Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF AROMATIC POLYESTERS

Abstract

An improved process for the preparation of aromatic polyesters which comprises polymerizing an aromatic dicarboxylic acid substituted with a polar group having weight percentage in the range of 20 to 75, with an alkali metal salt of tetra substituted aromatic diol having weight percentage in the range of 25 to 78 in presence of solubilizing additive such as herein described having weight percentage in the range of 2 to 20 at a temperature in the of-5 to 80°C for a period in the range of 1 to 36 hr with stirring, adding the reaction mixture to a nonsolvent such as herein described, separating and purifying the precipitated polymer by conventional methods, drying the polymer at a temperature in the range of 40 to 80° C for a time in the range of 24 to 48 to obtain pure polymer.

Full Text

The present invention relates to an improved process for the preparation of aromatic polyesters (polynrylntre). These are prepared from tetra- substituted aromatic diol or bisphenol and a polar group substituted aromatic dicarboxylic acid. These polar groups could be a halogen, nitro, sulfo or similar polar group or combination of these groups. The polymerization process uses an alkali metal salt of tetra alkyl substituted aromatic diol or bisphenol in combination with an additive instead of plain bisphenol in the method of solution polymerization. Polyesters are high performance engineering plastics with good combination of thermal, mechanical and gas permeation properties. Aromatic polyesters synthesized with polar group substituted acids and tetra alkyl substituted bisphenol simultaneously have high gas permeability as well as selectivity and thus are useful as membrane materials for gas separation applications. These polymers when dissolved in a suitable solvent can be used to form hollow fiber membranes or flat sheet membranes by phase inversion processes or thin film composite membranes by dip coating methods. Membranes made of these polyesters have generally superior permeation properties for gas separations such as hydrogen from methane, helium from nitrogen, or oxygen from nitrogen etc. In the prior art, aromatic polyesters (polyarylates) are prepared either by one phase (solution or melt) or two phase (interfacial) polycondensation methods [G. Allen et al, eds. Comprehensive Polymer Science, Ist edn, Pergaman press, Oxford, (1989); P.W. Morgan, Condensation Polymers by interfacial and solution methods, Interscience, NY (1965)]. P.K. Bhowmik et al (Macromolecules 26, 5287 - 5294, 1993) have synthesized polyarylates based on bromoterephthalic acid and biphenyls or binaphthyls in 90-95% yields and moderate intrinsic viscosities by melt condensation method. J. Lin et al (Macromolecules 25, 7107 - 7113, 1992) have prepared polyarylates based on bromoterephthalic acid and nitro terephthalic acid with hydroquinone sulfonate by interfacial polymerization method with 34 - 53 % yields having intrinsic viscosity of 0.27 to 0.48. Polyarylates based on bisphenol-A, hexafluorobisphenol-A, 9,9-bis(4-hydroxy phenyl) fluorene and 3-(4-hydroxyphenyl)-1,1,3-trimethyl-5-indanol have been synthesized with tetrafluoro isophthalic acid (M. Kakimoto et al, J. Polym. Sci.: Part A: Polym. Chem., 25, 2747 - 2753, 1987) and with tetrafluoro terephthalic acid (Y. Oishi et al, J. Polym. Sci.: Part A: Polym. Chem., 27, 1425 - 1428, 1989) by interfacial and solution polymerization in good yields. No literature was found on the preparation of aromatic polyesters based on tetra- substituted bisphenols and the polar group substituted aromatic dicarboxylic acid. Also, the process of solution polymerization normally uses a combination of bisphenol and an organic base. The present method of solution polymerization using an alkali metal salt of the bisphenol along with a suitable additive in order to obtain aromatic polyesters having high intrinsic viscosity and yield is not reported in the literature. The object of present invention is to provide an improved process for the preparation of aromatic polyesters based on tetra- substituted bisphenol and polar group substituted aromatic dicarboxylic acid having high viscosity and yield. Accordingly, the present invention provides an improved process for the preparation of aromatic polyesters which comprises polymerizing an aromatic dicarboxylic acid substituted with a polar group having weight percentage in the range of 20 to 75, with an alkali metal salt of tetra- substituted aromatic diol having weight percentage in the range of 25 to 78 in presence of solubilizing additive such as herein described having weight percentage in the range of 2 to 20 at a temperature in the range of -5 to 80°C for a period in the range of 1 to 36 hr with stirring, adding the reaction