Title of Invention

A PROCESS FOR THE PREPARATION OF POLYMERIC MIXTURES BASED ON EP (D) M ELASTOMER COPOLYMERS

Abstract

process with two or more steps for the preparation in suspension of mixtures of ethylene- propylene (EPM) elastomer homopolymers or ethylene- propylene-diene (EPDM) elastomer terpolymers in the presence of a catalytiC system essentiallY consist- ing of a compound of vanadium and a cocatalyst es- 10 sentiallY consisting of an Aluminium alkyl and in the presence of an activator, the above process being characterized in that: in the first step a first polymerization of the monomers is carried out in the presence of the Vanadium based catalyst; in the second or subsequent steps further polymerizable monomers and activator are added to the Suspension of the polymer obtained in step (a).

Full Text

PROCESS FOR THE PREPARATION OF POLYMERIC MIXTURES BASED ON EP(D)M ELASTOMER COPOLYMERS Abstract Process with two or more steps for the prepara-5 tion in suspension of mixtures of ethylene-propylene (EPM) elastomer homopolymers or ethylene-propylene-diene (EPDM) elastomer terpolymers in the presence of a catalytic system essentially consist¬ing of a compound of Vanadium and a cocatalyst es-10 sentially consisting of an Aluminium alkyl and in the presence of an activator, the above process be¬ing characterised in that: a) in the first step a first polymerisation of the monomers is carried out in the presence of the Va- 15 nadium based catalyst; b) in the second or subsequent steps further polym- erizable monomers and activator are added to the suspension of the polymer obtained in step (a). PROCESS FOR THE PREPARATION OF POLYMERIC MIXTURES BASED ON EP(D)M ELASTOMER COPOLYMERS The present invention relates to a process for the preparation of elastomer mixtures of copolymers and terpolymers of ethylene and propylene. More specifically, the present invention re¬lates to a process for obtaining bimodal ethylene/propylene and ethylene/propylene/diene elastomers directly in the polymerisation reaction. Bistep (or multistep) processes are known in literature for the synthesis of bimodal products; in the case of polyethylene these processes exploit the high lifetime of the catalysts to have the pos¬sibility of obtaining polymers with different mo¬lecular weights in the various steps (see for example EP-A-057420 and EP-A-649860). The above system is effective in the field of plastic materials but cannot be applied to proc¬esses in suspension for the production of elastomer (CO) and {ter)polymers, as the typical catalysts for this process could not guarantee the elas-tomeric properties typical of EP(D)M. Other patents exist in which products with a wide molecular weight distribution or bimodal prod¬ucts are obtained in a single reactor with the use of catalysts based on various transition metals (US-A-5.401.816; US-A-5.399.540; EP-A-480.376) or containing different salts of the same metal {EP-A-314.i65). This type of process does not enable the compo¬sitions of the polymers generated by the various catalytic sites to be independently controlled. For this reason, the above patents also mainly relate to plastic materials, in which the predominant presence of a component makes the composition dis¬tribution have little influence on the characteris-:ics of the product. It is also known that, with respect to the process for the production of ethylene-propylene elastomers in suspension, a process which is pref¬erable for its low cost, high productivity and re-iuced environmental impact, the catalytic system :raditionally used is based on Vanadium salts. At lormal operating temperatures, this catalytic sys-cem has a high deactivation rate which does not al-low a bistep-type process to be economically and technically satisfactory. In addition the slurry of the elastomer polymer in an irregular form creates typical problems of fouling-stickiness so that the transfer phases of the polymeric slurry from one reactor to another can be very critical. It is also known that blends subsequently ob-tained in the processing phase, as well as causing increases in operating costs, do not have such com¬pletely homogenised polymeric phases, as in the case of a blend obtained in polymerisation. In EP-A-717,050 and EP-A-751,155 filed by the same applicant, supported and/or prepolymerized catalysts based on Vanadium are described, capable of producing ethylene-propylene elastomers {co and ter polymers) in a subdivided form with a con¬trolled morphology in heterogeneous processes, preferably of the suspension type, thus