS (750 gms) and DCDPS (878 gms) were added to the flask, the DCDPS and DHDPS being in a molar ratio of 1.02:1.00, and the reactants were stirred for 30 minutes. Anhydrous potassium carbonate (476 gms, 1.15mole/mole) added to the flask. The rest of the procedure is same as that described in Part 2 of Example 1, The homobiock obtained had a GPC molecular weight of Mn 15,000, an Mw of 20,000 and an MWD of 1.33 based on the polystyrene standards. Part 3: The preparation of the block copolymer. The reaction mixtures of Part 1 (1 part) and Part 2 (3 parts) were mixed together and the block polymerization was conducted at 165°C. After the required GPC MW was achieved, the reaction mixture was quenched and the copolymer worked up as in Example 1. GPC analysis of the copolymer showed an Mn of 68,000, an Mw of 104,000 and an MWD of 1.53. The block copolymer powder was then extruded and granulated as per the procedure given in Example I. The DSC Tg of the copolymer was 218°C and the specific gravity was 1.33. This data, and the product being obtained as light amber colored transparent granules, indicated that the polymer obtained was indeed a block copolymer and not simply a blend of PSU and PES. The remaining properties and also those of the blends are given in Table 3. 54 EXAMPLE 14: A block copolymer of 10:90 PSU:PES (BC 10) An experimental set up similar to that described in Example 1 was used. Part 1: The preparation of the PSU homoblock. DMAc (357 gms, 950ml/mole) and toluene (138 gms 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. Bisphenol A (93 gms) and DCDPS (115 gms) were added to the flask, the Bisphenol A and DCDPS being in a molar ratio of 1.02:1.00, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (65 gms) was then added to the flask. The rest of the procedure is same as that described in Part 1 of Example 1. The homoblock obtained had a GPC molecular weight of Mn 49,000, an Mw of 63,000 and an MWD of 1.29 based on the polystyrene standards. Part 2: The preparation of the PES homoblock. DMAc (3215 gms, 950ml/mole) and toluene (1238gms, 400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 45°C. DHDPS (900 gms) and DCDPS (1044 gms) were added to the flask, the DCDPS and DHDPS being in a molar ratio of 1.01:1.00, and the 55 reactants were stirred for 30 minutes. Anhydrous potassium carbonate (571 gms, 1.15mole/mole) added to the flask. The rest of the procedure is same as that described in Part 2 of Example 1. The homoblock obtained had a GPC molecular weight of Mn 35,000, an Mw of 51,000 and an MWD of 1.46 based on the polystyrene standards. Part 3: The preparation of the block copolymer. The reaction mixtures of Part 1 (1 part) and Part 2 (9 parts) were mixed together and the block polymerization was conducted at 165°C. After the required GPC MW was achieved, the reaction mixture was quenched and the copolymer worked up as in Example 1. GPC analysis of the copolymer showed an Mn of 87,000, an Mw of 113,000 and an MWD of 1.29. The block copolymer powder was then extruded and granulated as per the procedure given in Example 1. The DSC Tg of the copolymer was 222°C and the specific gravity was 1.357. This data, and the product being obtained as light amber colored transparent granules, indicated that the polymer obtained was indeed a block copolymer and not simply a blend of PSU and PES. The remaining properties and also those of the blends are given in Table 3. 56 EXAMPLE 15: Physical Blends of PSU and PES: In order to study the properties of the physical blending of PPSU and PSU dry blending of the powders was carried out in the following proportions, followed by extrusion on ZE 25 twin screw extruder and evaluation (Table 3). C1 : PSU powder (75%) + PES powder (25%) C2: PSU powder (50%) + PES Powder (50%) C3 : PSU powder (25%) + PES powder (75%) C4 : PSU powder (10%) + PES powder (90%) The PES used was the commercially available GAFONE - 3300 grade and the PSU used was the commercially available GAFONE -S PSU 1300, both from Gharda Chemicals Ltd. India. 