Title of Invention	"AN IMPROVED PROCESS FOR THE PREPARATION OF OROMATIC POLYESTERS USING POLY (ARYL ESTER) PREPOLYMERS CONTAINING HYDROXYL AND ESTER GROUPS"
Abstract	This invention relates to an improved process for the preparation of aromatic polyesters. The present invention relates to an improved process for the preparation of high molecular weight (Mn 12,000-15,000) aromatic polyester. In the present process methyl alcohol is formed as a by product. Since methyl alcohol is a low boiling compound it can be removed conveniently and efficiently form the reactor. The recovered methyl alcohol can be effectively used. Poly(aryl ester) Prepolymers containing hydroxyl and ester groups have not been used in the prior art for preparation of aromatic polyester by solid state polycondensation technique. The high molecular weight aromatic polyester prepared by this process overcomes the drawbacks of hitherto known processes.

Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF OROMATIC POLYESTERS USING POLY (ARYL ESTER) PREPOLYMERS CONTAINING HYDROXYL AND ESTER GROUPS"

Abstract

This invention relates to an improved process for the preparation of aromatic polyesters. The present invention relates to an improved process for the preparation of high molecular weight (Mn 12,000-15,000) aromatic polyester. In the present process methyl alcohol is formed as a by product. Since methyl alcohol is a low boiling compound it can be removed conveniently and efficiently form the reactor. The recovered methyl alcohol can be effectively used. Poly(aryl ester) Prepolymers containing hydroxyl and ester groups have not been used in the prior art for preparation of aromatic polyester by solid state polycondensation technique. The high molecular weight aromatic polyester prepared by this process overcomes the drawbacks of hitherto known processes.

Full Text	This invention relates to an improved process for the preparation of aromatic polyesters. The present invention relates to an improved process for the preparation of aromatic polyester is based on dialkyl esters of aromatic dicarboxylic acids and dihydric phenols. The invention more particularly relates to an improved process for the preparation of high molecular weight (Mn 12,000-15,000) aromatic polyester. Aromatic polyesters are a class of polymers generally made from bisphenol(s) and aromatic diacid(s) particularly mixtures of terephthalic acid and isophthalic acid. These polyesters are high performance transparent thermoplastics with a good combination of thermal and mechanical properties. They are processed by injection molding, extrusion and film forming technique for its conversion to different types of useful products. Amorphous polyesters are generally prepared by melt polymerization. One such melt polymerization is the diacetate process. in the diacetate process, a dihydric phenol is converted to its diester derivative which is then reacted with an aromatic dicarboxylic acid to yield aromatic polyester. In this context references may be made to the following literature : U. S. Pat. Nos. 4,374,239; 4,386,186; 4,330,668; 4,485,230. Aromatic polyesters by diacetate process have a endency to be coloured which makes them unsuitable for many applications. Another problem associated with pro duction of aromatic polyesters by diacetate process is the formation of carboxylic acid as a by product, which is corrosive and requires special material for reactor construction. German offen DE 3,824,069 describes a variation of the diacetate process. In this process aromatic polyester is produced by reacting dialkyl esters of aromatic dicarbox-ylic acids with bisphenol-A diacetate in presence of a catalyst. Methyl acetate comes out as a by-product, however, it cannot be recycled in the process. U.S. Pat. No. 5,340,908 describes a process for the preparation of aromatic polyester by melt polymerization using alcoholysis route. This process comprises of two steps, the first step comprises of preparation of polyester prepolymer having intrinsic viscosity in the range of 0. 10 to 0.30 dL/g by reacting dimethyl esters of terephthalic acid and isophthalic acid with bisphenol-A in the melt phase in presence of solvent and catalyst. The second step consists of melt polymerization of purified polyarylate prepolymer in the presence of a catalyst. The drawback of the melt polymerization processes is that melt viscosities increase dramatically with increase in molecular weight, causing problems in agitation and heat transfer and consequent impact on product quality and process economics. Solid state po1ycondensation is a commonly practised technique to obtain high molecular weight crystalline polymers such as poly(ethy1ene terephthalate), nylon-6,6 etc. In this technique polycondensation is generally carried out by heating semicrystal1ine prepolymer. in a stream of inert gas or under vacuum at a temperature just below the polymer melting temperature. The salient features of solid state polycondensation are (1) The prepolymer is handled in powdered (or chips) form, thus the solid state polycondensation process requires a very simple reactor design, (25 The reaction temperatures employed are very much