reducing fouling of the polymerisation reactor, A process has now been found which enables the production of the above elastomer polymeric mix¬tures directly in the polymerisation environment without the disadvantages described above. In accordance with this, the present invention relates to a process with two or more steps for the preparation in suspension of mixtures of ethylene-propylene (EPM) elastomer homopolymers or ethylene-propylene-diene (EPDM) elastomer terpoiymers in the presence of a catalytic system essentially consist¬ing of a compound of Vanadium, as such or supported on an inert carrier, and a cocatalyst essentially consisting of an Aluminium alkyl having the general formula R„A1X„ wherein R is a C,-C2o alkyl radi¬cal, X is a halogen, m+n = 3, m is an integer from 5 0 to 2, and in the presence of an activator, the above process being characterised in that: a} in the first step a first polymerisation of the monomers is carried out in the presence of the catalyst based on Vanadium, the cocatalyst and op¬tionally in the presence of the activator, the mo¬lar ratio cocatalyst/Vanadium being from 5 to 500, preferably from 7 to 50; up to a conversion degree of at least 1000 grams of polymer per gram of Vana¬dium thus obtaining a suspension of the polymer in a liquid phase; b) in the second or subsequent steps further polym-erizable monomers are added to the suspension of polymer obtained in step (a) together with further activator in order to have a molar ratio between activator, sum of the optional activator of step (a) and the activator of step (b), and Vanadium of from 4 to 50; and with further cocatalyst so as to have a ratio between the cocatalyst of step (b) and Vanadium of step (a) of from 5 to 500, preferably from 7 to 50; the polymerisation reaction being Continued up to a conversion of at least 3000 grams of polymer per gram of catalyst. In the preferred embodiment, the activator is used already in step (a) in a quantity of from 1 to 10, preferably from 2 to 5, moles of activator per mole of Vanadium. Again in step (a) the molar ratio cocatalyst/Vanadium is from 5 to 500, preferably from 7 to 50. The catalysts based on Vanadium which can be Used in the process of the present invention are selected from: supported and/or prepolymerised catalysts based on Vanadium described in EP-A-717,050 and Ep-A-751,155; Vanadyl trihalides, alkoxyhalides and alkoxides; Vanadium and Vanadyl acetylacetonates and chloro acetylacetonates. In the preferred embodiment the catalyst be¬longs to the group of supported and/or prepolymer¬ised catalysts based on Vanadium described in the above Italian patent applications and Vanadium and Vanadyl acetylacetonates. As far as the activatots are concerned, these are generally halogenated organic compounds of the type chloro alkanes or chloro esters such as for example CHCI3, CCl,, ethyltrichloroacetate or n-butylperchlorocrotonate. In the preferred embodi¬ment the activator is ethyltrichloroacetate. The reaction medium in which the elastomer polymer, once formed, is suspended consists of the same polymerisable monomers present in liquid phase. It is preferable however to use inert dilu¬ents, such as saturated hydrocarbons, preferably propane. The polymerisation temperature is usually be¬tween 15°C and 65°C, preferably from 25°C to 50°C, and the total pressure can vary from 8 to 80 bars, preferably from 12 to 40 bars. The polymerisation reaction, both in step (a) and in step (b), can be optionally carried out in the presence of a molecular weight regulator, such as diethylzinc and hydrogen, preferably hydrogen. If hydrogen is used as molecular weight regula¬tor, the partial hydrogen pressure in the reaction system, step (a) + step {b), is usually from 0.2 to 20 bars, preferably from 0.5 to 10 bars. In a pre¬ferred embodiment step (a) is carried out without hydrogen, which is used instead in step (b). As far as the reaction time of step (a) is concerned, this is usually between 10 and 18 0 min¬utes, preferably from 20 to 80 minutes; step (b) on the other hand is normally from 10 to 360 minutes, preferably from 20 to 80 minutes: With respect to the molar ratio between ethyl¬ene and propylene in liquid phase, this can vary from 0.08 to 1, preferably from 0.11 to 0.8. If EPDM terpolymers are desired, the third monomer is a non-conjugated diene selected from: dienes with a linear chain such as 1,4-hexadiene and 1,6-octadiene; branched dienes such as 5-methyl-l,4-hexadiene; 3,7-dimethyl-1,6-octadiene; 3,7-dimethyl-1,7-octadiene; dienes with a single ring such