mixture to a nonsolvent such as herein described, separating and purifying the precipitated polymer by conventional methods, drying the polymer at a temperature in the range of 40 to 80°C for a time in the range of 24 to 48 hours to obtain pure polymer. Method of preparation of aromatic polyesters consist of dissolving the tetra-substituted bisphenol in aqueous alkali metal hydroxide, preferably sodium or potassium hydroxide, evaporating water initially by distillation and finally under vacuum and then polymerizing this salt with a polar group substituted aromatic dicarboxylic acid chloride in the presence of a suitable additive by solution polymerization method as: suspending the sodium or potassium salt of tetra alkyl substituted bisphenol in an organic solvent, adding appropriate proportions of the additive, allowing it to react with a polar group substituted aromatic dicarboxylic acid chloride dissolved in organic solvent at ambient temperature and pressure for 1 to 24 hours with stirring, adding the reaction mixture to a nonsolvent, separating the precipitated polymer by conventional methods like filtration to obtain the crude polymer, further purifying this crude polymer by dissolving it in a suitable organic solvent, adding this solution to a nonsolvent, separating the precipitated polymer by conventional methods like filtration, drying the polymer at 40 to 80°C under normal or reduced pressure, for 24 to 48 hours to obtain pure polymer. In an embodiment,, the tetra- substituted bisphenol used may have the structural formula as shown in Figure la, where R1, R2 = alkyl group containing C1 to C10, (Formula Removed) phenyl, or , or combination of these groups and R3, R4 = alkyl group containing C1 to C5, phenyl, F, Cl, Br, or I or combination of these groups or Figure 1b, where R = alkyl group containing C1 to C5, phenyl, F, Cl, Br, or I or combination of these groups; i.e. the bisphenol used may be such as tetramethylbisphenol-A, tetramethylhexafluorobisphenol-A, 4,4'-(9-fluorenylidene)bis(2,6-dimethylphenol), tetramethylphenolphthalein, tetrabromobisphenol-A, tetrabromohexafluorobisphenol-A, 4,4'- (9-fluorenylidene)bis(2,6-dibromophenol), tetrabromophenolph-thalein, dibromodimemylbisphenol-A, dibromodimethylhexafluorobisphenol-A, 4,4'-(9- fluorenylidene)bis(2-bromo-6-methylphenol), dibromodimethylphenolphthalein and any other tetra- substituted dihydric phenols or tetra- substituted bisphenols. In an another embodiment of the present invention, the polar group substituted aromatic dicarboxylic acid used may be having the structural formula as shown in Figure 2, wherein, R1, R2, R3, R4 = F, Cl, Br, I or any other polar group or combination of these groups or R1, R2, R3, = F, Cl, Br, I or any other polar group or combination of these groups and R4 = H, or R1, R2 = F, Cl, Br, I or any other polar group or combination of these groups and R3, R4 = H, or RI, - F, Cl, Br, I, NO2, S03H or S03Na or any other polar group and R2, R3, R4 = H, i.e. the aromatic dicarboxylic acid(s) used may have the structural formula as shown in Figure 2, wherein one / two / three / all four H atoms of the phenyl ring are replaced by a polar group such as halogen atom (F, Cl, Br or I), NO2, SO3H or SO3Na. i.e. the acid used may be such as to monobromoisophthalic acid, monobromoterephthalic acid, monochloro-isophthalic acid, monochloroterephthalic acid, monofluoroisophthalic acid, monofluoro-terephthalic acid, nitroterephthalic acid, dibromoisophthalic acid, dibromoterephthalic acid, dichloroisophthalic acid, dichloroterephthalic acid, difluoroisophthalic acid, difluoro-terephthalic acid, tetrabromoisophthalic acid, tetrabromoterephthalic acid, tetrachloro-isophthalic acid, tetrachloroterephthalic acid, tetrafluoroisophthalic acid, tetrafluoro-terephthalic acid, or other polar group or halogen atom substituted aromatic dicarboxylic acid. In another embodiment, the additive used may be such as crown ether or quaternary ammonium salt like tetrabutyl ammonium bromide or benzyltriethyl ammonium chloride. In another embodiment, the solvent used for polymerization may be such as chloroform, methylene chloride, dioxane, tetrahydrofuran, nitrobenzene, dimethylformamide and dimethylacetamide and similar organic solvents. In another embodiment, the nonsolvent used may be such as water, acetone, methyl ethyl ketone, methanol, ethanol, or other simple alcohols or ketones or mixture of these solvents. as In yet another embodiment, the solvent for making polymer solution may be such chloroform, methylene chloride, tetrachloromethane, dioxane, tetrahydrofuran, nitrobenzene, toluene, dimethylformamide, dimethylacetamide and similar organic solvents. The process of the present invention is described with the following examples which are illustrative only, and should not be construed