lower than that in melt polycondensation, hence a clean reaction is observed devoid of side reactions or thermal degradation, (3) Very high molecular weight polycondensates can be prepared, which are inaccessible through a melt process. The prior literature reports few variations of the diacetate process for the preparation of aromatic polyester by a solid state polycondensation of prepolymer. U.S. Pat. No. 3,684,766 discloses a process for copolyester by reacting bisphenol-A diacetate with terephth-alic acid and isophthalic acid. The resulting prepolymer was contacted with a crystallization medium. The crystallized prepolymer was heated in a fluidized bed, at a temperature below the melting point for certain period to achieve a copolyester having inherent viscosity of 0.50 or more. U.S. Pat. No. 4,314,051 describes a process for preparing crystalline prepolymer by reacting at least one diester derivative of a dihydric phenol with at least one aromatic dicarboxylic acid and then heating the prepolymer below its melting point to form a crystalline polyester having a reduced viscosity of 0.45 to 1.20 dL/g. U.S. Pat. No. 4,994,546 describes a process for the preparation of aromatic polyester from a prepolymer prepared by reacting bisphenol-A, acetic anhydride and atleast one aromatic dicarboxylic acid. The prepolymer is polycondensed under agitation to form a powdery solid which is further polymerized until the desired molecular weight is achieved. U.S. Pat. No. 5,164,478 discloses a process for the preparation of aromatic polyester having low colour wherein bisphenol-A, acetic anhydride, terephthalic acid and isophthalic acid are melt polymerized to form a prepolymer. The prepolymer is then treated with a crystallization medium and then further polymerized in the solid state by heating the prepolymer below its melting point under an inert gas flow. The prior art solid state polycondensation processes use prepolymers prepared by acidolysis of bisphenol-A diacetate by terephthalic acid and isophthalic acid. These prepolymers contain acetate and carboxylic end groups which react further under solid state po1ycondesation conditions yielding high molecular weight polyester with the formation of acetic acid as a by-product. The disadvantage of the above process is that it is not easy to remove acetic acid. Furthermore, acetic acid handling requires equipments with special materials of construction. Furthermore presence of traces of acetic acid in the product may affect the thermal stability of the polyester. Another object of the present invention is to provide an improved process for the preparation of aromatic polyesters employing poly(ary1 ester) prepolymer containing dialkyl and ester groups. Accordingly, the present invention provides an improved process for the preparation of aromatic polyesters by the use of poly(ary1 ester) prepolymer which contains hydroxyl and ester end groups employing solid state poly condensation yielding high molecular weight (tin = 12,000 - 15, 000) aromatic polyester. In the present process methyl alcohol is formed as a by product. Since methyl alcohol is a low boiling compound it can be removed conveniently and efficiently from the reactor. The recovered methyl alcohol can be effectively used. Poly(ary1 ester) Prepolymers containing hydroxyl and ester groups have not been used in the prior art for prepara tion of aromatic polyester by solid state polyconden- sation technique. The main objective of the present invention is therefore to provide an improved process for the preparation of high molecular weight aromatic polyester overcoming the drawbacks of hitherto known processes. Accordingly, the present invention provides an improved process for the preparation of aromatic polyesters using poly (aryl ester) prepolymers containing hydroxyl and ester groups which comprises; a) melt polymerising dialkyl esters of aromatic dicarboxylic acid such as herein described with aromatic bisphenol as herein described in presence of a catalyst selected from metals of group IVB, metal alkoxides and group IVA metals and their derivatives such as dibutyl tin diesters, tin phenoxide, silicon phenoxide in the range of 0.05 to 0.5 wt% of prepolymer to obtain an amorphous poly(aryl ester) prepolymer containing hydroxyl and ester groups, b) crystallizing the poly (aryl ester) prepolymer as obtained in step a) by suspending in a diluent as herein described, heating at a reflux temperature in the range of 60-150°C for a period of 2 to 4 hours, c) separating the crystallized poly(aryl ester) prepolymer by known methods, drying the said crystallized prepolymer at 70-80°C at vacuum 1 mm Hg, d) heating the crystallized poly(aryl ester) prepolymer initially at atmospheric pressure and then in the pressure range of 0.1 to 10mm Hg at a temperature in the range of 200-25 0°C or by heating in a fluidized bed at a temperature below the melting point of the polymer in an inert gas, e) cooling the poly (aryl ester) to room temperature to obtain desired product. During the heating stage, the poly(arylester) prepolymer undergoes further polymerization in the solid state with an increase in molecular weight. The process