as 1,4-cyclohexadiene; 1,5-cyclooctadiene; 1,5-cyclododecadiene; dienes having bridge-linked rings such as meth- yltetrahydro indene; dicyc iopentadiene; bicyclo[2.2.l]hepta2,5-2,5-diene; alkenyl, alkylid- ene, cycloalkenyl and cycloalkylidene norbornenes such as 5-methylene-2-norbornene; 5-ethylidene-2-norbornene (ENB); 5-propenyl-2-norbornene. Among non-conjugated dienes typically used for preparing these copolymers, dienes containing at least one double bond in a strained ring are pre¬ferred, even more preferably 5-ethylidene-2-norbornene (ENB). If the third monomer is used, the concentration of the latter in liquid phase can vary from 0.1 to 0.5% molar. At the end of the process of the present inven¬tion, the polymer thus obtained can be separated with the usual techniques well known to experts in the field, for example in the form of pressed balls or in granular form, after evaporation (or strip¬ping) of the solvent and any possible non-reacted monomers and subsequent drying. In a preferred embodiment however, at the end of step (b) the polymer is recovered according to the process described in Italian patent appli¬cations IT-A-MI 95 1910 and IT-A-MI 95 2499. With the process of the present invention, it is possible to directly obtain in reaction bimodal polymers resulting from the mixing of polymers with different molecular weights obtained in the various polymerisation steps. The EP(D)M polymers which can be obtained with the process of the present invention are products with a controlled morphology, having excellent elastomeric characteristics and excellent homogene¬ity between the phases inside the polymeric particles. The process of the present invention also en¬ables the composition and molecular weight of each single component to be controlled to obtain the de¬sired characteristics. The process as described herein refers to reac¬tions carried out in batch, but the process can ob¬viously be carried out in continuous, which is more advantageous from an economical point of view. It is also evident that, depending on the char¬acteristics desired, the process of the present in¬vention can be carried out in 2 or more steps. The following examples provide a better illus¬tration of the present Invention. EXAMPLES The following examples refer to tests carried out in a laboratory with 3 litre reactors which op¬erate batchwise. All the reagents are commercial products, the solvents and liquid activators were de-aerated un¬der nitrogen and anhydrified on alumina or molecu¬lar sieves- The copolymers obtained were characterised as follows: Composition and reactivity ratio These were determined by infra-red analysis of the polymer in the form of film with a thickness of 0.2 mm. using an FTIR spectrophotometer of Perkin Elmer model 1760. The propylene content was determined by measur¬ing the ratio between the band absorbances at 4390 and 4255 cm"^ and using a calibration curve obtained with standard polymers. Mooney Viscosity ML(l+4): this was deter¬mined at 100 °C and 125°C according to the method ASTM D1646-87. -- Molecular weight distribution (M^/M^^) . This was determined with gel permeation chroma¬tography, in 1,2-dichlorobenzene at 135 °C, using 4 columns in series containing, as stationary phase, PL-GEL^ (product of Polymer Lab) with particles of 10 m having a porosity of 10^, 10^, 10\ 10^ nm, re¬spectively. The calculation of the molecular weights was corrected in relation to the average composition of the polymer according to the equa¬tion proposed by Sholte. The melting heat correlated to the crystallinity of the polymers was determined by DSC with a Perkin-Elmer DSC7 instrument in an inert at¬mosphere and with a scanning rate of 20°C/min. The crystallinity datum was obtained by relating the melting heat of the polymer to the melting heat of the polyethylene estimated at 286 J/g. The viscoelastlc tests were carried out with a DMTA MKII mechanical dynamic analyzer of Polymer Lab, in shear mode at 130 °C in frequency scanning. The intrinsic viscosity was determined in 1/2-di-chlorobenzene at 135°C. The catalyst used in experimental examples 1, 2 and 3 is a catalyst prepared according to the method indicated in example 10 of EP-A-75i,155. Comparative EXAMPLE 1 (copolymerisation of Ethylene and propylene). 