57 Table 3 PROPERTIES COMPARISION OF PPSU-PSU COPOLYMERS WITH NEAT PSU & NEAT PES & THEIR BLENDS; PROPERTY PES PSU C-l PSU=75 % PES =25 % C-2 PSU=50 % PES =50 % C-3 PSU=25 % PES =75 % C-4 PSU=90% PES =10% BC-7 PSU=75% PES=25% BC-8 PSU=50% PES~50% BC-9 PSU=25% PES=75% BC-10 PSU=10% PES=90% Mn 86 90 In all cases Extrusion was not FAILED due to immiscibility of PES & PSU. 77 67 68 87 Mw 120 129 108 92 104 113 MWD 1.39 1.44 1.39 1.37 1.53 1.29 SPECIFIC GRAVITY 1.37 1.235 1.27 1.3 1.33 1.357 TENSILE STRENGTH(Mpa) 76 82 72 88 TENSILE MODULUS(Mpa) 2300 1993 2457 2110 ELONGATION BRECK % 80 53 25 17 IMPACT STRENGTH(J/M) 45 4.8 4.9 5.1 5.2 FLEXURAL STRENGTH (Mpa) 114 112 124 119 FLEXURAL MODULUS (Mpa) 2455 2776 2931 2843 YIELD STRESS (%) 7 ""7.5 7.3 7.7 Tgl&Tg2(°C) 189 198 208 218 223 HDT (° C) 166 58 MVR at 380°C/2.16kg/6" 40.25 28 60.9 The g and transparency of granules indicate that BC7, BC8, BC9 & BC10 are block copolymers and not just physical mixtures like C1, C2, C3 & C4. are not miscible. 59 EXAMPLE 16: A block-copolymer of 90:10 PES : PPSU (D-2) The following three part procedure was used to prepare this PES - PPSU block copolymer. Part 1: The preparation of the PES homoblock. DMAc (2876gms, 850ml/mole) and toluene (400ml/mole) were placed in the flask, through which nitrogen gas was bubbled continuously, and heated to 65°C. 4,4"-dihydroxydiphenyl sulfone (DHDPS) (900 gms) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (1044 gms) were added to the flask, the DCDPS and DHDPS being in a molar ratio of 1.01:1.00, and the reaction mixture was stirred for 30 minutes. Anhydrous potassium carbonate (572gms) was added. The toluene acts as an azeotropic solvent. The temperature of the reactants was slowly increased to 165°C over 9 hours and the stirring speed was set to 400 rpm. The water formed due to the reaction was distilled over as an azeotrope with toluene and collected in the Dean-Stark trap. The toluene was then returned to the reaction mixture once it had been separated from the water. Once the water had been completely removed, toluene addition back to the reaction vessel was stopped. The toluene was then removed completely from the reaction mixture as the temperature of the reactants increased. The desired temperature was reached after 9 hours. The reaction temperature was then maintained at 165°C and when the viscosity started to increase the stirring speed was raised to 500 rpm. At the 60 required Mn of 11,000, MW of about 14,000 and MWD 1.20 the viscosity of the reaction mixture remained almost constant, indicating the end of the polymerization reaction. Part 2: The preparation of the PPSU homoblock: A 4-necked, 3 -litre glass flask was equipped with an overhead stirrer attached to a stainless steel paddle through its center neck. Through one of its side necks, a Cloisonne adapter was attached. The other neck of the Qoisonne adapter was attached to a Dean-Stark trap and a water-cooled condenser. A thermocouple thermometer was inserted through another of the side necks. A nitrogen gas inlet was inserted through the other side neck. The flask was placed in an oil bath, which was connected to a temperature controller. Dimethyl acetamide (DMAc) (357gms, 950ml/mole) and toluene ( 400ml/mole) were placed in the flask and heated to 45°C. Biphenol (75.9) and 4,4"-dichlorodiphenyl sulfone (DCDPS) (114.8 gms) were added to the flask, the Biphenol and DCDPS being in a molar ratio of 1.02:1.00, and the reactants were stirred for 30 minutes. Anhydrous potassium carbonate (61 gms) Anhydrous Sodium carbonate (8.5 gms) ware added to the flask. A nitrogen atmosphere was maintained in the flask by purging. The temperature of the reactants was slowly increased to 165°C over 9 hours and the stirring speed set to 400rpm. The water formed due to the reaction of K2CO3& Na2C03 with Biphenol was distilled over as an azeotrope with