of the present invention thus obviates the drawbacks of the prior art processes for the preparation the drawbacks of the prior art processes for the preparation poly(aryl ester) from dialkyl esters of aromatic dicarboxylic acids and aromatic bisphenols. In one the embodiments of the present invention the prepolymer suitable for the process is generally amorphous and has an intrinsic viscosity of approximately 0.20 - 0.30 dL /g corresponding to number average molecular weight in the range of 2,800 - 6,000. In another embodiment of the invention, the poly (aryl ester) prepolymer can be prepared by melt polyconden- sation process as described in U.S. Pat. No. 5,340,908 by reacting esters of aromatic dicarboxylic acids with aromatic bisphenol(s) in presence of a catalyst. These poly(ary1ester) prepolymers do not show any crystalline peak either in Differential Scanning Calorimetry (DSC) or X-ray diffraction (XRD) and hence termed amorphous. In another embodiment of the present invention the dialkyl esters employable may be dimethyl terephtha1 ate, dimethyl isophthalate and mixtures thereof, as well as 2,6-naphthalene dicarboxylic acid esters and alkyl substituted homologs of such dicarboxylic acid esters wherein the alkyl group contain 1 to 4 carbon atoms. In yet another embodiment the bisphenol employable may be bisphenol-A, halo substituted bisphenol-A, alkyl-substituted bisphenol-A, hydroquinone, resorcinol and various types of other polyphenols. In yet another embodiment the catalyst employed may include alkoxides of Gt IVB metals and derivatives of Gr 1VA metals. The diluents used can be chosen from organic compounds such as ethyl acetate, acetone, toluene or xylene or combinations thereof or the like. The diluent may be any solvent that will promote crystallization but not dissolve the poly(ary1 ester) prepolymer. The heterogeneous mixture of poly(aryIester) prepolymer and the diluent is then heated to the respective refluxing temperatures. The optimum temperature and time for crystallization will depend upon the nature of the diluent. Subsequently the diluent is removed by distillation and the o product is dried in vacuum at 70 - 80 C for 3-4 hours. The dried poly(ary1 ester) prepolymers show appreciable crystal- linity as observed by the appearance of crystalline melting o peaks in DSC in the range of 190 to 250 C. The catalyst employed may be dibutyltin diesters, tin phenoxide, silicon phenoxide etc. The amount of catalyst employed may be in the range of 0.05 to 0.50 weight percent based on prepoiymer. The crystallized po1y(ary1ester) prepoiymer may be post-polymer ized in solid state at different pressures ranging from atmospheric pressure to sub-atmospheric pressure. Generally 1 atm (760 mm, Hg) is maintained during the initial phase and subsequently the pressure is reduced to 1.0 to 0.1 mm, Hg or even lower. The temperature of the reac- o tion may be in the range of 170 - 240 C. The heating time may be between 8-15 hours, depending on the molecular weight range desired. Alternatively the crystallized poly(ary1 ester) prepoiymer • can be heated in a fluidized bed at a temperature below the melting point of the polymer using a hot inert gas for a period of time which is sufficient to achieve an intrinsic viscosity of 0.60 dL/g. The inert gas can be chosen amongst nitrogen, argon, carbon dioxide or helium. The process of the present invention is described herein below by examples which are illustrative only and should not be construed to limit the scope of the present invention, in any manner. EXAMPLE 1 A prepolymer (1 g, having intrinsic velocity [n3 = 0.20 dL/g in chloroform at 30 C) was taken in 100 mL round bottomed -4 flask along with 25 mL ethyl acetate and 5X10 g of dibutyl- o tin dilaurate and refluxed at 80 - 90 C for 4 hours. Thereafter the ethyl acetate was removed by distillation and the poly(arylester) prepolymer dried in vacuum (1 mm, Hg) at o 70 - 80 C. The poly(ary1 ester) prepolymer was mechanically crushed and particles passing through 22 mesh screen was collected. 0.75 g of this poly(ary1 ester) prepolymer was o heated to 170 C under nitrogen over a period of 1 hour. Thereafter the pressure was reduced to 1mm, Hg and the prepoly- o mer was held at 170 C for 5 hours at the first instance and o o o 2 hours each at 200 C, 2.20 C and 240 C respectively. Subsequently the poly(ary1 ester) was cooled to room temperature. The resulting poly(ary1 ester) had intrinsic viscosity Cn3 of o 0.35 dL/g at 30 C in chloroform. EXAMPLE 2 A poly(ary1 ester) prepolymer (1 g, having intrinsic o velocity [n] = 0.20 dL/g in chloroform at 30 C) was taken in 100 aL round bottomed flask along with 25 mL ethyl acetate -4 and 5X10 g of dibutyltin dilaurate and refluxed at 80- o 90 C for 4 hours.' Thereafter the ethyl acetate was removed by distillation and the poly(arylester) prepolymer dried in o vacuum (1 mm. Hgl at 70 - 80 C. The poIy(arylester) prepol- vmer was mechanically crushed and particles passing through 22 mesh screen was collected. 