1675 ml of liquid propylene are charged into a perfectly anhydrous 2.8 dm2 pressure-resistant re¬actor equipped with a propeller stirrer. The reac¬tor is thermostat-regulated at 40°C, saturated with ethylene until an overpressure of 6.0 bars is reached, and a further overpressure of 0.2 bars of hydrogen is then added. The total pressure in the top of the reactor was 21.7 bars. A hexane solution containing 1,76 ininoles of DEAC (Diethylaluminum chloride) is then added and subsequently an aliquot of the catalyst containing 0.039 mmoles of Vanadium suspended in hexane and 0.157 mraoles of ethyltrichloroacetate (ETCA, molar ratio Al/V = 40, molar ratio ETCA/V =4). The reaction is carried out for 60 minutes at a constant temperature feeding ethylene in continuous to keep the total pressure constant. At the end of this period the reactor was opened and 130 g of polymer in the form of agglomerated particles were recovered. The characterisations of this polymer are shown in table 1. EXAMPLE 2 (copolymerisation of ethylene and propylene). 1864 ml of liquid propylene are charged into the same reactor as example 1. The reactor is thermostat-regulated at 4 0 °C and saturated with ethylene until an overpressure of 5.55 bars is reached. The total pressure in the top of the reac¬tor was 21.05 bars. A hexane solution containing 1.56 mmoles of DEAC is then added and subsequently an aliquot of the catalyst containing 0.039 mmoles of Vanadium suspended in hexane and 0.118 mmoles of ETCA (molar ratio Al/V = 40, molar ratio ETCA/V = 3). The reaction is carried out at a constant tem¬perature feeding ethylene in continuous to keep the total pressure constant. After 60 minutes the reaction was practically exhausted. The mixture was left under stirring for a few minutes, 3 bars of hydrogen were then added and the mixture was then saturated with a further 5 bars of ethylene (total ethylene pressure = 10.55 bars). A hexane solution containing 1.56 mmoles of DEAC and 0.118 mmoles of ETCA was then added to the reactor (total molar ratio Al/V = 80, total molar ratio ETCA/V = 6). The polymerisation restarted (ethylene consump¬tion and exothermicity), and was carried out feed¬ing ethylene to maintain the total pressure constant. After 60 minutes from the beginning of the second polymerisation the monomers were evapo-cated and the reactor was opened. 128 grams of polymer in agglomerated particles were recovered. The characterisations relating to this polymer are shown in table 1. EXAMPLE 3 (copolymerisation of ethylene and propylene). 1864 ml of liquid propylene are charged into the reactor described above. The reactor is thermostat-regulated at 40°C and saturated with ethylene until an overpressure of 6.1 bars is reached. The total pressure in the top of the reac¬tor was 21.6 bars. A hexane solution containing 2.65 mmoles of DEAC is then added and subsequently an aliquot of the catalyst containing 0.059 mmoles of Vanadium suspended in hexane and 0.176 mmoles of ETCA (molar ratio Al/V = 45, molar ratio ETCA/V = 3). The reaction is carried out at a constant tem¬perature feeding ethylene in continuous to keep the total pressure constant. After 60 minutes the reaction was practically exhausted. The mixture was left under stirring for a few minutes and then 1 bar of hydrogen was added. A hexane solution containing 2.36 mmoles of DEAC and 0.236 mmoles of ETCA was then added to the reactor (total molar ratio Al/V = 85, total molar ratio ETCA/V = 7). The polymerisation restarted (ethylene consump¬tion and exothermicity), and was carried out feed¬ing ethylene to maintain the total pressure constant. After 60 minutes from the beginning of the second polymerisation the monomers were evapo¬rated and the reactor was opened. 143 grams of polymer in agglomerated particles were recovered. The characterisations relating to this polymer are shown in table 1. EXAMPLES 4-6 These examples were carried out with the cata¬lyst Vanadium (III) acetylacetonate (examples 4 and 5) and with the catalyst based on supported Vana¬dium (example 6), Owing to the rapid deactivation of V(III) acetylacetonate, in examples 4 and 5 the components of the catalytic system are fed in small portions. In example 6 the Vanadium is introduced in a single portion together with the DEAC and the acti¬vator is then added. Comparative EXAMPLE 4 (copolymerisation of ethylene and propylene) 1925 ml of liquid propylene are charged into a perfectly anhydrous 2.8 dm2 pressure-resistant re¬actor equipped with a propeller stirrer. The reac¬tor is thermostat-regulated at 40°C and saturated with ethylene until an overpressure of 4.0 bars is reached. The total pressure in the top of the reactor was 19.5 bars. A hexane solution containing 4.22 mmoles of DEAC and a toluene solution of Vanadium (III) ace-tylacetonate containing 0.106 mmoles of Vanadium and 0.422 mmoles