toluene and collected in the Dean-Stark trap. The toluene was 61 then returned to the reaction mixture once it had been separated from the water. Once the water had been completely removed, toluene addition back to reaction vessel was stopped. The toluene was then removed completely from the reaction mixture as the temperature of the reactants increased The desired temperature was reached after 9 hours. The reaction temperature was then maintained at 165°C and when the viscosity started to increase the stirring speed was raised to 500 rpm. Once the viscosity increase slowed, a sample was taken out to check the molecular weight. The GPC Mn achieved was about 17,000, with a Mw of 22,000 and a MWD of 1.33, The reaction mixture was allowed to cool in preparation for its reaction with the product of part 2. The relatively high molar ratio of DCDPS to Biphenol gave PPSU of a relatively low molecular weight and with predominantly end groups of-Ph-Cl. Part 3: The preparation of the block copolymer. The reaction mixtures of Part 1(9 part) and Part 2 (1 part) were mixed by weight proportion and the block polymerization was conducted at 165°C. After the required MW was achieved, as shown by GPC, the reaction mixture was quenched with DMAc (376gms, 400ml/mole) and its temperature reduced to 140°C. Methyl Chloride gas was then bubbled through the reaction mixture for 5 hrs to ensure complete end capping. The reaction mixture was then diluted with DMAc (600ml/mole) for a second time. The polymer solution was filtered through a 15micron filter in a pressure filter funnel using 2kg/cm2 of nitrogen to remove any salts. The block copolymer was finally recovered by slowly adding the salt-free 62 polymer solution to de-ionized water (13ml/gm of polymer) under high-speed agitation. The precipitated polymer was then recovered by filtration. The precipitated polymer was ground and refluxed three times with de-ionized water at 90°C to completely remove all salts and DMAc. The precipitated polymer was then filtered and dried in an oven at 140°C until the moisture content as determined by Karl Fischer titration was GPC analysis of the block copolymer showed an Mn of 78,000, an Mw of 112,000 and an MWD of 1.43 based on the polystyrene standards. Thus, the copolymer produced had a significantly higher molecular weight than the two homoblocks used as monomer units, indicating the preparation of a block copolymer. The block copolymer powder was then mixed with 0.3% heat stabilizer and granulated using a twin screw extruder. The Tg and the specific gravity of PES are 224°C and 1.37 respectively, whilst those of PPSU are 223°C and 1.29. The transparent granules of block copolymer showed a DSC Tg of224°C and a specific gravity of 1.36. The transparency of the granules, the single GPC peak, the intermediate Tg and the specific gravity of the product clearly indicate that a block-coporymer of PES and PPSU had indeed been formed and that the product was not simply a blend of the two homopolymers, PES and PPSU. Various homoblocks can be prepared using one or more dichloro compounds and one or more dihydroxy compounds, some of which are listed below: 63 AROMATIC DIHALO COMPOUNDS: Dichloro diphenyl sulfone (DCDPS), 4,4" Bis (4 - chlorophenyl sulfonyl) biphenyl (CSB), Dichloro Benzophenone, Dichloro diphenyl ether, Dichloro biphenyl, Dichloro diphenyl methylene, Di Methyl dichloro diphenyl sulfone, tetra methyl dichloro diphenyl sulfone. AROMATIC DIHYDROXY COMPOUNDS: Dihydroxy diphenyl Sulfone (DHDPS), Bisphenol A, Biphenol, Hydroquinone, Dimethyl Dihydroxy diphenyl sulfone, Tetramethyl dihydroxy diphenyl sulfone, Tetramethyl Bisphenol A, Tetramethyl Biphenol. 