0.75 g of po1y(ary1ester) pre- o polymer was heated to 170 C under nitrogen over a period of 1 hour. There- after the pressure was reduced to imm, Hg and o the prepoly mer was held at 170 C for 5 hours at the first o o o instance and 2 hours each at 200 C. 220 C and 240 C. Subsequently the po)y(ary1ester! was cooled to room temperature. The resultins polyfarylester) had intrinsic v iscosity [n] of 0.54 o d L lg at 30 ºC in chloroform. EXAMPLE 3 A poly(arv1ester) prepolyraer (1 g having intrinsic o velocity. In] = 0.20 dL/g in chloroform at 30 C) was taken in LOO mL round bottomed flask along with 25 mL acetone and 5 X -4 ' o 10 g of dibutyltin dilaurate and ref luxed at 60 - 70 C for 4 hours. Thereafter the acetone was removed by distillation and the polv(arylester) prepolyraer dried in vacuum o (1mm. HG) at 70 - 80 C. The po 1 y ( ary1ester ) prepolymer was mecha.ni cally crushed and particles passing through 22 mesh screen was collected. 0.75 g of poly(ary1esfcer) prepolyraer o was heated to 170 C under nitrogen over a period of 1 hour. Thereafter the pressure was reduced to 1 mm, Hg o and the poly(ary1ester) prepolymer was held at 170 C for o 5 hours at the first instance and 2 hours each at 180 C. o o o 200 C, 220 C and 240 C. Subsequently the poly(ary1 ester) • was cooled to room temperature. The resulting po1y(ary1 ester) had intrinsic o viscosity [n] of 0.50 dL/g at 30 C in chloroform. EXAMPLE 4 A poly(arylester) prepolymer (1 g, having intrinsic o velocity [n] = 0.30 dL/g in chloroform at 30 C) was taken in 100 mL round bottomed flask along with 25 mL toluene and 5 -4 X 10 g of dibutyltin dilaurate and refluxed at 110 o 120 C for 4 hours. Thereafter the toluene was removed by distillation and the po1y(ary1ester) prepolymer o dried in vacuum (1mm, Hg) at 70- 80 C. The po1y(ary1ester) prepolymer was mechanically crushed and particles passing through 22 mesh screen was collected. 0.75 g of o po1y(ary1 ester) prepolymer was heated to 200 C under nitrogen over a period of 1 hour. Thereafter the pressure was reduced to 1 mm, Hg and the po1y(ary1ester) prepolymer o was held at 200 C for 5 hours at the first instance and o o o 2 hours each at 220 C, 240 C and 250 C. Subsequently the po1y(ary1ester) was cooled to room tempera ture. The resulting po1y(ary1 ester) had intrinsic viscosity Cn3 of 0.60 o dL/g at 30 C in chloroform. EXAMPLE 5 A po1y(ary1 ester) prepolymer (1 g,having intrinsic o velocity [nl = 0.30 dL/g in chloroform at 30 C) was taken in 100 mL round bottomed flask along with 25 mL xylene and -4 5X10 g of dibutyltin dilaurate and refluxed at 140 - o 150 C for 4 hours. Thereafter the toluene was removed by distillation and the poly(arylester) prepolymer dried in vacuum o (1 ram, Hg) at 70 - 80 C. The po1y(ary1 ester) prepolymer was mechanically crushed and particles passing through 22 mesh screen was collected. 0.75 g of poly(ary1ester) prepoly- o raer was heated to 2:00 C under nitrogen over a period of 1 hour. Thereafter the pres sure was reduced to 1 ram, Hg and the o poly(ary1 ester) prepolymer was held at 200 C for 5 hours at o o the first instance and 2 hours each at 220 C, 240 C and o 250 C. Subsequently the poly(ary1 ester) was cooled to room temperature. The resulting poly(ary1 ester) had intrinsic o viscosity Cn3 of 0.55 dL/g at 30 C in chloroform. The aain advantages of the invention are : The present process uses the po1y(arylester) prepolymer prepared by alcoholysis of aromatic bisphenol(s) by dialkyl esters of aromatic dicarboxylic acid(s). Unlike the poly(ary1ester) prepolymer prepared by acidolysis of bisphenol(s) diacetate by aromatic dicarboxylic acid(s), the poly(ary1ester) prepolymer prepared by alcoholysis route is free from residual by-product as the by-product (methyl alcohol) being the low boiling compound is removed efficiently and conveniently. Hence allows the production of better quality prepolymer. High molecular weight polyesters can be produced by solid state polycon densation of these poly(ary1ester) prepolymers without any need of operations such as premelting, efficient agitation etc. Aromatic polyester melts have high viscosities and hence cannot be agitated easily to provide uniform heating and local over heating cause the melt to degrade. On the contrary, solid state polymerization does not require agitation hence there is no danger of polymer degradation and consequently poly(ary1ester) with good colour is obtained. Poly(ary1ester)s of any desired molecular weights can be produced for end applications such as injection molding or extrusion simply by controlling the time temperature profile. Claim: 1. An improved process for the preparation of aromatic polyesters using poly (aryl ester) prepolymers containing hydroxyl and ester groups which comprises; a) melt polymerising dialkyl esters of aromatic dicarboxylic acid such as herein described with aromatic bisphenol as herein described in presence of a catalyst selected from metals of group IVB, metal alkoxides and group IVA metals and their derivatives such as dibutyl tin diesters, tin phenoxide, silicon phenoxide in the range of 0.05 to 0.5 wt% of prepolymer to obtain an amorphous poly(aryl ester) prepolymer containing hydroxyl and ester groups, b) crystallizing the poly (aryl ester) prepolymer as obtained in step a) by suspending in a diluent as herein described, heating at a reflux temperature in the range of 60-150°C for a period of 2 to 4 hours, c) separating the crystallized poly(aryl ester) prepolymer by known methods , drying the said crystallized prepolymer at 70-80°C at vacuum 1 mm Hg, d) heating the crystallized poly(aryl ester) prepolymer initially at atmospheric pressure and then in the pressure range of 0.1 to 10mm Hg at a temperature in the range of 200-250°C or by heating in a fluidized bed at a temperature below the melting point of the polymer in an inert gas, e) cooling the poly (aryl ester) to room temperature to obtain desired product. 