of ETCA are then charged into the reactor in small portions (total molar ratio Al/V = 40, total molar ratio ETCA/V =4). Ths reaction is carried out for 60 minutes at a constant temperature feeding ethylene in continuous to keep the total pressure constant. At the end of this period the reactor was opened and 17 5 g of polymer in the form of agglomerated particles were recovered. The characterisations relating to this polymer are shown in table 1. EXAMPLE 5 (copolymerisation of ethylene and propylene) 1925 ml of liquid propylene are charged into the perfectly anhydrous pressure-resistant reactor described above. The reactor is thermostat-regulated at 40°C and saturated with ethylene until an overpressure of 4.01 bars is reached. The total pressure in the top of the reactor was 19.5 bars. A hexane solution containing 4.7 mmoles of DEAC and a toluene solution containing 0.118 mmoles of Vanadium (III) acetylacetonate and 0.47 mmoles of ETCA are then charged into the reactor in small portions (molar ratio Al/V = 40, molar ratio ETCA/V = 4). The reaction is carried out at a constant tem¬perature feeding ethylene in continuous to keep the total pressure constant. After 60 minutes the reaction was practically exhausted. The mixture was left under stirring for a few minutes, 2 bars of hydrogen were then added and the mixture was saturated with a further 5 bars of ethylene (total ethylene pressure 5.51 bars). A hexane solution containing 4.7 mmoles of DEAC and 0.47 mmoles of ETCA was then added to the reac¬tor (total molar ratio Al/V = 80, total molar ratio ETCA/V = 8). The characterisations relating to this polymer are shown in table 1. EXAMPLES 6-7 In these examples a catalyst was used, prepared according to EP-A-717,050 of the same applicant, prepared with the same procedure as experimental example 6. Comparative EXAMPLE 6 (copolymerisation of ethylene and propylene). 1675 ml of liquid propylene are charged into a perfectly anhydrous 2.8 dm2 pressure-resistant re¬actor equipped with a propeller stirrer. The reac¬tor is thermostat-regulated at 40°C, saturated with ethylene until an overpressure of 6.0 bars is reached, and then a further overpressure of 0.1 bars of hydrogen was added. The total pressure in the top of the reactor was 21.6 bars. A hexane solution containing 4.32 mmoles of DEAC and subsequently an aliquot of the catalyst containing 0.086 mmoles of Vanadium suspended in hexane and 0.69 mmoles of ETCA are then charged into the reactor (molar ratio Al/V = 50, molar ra¬tio ETCA/V = 8) . The reaction is carried out for 60 minutes at a constant temperature feeding ethylene in continuous to keep the total pressure constant. At the end of this period the reactor was opened and 124 g of polymer in the form of agglomerated particles were recovered. The characterisations relating to this polymer are shown in table 1. EXAMPLE 7 (copolymerisation of ethylene and propylene) 1925 ml of liquid propylene are charged into a perfectly anhydrous 2.8 dm2 reactor equipped with a propeller stirrer. The reactor is thermostat-regulated at 40°C and saturated with ethylene until an overpressure of 4 bars is reached. The total pressure in the top of the reactor was 19.4 bars. A hexane solution containing 2.74 mmoles of DEAC is then added and subsequently an aliquot of the catalyst containing 0.068 mmoles of Vanadium suspended in hexane and 0.274 mmoles of ETCA (molar ratio Al/V = 40, molar ratio ETCA/V =4). The reaction is carried out at a constant tem¬perature feeding ethylene in continuous to keep the total pressure constant. After 60 minutes the reaction was practically exhausted. The mixture was left under stirring for a few minutes, 2 bars of hydrogen were then added and the mixture was then saturated with a further 2.5 bars of ethylene (total ethylene pressure = 6.5 bars). A hexane solution containing 2.74 mmoles of DEAC and 0.274 mmoles of ETCA was then added to the reactor {total molar ratio Al/V = 80, total molar ratio ETCA/V = 8). The polymerisation restarted (ethylene consump¬tion and exothermicity), and was carried out feeding ethylene to maintain the total pressure constant. After 60 minutes from the beginning of the second polymerisation the monomers were evapo¬rated and the reactor was opened. 