64 We claim: 1) A process of preparing a block copolymer comprising of at least two types of homoblocks, all belonging to the polysulfone family, wherein each of the said homoblock has an identical or different molecular weight of at least 1000 and has at least 5% of the overall weight and wherein the block copolymer has a molecular weight of at least 2000, the process steps comprising of: (a) preparing each of the aforesaid homoblocks by heating at least one aromatic diol with at least one aromatic dihalo compound, one of which contains at least one sulfone group, in the presence of at least one alkali optionally in at least one solvent and further optionally in the presence of an azeotropic agent, (b) reacting the aforesaid homoblocks together at a temperature between 130°C to 250°C optionally in at least a solvent, and further optionally followed by end-capping said block copolymer, (c) recovering the block copolymer. 2) A process as claimed in claim 1 wherein the block copolymer is recovered by washing the reaction mass to remove the salt and alkali and optionally the solvent. 65 3) A process as claimed in claim 1 wherein the block copolymer prepared in at least one solvent is recovered from the solvent by filtering out the salt and precipitating the block copolymer in water or MeOH or a mixture of water and MeOH and further filtering, washing and drying block copolymer. 4) A process as claimed in claim 1 wherein the block copolymer prepared in at least one solvent is recovered by filtering the salt and distilling off the solvent. 5) A process as claimed in claim 1, wherein the aromatic dihalo compound is dihalodiphenyl sulphone or dihalodiphenyl ketone or dihalodiphenyl ether or dihalodiphenyl methylene or dihalodiphenyl biphenyl. 6) A process as claimed in claim 5, wherein the said dihalodiphenyl sulfone is Dichlorodiphenyl sulfone (DCDPS) or 4,4" Bis (4-Chloro Diphenyl disulfonyl) biphenyl (CSB). 7) A process as claimed in claim 5, wherein the said dihalodiphenyl ketone is Dichlorodiphenyl ketone. 8) A process as claimed in claim 5, wherein the said dihalodiphenyl ether is Dichlorodiphenyl ether. 9) A process as claimed in claim 5, wherein the said dihalodiphenyl methylene is Dichlorodiphenyl methylene. 66 10) A process as claimed in claim 5, wherein the said dihalodiphenyl biphenyl is Dichlorodiphenyl biphenyl. 11) A process as claimed in claim 1, wherein the aromatic diol is Bisphenol A or Biphenol or Bisphenol S or their dimethyl or tetramethyl derivatives. 12) A process as claimed in claim 1, wherein either of the aromatic diol or the aromatic dihalo compound is equal in moles or greater than the other up to 15 mole %. 13) A process as claimed in claim 1, wherein each of the aforesaid homoblock has at least 10% of the overall weight of the block copolymer. 14) A process as claimed in claim 1, wherein each of the aforesaid homoblock has at least 25% of the overall weight of the block copolymer. 15) A process as claimed in claim 1, wherein each of the aforesaid homoblock has at least 40% of the overall weight of the block copolymer. 16) A process as claimed in claim 1, wherein the solvent is Dimethyl acetamide (DMAc), Dimethyl Sulphoxide (DMSO), Sulfolane, N-Methyl Pyrrolydone, diphenyl sulfone, dimethyl sulfone or a mixture thereof. 67 17) A process as claimed in claim 1, wherein the alkali is a metal hydroxide, or a mixture of two or more metal hydroxides. 18) A process as claimed in claim 17, wherein the metal hydroxide is NaOH, KOH or a mixture thereof. 19) A process as claimed in claim 1, wherein the alkali is a metal carbonate or a mixture of two or more metal carbonates. 20) A process as claimed in claim 19, wherein the metal carbonate is Na2CO3, K2CO3, or a mixture thereof. 21) A process as claimed in claim 1, wherein the alkali is a mixture of a metal hydroxide and a metal carbonate. 22) A process as claimed in claim 1, wherein the process steps (a) or (b) or both are carried out at a temperature between 160°C to 230°C. 23) A process as claimed in claim 1, wherein the said azeotropic agent is toluene. 24) A process as claimed in claim 1, wherein the said azeotropic agent is monochlorobenzene. 68

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