2. An improved process as claimed in claim 1 wherein the diluents such as ethyl acetate, acetone, toluene, xylene are used in step (b). 3. An improved process as claimed in claim 1 wherein the inert gas used is selected from nitrogen, argon, CO2 & helium. 4. An improved process for the prepjaration of aromatic polyesters using poly (arylester) prepolyrriers containing hydroxuyl and ester groups as fully described herein;with reference to the examples contauned therein

Full Text

This invention relates to an improved process for the preparation of aromatic polyesters. The present invention relates to an improved process for the preparation of aromatic polyester is based on dialkyl esters of aromatic dicarboxylic acids and dihydric phenols. The invention more particularly relates to an improved process for the preparation of high molecular weight (Mn 12,000-15,000) aromatic polyester.
Aromatic polyesters are a class of polymers generally made from bisphenol(s) and aromatic diacid(s) particularly mixtures of terephthalic acid and isophthalic acid. These polyesters are high performance transparent thermoplastics with a good combination of thermal and mechanical properties. They are processed by injection molding, extrusion and film forming technique for its conversion to different types of useful products.
Amorphous polyesters are generally prepared by melt polymerization. One such melt polymerization is the diacetate process. in the diacetate process, a dihydric phenol is converted to its diester derivative which is then reacted with an aromatic dicarboxylic acid to yield aromatic polyester.
In this context references may be made to the
following literature : U. S. Pat. Nos. 4,374,239;
4,386,186; 4,330,668; 4,485,230.
Aromatic polyesters by diacetate process have a
endency to be coloured which makes them unsuitable for
many applications. Another problem associated with pro
duction of aromatic polyesters by diacetate
process is the formation of carboxylic acid as a by
product, which is corrosive and requires special material
for reactor construction.
German offen DE 3,824,069 describes a variation of the diacetate process. In this process aromatic polyester is produced by reacting dialkyl esters of aromatic dicarbox-ylic acids with bisphenol-A diacetate in presence of a catalyst. Methyl acetate comes out as a by-product, however, it cannot be recycled in the process.
U.S. Pat. No. 5,340,908 describes a process for the preparation of aromatic polyester by melt polymerization using alcoholysis route. This process comprises of two steps, the first step comprises of preparation of polyester prepolymer having intrinsic viscosity in the range of 0. 10 to 0.30 dL/g by reacting dimethyl esters of terephthalic acid and isophthalic acid with bisphenol-A in the melt phase in presence of solvent and catalyst. The second step consists of melt polymerization of purified polyarylate prepolymer in the presence of a catalyst.
The drawback of the melt polymerization processes is that melt viscosities increase dramatically with increase in molecular weight, causing problems in agitation and heat transfer and consequent impact on product quality and process economics.
Solid state po1ycondensation is a commonly practised technique to obtain high molecular weight crystalline polymers such as poly(ethy1ene terephthalate), nylon-6,6 etc. In this technique polycondensation is generally carried out by heating semicrystal1ine prepolymer. in a stream of inert gas or under vacuum at a temperature just below the polymer melting temperature. The salient features of solid state polycondensation are (1) The prepolymer is handled in powdered (or chips) form, thus the solid state polycondensation process requires a very simple reactor design, (25 The reaction temperatures employed are very much lower than that in melt polycondensation, hence a clean reaction is observed devoid of side reactions or thermal degradation, (3) Very high molecular weight polycondensates can be prepared, which are inaccessible through a melt process.
The prior literature reports few variations of the diacetate process for the preparation of aromatic polyester by a solid state polycondensation of prepolymer.
U.S. Pat. No. 3,684,766 discloses a process for copolyester by reacting bisphenol-A diacetate with terephth-alic acid and isophthalic acid. The resulting prepolymer was contacted with a crystallization medium. The crystallized prepolymer was heated in a fluidized bed, at a temperature below the melting point for certain period to achieve a copolyester having inherent viscosity of 0.50 or more.