to limit the scope of the present invention in any manner. Example 1 Stirring 20 ml of methylene chloride, 1.64 g (5 x 10-3 mol) of disodium tetramethylbisphenolate and 0.114g (5 x 10-4 mol) of benzyltriethyl ammonium chloride in a 50 ml capacity flask equipped with nitrogen gas inlet; separately dissolving 1.3 g of nitroterephthaloyl dichloride (5.25 x 10-3 mol) in 7 ml of methylene chloride and then adding formed solution dropwise to above reaction mixture with stirring over a period of 15 minutes, continuing the stirring for overnight and then pouring the reaction mixture into an excess of methanol, followed by filtering the precipitated polymer and washing it with water, drying it in oven at 50°C, again purifying this polymer by dissolving it in chloroform, filtering the solution and reprecipitating in methanol followed by collecting the polymer under suction and drying it in vacuum at 50°C to obtain 1.95 g (88 % yield) of pure polymer which had intrinsic viscosity of 0.76 dL/g in sym-tetrachloroethane at 35°C and gas permeation properties as given in Table 1. Example 2. Dissolving 20 ml of methylene chloride, 1.64 g (5 x 10-3 mol) of disodium tetramethylbisphenolate and 0.114g (5 x 10"4 mol) of benzyltriethyl ammonium chloride in a 50 ml capacity flask equipped with nitrogen gas inlet; separately dissolving 1.48 g of bromoterephthaloyl dichloride (5.25 x 10-3 mol) in 7 ml of methylene chloride and then adding this acid chloride solution in a dropwise manner to the above reaction mixture with stirring over a period of 15 minutes, continuing the stirring for overnight and then pouring the reaction mixture into an excess of methanol, followed by filtering the precipitated polymer and washing it with water, drying it in oven at 50°C, again purifying this polymer by dissolving it in chloroform, filtering the solution and reprecipitating in methanol followed by collecting the polymer under suction and drying it in vacuum at 50°C to obtain 2.1 g (83 % yield) of pure polymer which had intrinsic viscosity of 0.47 dL/g in sym-tetrachloroethane at 35°C and gas permeation properties as given in Table 2. The main advantages of this work are: i. The polymers based on tetra alkyl substituted bisphenol and polar group substituted aromatic dicarboxylic acid obtained by this method have high intrinsic viscosity coupled with high yield. On the contrary, the polymer obtained by conventional solution polycondensation method have low intrinsic viscosity and moderate yields while the same polymer obtained by an interfacial polycondensation method have low viscosity as well as low yields. ii. The polyarylates prepared from polar group substituted aromatic dicarboxylic acids such as nitroterephthalic or bromoterephthalic acid have in general high gas permeability and excellent selectivity compared to polyarylates made from the same bisphenol and conventional acids such as isophthalic or terephthalic acid; and can thus be used for gas separation such as hydrogen from methane, helium from nitrogen, oxygen from nitrogen etc. The intrinsic permeation properties of some of these polymers can be compared with that for polymers obtained from respective diol and unsubstituted acid as given in following Tables 1 and 2. Table 1. Permeability (p) and selectivity (a) for various gas pairs for polyarylates based on tetramethylbisphenol-A with nitroterephthalic acid (TMbisA-NT) as well as with terephthalic acid (TMbisA-T). (Table Removed) Table 2. Permeability (P) and selectivity (a) for various gas pairs for polyarylates based on tetramethylbisphenol-A with bromoterephthalic acid (TMbisA-BrT) as well as with terephthalic acid (TMbisA-T). (Table Removed) iii. The aromatic polyester made from tetramethylbisphenol-A with nitroterephthalic acid or bromoterephthalic acid has excellent permeability and very good selectivity for He, H2 as well as for O2. iv. One of the advantage of the present work is that these aromatic polyesters are easily processed into membrane form of hollow fiber, flat sheet or thin film composite type membranes as these aromatic polyesters are easily soluble at ambient temperature in common solvents such as such as chloroform, methylene chloride, dioxane, tetrahydrofuran, toluene, dimethylformamide and dimethylacetamide. v. In particular, these aromatic polyesters have an excellent separation factor for various gas pairs coupled with adequately high intrinsic helium, hydrogen and oxygen permeabilities. We Claim: 1. An improved process for the preparation of aromatic polyesters which comprises polymerizing an aromatic dicarboxylic acid substituted with a polar group having weight percentage in the range of 20 to 75, with an alkali metal salt of tetra-substituted aromatic diol having weight percentage in the range of 25 to 78 in presence of solubilizing additive such as herein described having weight percentage in the range of 2 to 20 at a temperature in the range of -5 to 80°C for a period in the range of 1 to 36 hr with stirring, adding the reaction mixture to a nonsoivent such as herein described, separating and purifying the precipitated polymer by conventional methods, drying the polymer at a temperature in the range of 40 to 80°C for a time in the range of 24 to 48 hours to obtain pure polymer. 