192 grams of 5 polymer in agglomerated particles were recovered. The characterisations relating to this polymer are shown in table 1. From the data of table 1, the wider molecular weight distribution which can be obtained with the process of the present invention is evident. In order to give an evaluation of the process-ability of the polymer of example 2 with respect to the polymer of comparative example 1, the viscoe-lastic properties were studied {fig.l) in relation to the frequency of mechanical impulses received: the different behaviour of the sample relating to example 2, which at high frequency (corresponding to shears typical of processing and particularly extrusion) shows a much more marked drop in viscos¬ity with respect to the comparative sample, can be distinctly observed. WE CLAIM: 1. A process with two steps for the preparation in suspension of mixtures of ethylene-propylene (EPM) elastomer homopolymers or ethylene-propylene-diene (EPDM) elastomer terpolymers in the presence of a catalytic system essentially consisting of a compound of Vanadium, as such or supported on an inert carrier, and a cocatalyst essentially consisting of an Aluminum alkyl having the general formula RnAlXn, wherein R is a C1-C20 alkyl radical, X is a halogen, m+n = 3, m is an integer from 0 to 2, and in the presence of an activator, the above process being characterized in that: a) in the first step a first polymerisation of the monomers is carried out in the presence of the catalyst based on Vanadium, the cocatalyst and optionally in the presence of the activator, the molar ratio cocatalyst/Vanadium being from 5 to 500; up to a conversion degree of at least 1000 grams of polymer per gram of Vanadium, thus obtaining a suspension of the polymer in a liquid phase; b) in the second or subsequent steps further polymerisable monomers are added to the suspension of polymer obtained in step (a) together with further activator in order to have a molar ratio between activator, sum of the optional activator of step (a) and the activator of step (b), and Vanadium of from 4 to 50; and with further cocatalyst so as to have a ratio between the cocatalyst of step (b) and Vanadium of step (a) of from 5 to 500; the polymerisation reaction being continued up to a conversion of at least 3000 grams ofpolymer per gram of catalyst, 2. The process according to claim 1, wherein the catalyst based on Vanadium is selected from supported and/or prepolymerised catalysts based on Vanadium; Vanadyl trihalides, alkoxyhalides and alkoxides; Vanadium and Vanadyl acetylacetonates and chloro acetylacetonates. 3. The process according to claim 1, wherein the molar ratio cocatalyst/Vanadium in step (a) is from 7 to 50. 4. The process according to claim 1, wherein the ratio between the Aluminium of step (b) and Vanadium of step (a) is from 7 to 50. 5. The process according to claim 1, wherein m step (a) the molar ratio between activator and Vanadium is between 1 and 10. 6. The process according to claim 5, wherein in step (a) the molar ratio between activator and Vanadium is between 2 and 5. 7. The process according to claim 1, wherein in steps (a) and (b) the polymerisation temperature is from 15°C to 65°C and the pressure is from 8 to 80 bars. 8. The process according to claim 7, wherein the temperature is from 25°C to 50°C and the pressure from 12 to 40 bars. 9. The process according to claim 1, wherein steps (a) and (b) are both carried out in the presence of a molecular weight regulator. 10. The process according to claim 1, wherein step (a) is carried out without a molecular weight regulator, which is used however in step (b). 11. The process according to claims 9 and 10, wherein the molecular weight regulator is hydrogen. 12. The process according to claim 1, wherein the reaction medium consists of the same polymerizable monomers present in liquid phase. 13. The process according to claim 1, wherein the reaction medium consists of polymerizable monomers present in liquid phase, diluted with saturated hydrocarbons, preferably propane. 14. The process according to claim 1, wherein the number of steps is 2. 15. A process with two steps for the preparation in suspension of mixtures of ethylene-propylene (EPM) elastomer homopolymers or ethylene-propylene-diene (EPDM) elastomer terpolymers in the presence of a catalytic system substantially as herein described with reference to the accompanying drawings.

Documents:

715-mas-1997 abstract.pdf

715-mas-1997 claims duplicate.pdf

715-mas-1997 claims.pdf

715-mas-1997 correspondence others.pdf

715-mas-1997 correspondence po.pdf

715-mas-1997 description (complete) duplicate.pdf

715-mas-1997 description (complete).pdf

715-mas-1997 drawing.pdf

715-mas-1997 form-19.pdf

715-mas-1997 form-2.pdf

715-mas-1997 form-26.pdf

715-mas-1997 form-4.pdf

715-mas-1997 form-6.pdf

715-mas-1997 petition.pdf