U.S. Pat. No. 4,314,051 describes a process for preparing crystalline prepolymer by reacting at least one
diester derivative of a dihydric phenol with at least one aromatic dicarboxylic acid and then heating the prepolymer below its melting point to form a crystalline polyester having a reduced viscosity of 0.45 to 1.20 dL/g.
U.S. Pat. No. 4,994,546 describes a process for the preparation of aromatic polyester from a prepolymer prepared by reacting bisphenol-A, acetic anhydride and atleast one aromatic dicarboxylic acid. The prepolymer is polycondensed under agitation to form a powdery solid which is further polymerized until the desired molecular weight is achieved.
U.S. Pat. No. 5,164,478 discloses a process for the preparation of aromatic polyester having low colour wherein bisphenol-A, acetic anhydride, terephthalic acid and isophthalic acid are melt polymerized to form a prepolymer. The prepolymer is then treated with a crystallization medium and then further polymerized in the solid state by heating the prepolymer below its melting point under an inert gas flow.
The prior art solid state polycondensation processes use prepolymers prepared by acidolysis of bisphenol-A diacetate by terephthalic acid and isophthalic acid. These prepolymers contain acetate and carboxylic end groups which react further under solid state po1ycondesation conditions yielding high molecular weight polyester with the formation of acetic acid as a by-product. The disadvantage of the above process is that it is not easy to remove
acetic acid. Furthermore, acetic acid handling requires equipments with special materials of construction. Furthermore presence of traces of acetic acid in the product may affect the thermal stability of the polyester.
Another object of the present invention is to provide an improved process for the preparation of aromatic polyesters employing poly(ary1 ester) prepolymer containing dialkyl and ester groups.
Accordingly, the present invention provides an improved process for the preparation of aromatic polyesters by the use of poly(ary1 ester) prepolymer which contains hydroxyl and ester end groups employing solid state poly condensation yielding high molecular weight (tin = 12,000 - 15, 000) aromatic polyester.
In the present process methyl alcohol is formed as a by product. Since methyl alcohol is a low boiling compound it can be removed conveniently and efficiently from the reactor. The recovered methyl alcohol can be effectively used.
Poly(ary1 ester) Prepolymers containing hydroxyl and
ester groups have not been used in the prior art for prepara
tion of aromatic polyester by solid state polyconden-
sation technique.
The main objective of the present invention is therefore to provide an improved process for the preparation of high molecular weight aromatic polyester overcoming the drawbacks of hitherto known processes.
Accordingly, the present invention provides an improved process for the preparation of aromatic polyesters using poly (aryl ester) prepolymers containing hydroxyl and ester groups which comprises;
a) melt polymerising dialkyl esters of aromatic dicarboxylic acid such as herein described with aromatic bisphenol as herein described in presence of a catalyst selected from metals of group IVB, metal alkoxides and group IVA metals and their derivatives such as dibutyl tin diesters, tin phenoxide, silicon phenoxide in the range of 0.05 to 0.5 wt% of prepolymer to obtain an amorphous poly(aryl ester) prepolymer containing hydroxyl and ester groups,
b) crystallizing the poly (aryl ester) prepolymer as obtained in step a) by suspending in a diluent as herein described, heating at a reflux temperature in the range of 60-150°C for a period of 2 to 4 hours,
c) separating the crystallized poly(aryl ester) prepolymer by known methods, drying the said crystallized prepolymer at 70-80°C at vacuum 1 mm Hg,
d) heating the crystallized poly(aryl ester) prepolymer initially at atmospheric pressure and then in the pressure range of 0.1 to 10mm Hg at a temperature in the range of 200-25 0°C or by heating in a fluidized bed at a temperature below the melting point of the polymer in an inert gas,
e) cooling the poly (aryl ester) to room temperature to obtain desired product.
During the heating stage, the poly(arylester) prepolymer undergoes further polymerization in the solid state with an increase in molecular weight.
The process of the present invention thus obviates the drawbacks of the prior art processes for the preparation the drawbacks of the prior art processes for the preparation poly(aryl ester) from dialkyl esters of aromatic dicarboxylic acids and aromatic bisphenols.
In one the embodiments of the present invention the prepolymer suitable for the process is generally amorphous and has an intrinsic viscosity of approximately 0.20 - 0.30 dL /g corresponding to number average molecular weight in the range of 2,800 - 6,000.
In another embodiment of the invention, the
poly (aryl ester) prepolymer can be prepared by melt polyconden-
sation process as described in U.S. Pat. No. 5,340,908 by reacting esters of aromatic dicarboxylic acids with aromatic bisphenol(s) in presence of a catalyst.