2. An improved process as claimed in claim 1 where the tetra-substituted aromatic diol used having structural formula as shown in Figure 1a.of drauing accompanying where R1, R2 = alkyl group containing C1 to (Formula Remvoed) -b. Cl, Br, or I or combination of these groups. C1o, CF3, phenyl, or , or combination of these groups and R3, R4 = alkyl group containing c1 to C5, phenyl, F, Cl, Br, or I or combination of these groups of, as shown in Figure 1b. of drauing accompanying where R = alkyl group containing C1 to C5, phenyl, F, 3. An improved process as claimed in claims 1-2 wherein the aromatic diol used is tetramethylbisphenol-A, tetramethylhexafluorobisphenol-A, 4,4'-(9-fluorenylidene) bis(2,6-dimethylphenol), tetramethylphenolphthalein, tetrabromobisphenol-A, tetrabromohexafluorobisphenol-A, 4,4'-(9-fluorenylidene)bis(2,6-dibromophenol), tetrabromophenolph-thalein, dibromodimethylbisphenol-A, dibromodimethylhexafluorobisphenol-A, 4,4'-(9-fluorenylidene)bis(2-bromo-6- methylphenol), dibromodimethylphenolphthalein and any other tetra- substituted dihydric phenols or tetra- substituted bisphenols. 4. An improved process as claimed in claims 1 and 3 wherein the polar group substituted aromatic dicarboxylic acid used is having the structural formula as shown in Figure 2,of the drauing accompanying the specification wherein, R1, R2, R3, R4 = F, Cl, Br, I or any other polar group or combination of these groups or R1,R2, R3, = F, Cl, Br, I or any other polar group or combination of these groups and R4 = H or R1, R2 = F, Cl, Br, I or any other polar group or combination of these groups and R3, R4 = H orR1, = F, Cl, Br, I, NO2, SO3H or SO3Na or any other polar group and R2, R3, R4 = H 5. An improved process as claimed in claims 1-4 wherein the aromatic dicarboxylic acid used may be having the structural formula as shown in Figure 2, wherein one / two / three / all four H atoms of the phenyl ring are replaced by a polar group such as halogen atom (F, Cl, Br or I), NO2, SO3H or SO3Na. i.e. the acid used may be such as to monobromoisophthalic acid, monobromoterephthalic acid, monochloro-isophthalic acid, monochloroterephthalic acid, monofluoroisophthalic acid, monofluoro-terephthalic acid, nitroterephthalic acid, dibromoisophthalic acid, dibromoterephthalic acid, dichloroisophthalic acid, dichloroterephthalic acid, difluoroisophthalic acid, difluoro-terephthalic acid, tetrabromoisophthalic acid, tetrabromoterephthalic acid, tetrachloro-isophthalic acid, tetrachloroterephthalic acid, tetrafluoroisophthalic acid, tetrafluoro-terephthalic acid, or other polar group or halogen atom substituted aromatic dicarboxylic acid. 6. An improved process as claimed in claims 1 to 5 wherein the solubilize additive used is such as crown ether or quaternary ammonium salt selected from tetrabutyl ammonium bromide or benzyltriethyl ammonium chloride. 7. An improved process as claimed in claims 1 to 6 wherein the solvent used for polymerization is chloroform, methylene chloride, dioxane, tetrahydrofuran, nitrobenzene, dimethylformamide and dimethylacetamide and similar organic solvents. 8. An improved process as claimed in claims 1 to 7 wherein the nonsolvent used is cuoh -as water, acetone, methyl ethyl ketone, methanol, ethanol, or other simple alcohols and ketones or combination of these solvents. 9. An improved process as claimed in claims 1 to Swherein the solvent used for making polymer solutip^Kused is suen as cMoroform, methvje'ne chloride, tetrachloromethape; dioxane, /fetrahydrjafuran, nitrobenzene, toluene, dimethylfoj^namide, dimethylacetamide. 9 An improved process as claimed in claims 1 to 9, wherein the polymerization reaction is carried out at 0 to 80°C. 10. An improved process as claimed in claims 1 to 10 wherein the polymerization reaction is carried out at the stirring rate of 0 to 5000 rpm. 11 An improved process for the preparation of aromatic polyesters as herein described with reference to the examples and the drawings accompanying this specification.

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112-del-1998-abstract.pdf

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112-del-1998-correspondence-others.pdf

112-del-1998-correspondence-po.pdf

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112-del-1998-form-2.pdf

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112-del-1998-petition-138.pdf