These poly(ary1ester) prepolymers do not show any crystalline peak either in Differential Scanning Calorimetry (DSC) or X-ray diffraction (XRD) and hence termed amorphous.
In another embodiment of the present invention the dialkyl esters employable may be dimethyl terephtha1 ate, dimethyl isophthalate and mixtures thereof, as well as 2,6-naphthalene dicarboxylic acid esters and alkyl substituted homologs of such dicarboxylic acid esters wherein the alkyl group contain 1 to 4 carbon atoms.
In yet another embodiment the bisphenol employable may be bisphenol-A, halo substituted bisphenol-A, alkyl-substituted bisphenol-A, hydroquinone, resorcinol and various types of other polyphenols.
In yet another embodiment the catalyst employed may include alkoxides of Gt IVB metals and derivatives of Gr 1VA metals.
The diluents used can be chosen from organic compounds such as ethyl acetate, acetone, toluene or xylene or combinations thereof or the like. The diluent may be any solvent that will promote crystallization but not dissolve the poly(ary1 ester) prepolymer. The heterogeneous mixture of poly(aryIester) prepolymer and the diluent is then heated to the respective refluxing
temperatures. The optimum temperature and time for crystallization will depend upon the nature of the diluent. Subsequently the diluent is removed by distillation and the
o product is dried in vacuum at 70 - 80 C for 3-4 hours. The
dried poly(ary1 ester) prepolymers show appreciable crystal-
linity as observed by the appearance of crystalline melting
o peaks in DSC in the range of 190 to 250 C. The catalyst
employed may be dibutyltin diesters, tin phenoxide, silicon
phenoxide etc. The amount of catalyst employed may be in the
range of 0.05 to 0.50 weight percent based on prepoiymer.
The crystallized po1y(ary1ester) prepoiymer may be post-polymer ized in solid state at different pressures ranging from atmospheric pressure to sub-atmospheric pressure. Generally 1 atm (760 mm, Hg) is maintained during the initial phase and subsequently the pressure is reduced to 1.0
to 0.1 mm, Hg or even lower. The temperature of the reac-
o tion may be in the range of 170 - 240 C.
The heating time may be between 8-15 hours, depending on
the molecular weight range desired.
Alternatively the crystallized poly(ary1 ester) prepoiymer • can be heated in a fluidized bed at a temperature below the melting point of the polymer using a hot inert gas for a period of time which is sufficient to achieve an intrinsic viscosity of 0.60 dL/g. The inert gas can be chosen amongst nitrogen, argon, carbon dioxide or helium.
The process of the present invention is described herein below by examples which are illustrative only and should not be construed to limit the scope of the present invention, in any manner.
EXAMPLE 1
A prepolymer (1 g, having intrinsic velocity [n3 = 0.20
dL/g in chloroform at 30 C) was taken in 100 mL round bottomed
-4 flask along with 25 mL ethyl acetate and 5X10 g of dibutyl-
o tin dilaurate and refluxed at 80 - 90 C for 4 hours.
Thereafter the ethyl acetate was removed by distillation and
the poly(arylester) prepolymer dried in vacuum (1 mm, Hg) at
o 70 - 80 C. The poly(ary1 ester) prepolymer was mechanically
crushed and particles passing through 22 mesh screen was
collected. 0.75 g of this poly(ary1 ester) prepolymer was
o heated to 170 C under nitrogen over a period of 1 hour.
Thereafter the pressure was reduced to 1mm, Hg and the prepoly-
o mer was held at 170 C for 5 hours at the first instance and
o o o
2 hours each at 200 C, 2.20 C and 240 C respectively. Subsequently the poly(ary1 ester) was cooled to room temperature.
The resulting poly(ary1 ester) had intrinsic viscosity Cn3 of
o 0.35 dL/g at 30 C in chloroform.
EXAMPLE 2
A poly(ary1 ester) prepolymer (1 g, having intrinsic
o velocity [n] = 0.20 dL/g in chloroform at 30 C) was taken in
100 aL round bottomed flask along with 25 mL ethyl acetate
-4 and 5X10 g of dibutyltin dilaurate and refluxed at 80-
o
90 C for 4 hours.' Thereafter the ethyl acetate was removed
by distillation and the poly(arylester) prepolymer dried in
o vacuum (1 mm. Hgl at 70 - 80 C. The poIy(arylester) prepol-
vmer was mechanically crushed and particles passing through
22 mesh screen was collected. 0.75 g of po1y(ary1ester) pre-
o polymer was heated to 170 C under nitrogen over a period of
1 hour. There- after the pressure was reduced to imm, Hg and
o the prepoly mer was held at 170 C for 5 hours at the first
o o o
instance and 2 hours each at 200 C. 220 C and 240 C. Subsequently the po)y(ary1ester! was cooled to room temperature. The
resultins polyfarylester) had intrinsic v iscosity [n] of 0.54
o d L lg at 30 ºC in chloroform.
EXAMPLE 3
A poly(arv1ester) prepolyraer (1 g having intrinsic
o velocity. In] = 0.20 dL/g in chloroform at 30 C) was taken in
LOO mL round bottomed flask along with 25 mL acetone and 5 X
-4 ' o
10 g of dibutyltin dilaurate and ref luxed at 60 - 70 C
for 4 hours. Thereafter the acetone was removed by distillation and the polv(arylester) prepolyraer dried in vacuum
o
(1mm. HG) at 70 - 80 C. The po 1 y ( ary1ester ) prepolymer was
mecha.ni cally crushed and particles passing through 22 mesh
screen was collected. 0.75 g of poly(ary1esfcer) prepolyraer
o was heated to 170 C under nitrogen over a period of 1
hour. Thereafter the pressure was reduced to 1 mm, Hg
o and the poly(ary1ester) prepolymer was held at 170 C for
o 5 hours at the first instance and 2 hours each at 180 C.
o o o
200 C, 220 C and 240 C.
Subsequently the poly(ary1 ester) • was cooled to room
temperature. The resulting po1y(ary1 ester) had intrinsic
o viscosity [n] of 0.50 dL/g at 30 C in chloroform.
EXAMPLE 4
A poly(arylester) prepolymer (1 g, having intrinsic
o velocity [n] = 0.30 dL/g in chloroform at 30 C) was taken in
100 mL round bottomed flask along with 25 mL toluene and 5
-4 X 10 g of dibutyltin dilaurate and refluxed at 110
o
120 C for 4 hours. Thereafter the toluene was
removed by distillation and the po1y(ary1ester) prepolymer
o dried in vacuum (1mm, Hg) at 70- 80 C. The po1y(ary1ester)
prepolymer was mechanically crushed and particles passing
through 22 mesh screen was collected. 0.75 g of
o po1y(ary1 ester) prepolymer was heated to 200 C under
nitrogen over a period of 1 hour. Thereafter the pressure
was reduced to 1 mm, Hg and the po1y(ary1ester) prepolymer
o was held at 200 C for 5 hours at the first instance and
o o o
2 hours each at 220 C, 240 C and 250 C. Subsequently
the po1y(ary1ester) was cooled to room tempera ture. The
resulting po1y(ary1 ester) had intrinsic viscosity Cn3 of 0.60
o dL/g at 30 C in chloroform.
EXAMPLE 5
A po1y(ary1 ester) prepolymer (1 g,having intrinsic
o velocity [nl = 0.30 dL/g in chloroform at 30 C) was taken in
100 mL round bottomed flask along with 25 mL xylene and
-4 5X10 g of dibutyltin dilaurate and refluxed at 140 -
o 150 C for 4 hours. Thereafter the toluene was removed by distillation and the poly(arylester) prepolymer dried in vacuum
o (1 ram, Hg) at 70 - 80 C. The po1y(ary1 ester) prepolymer was
mechanically crushed and particles passing through 22 mesh
screen was collected. 0.75 g of poly(ary1ester) prepoly-
o raer was heated to 2:00 C under nitrogen over a period of 1
hour. Thereafter the pres sure was reduced to 1 ram, Hg and the
o
poly(ary1 ester) prepolymer was held at 200 C for 5 hours at
o o
the first instance and 2 hours each at 220 C, 240 C and
o
250 C. Subsequently the poly(ary1 ester) was cooled to
room temperature. The resulting poly(ary1 ester) had intrinsic
o viscosity Cn3 of 0.55 dL/g at 30 C in chloroform.
The aain advantages of the invention are :
The present process uses the po1y(arylester) prepolymer prepared by alcoholysis of aromatic bisphenol(s) by dialkyl esters of aromatic dicarboxylic acid(s). Unlike the poly(ary1ester) prepolymer prepared by acidolysis of bisphenol(s) diacetate by aromatic dicarboxylic acid(s), the poly(ary1ester) prepolymer prepared by alcoholysis route is free from residual by-product as the by-product (methyl alcohol) being the low boiling compound is removed efficiently and conveniently. Hence allows the production of better quality prepolymer. High molecular weight polyesters can be produced by solid state polycon densation of these poly(ary1ester) prepolymers without any need of operations such as premelting, efficient agitation etc.
Aromatic polyester melts have high viscosities and hence cannot be agitated easily to provide uniform heating and local over heating cause the melt to degrade. On the contrary, solid state polymerization does not require agitation hence there is no danger of polymer degradation and consequently poly(ary1ester) with good colour is obtained. Poly(ary1ester)s of any desired molecular weights can be produced for end applications such as injection molding or extrusion simply by controlling the time temperature profile.

Claim:
1. An improved process for the preparation of aromatic polyesters using poly (aryl
ester) prepolymers containing hydroxyl and ester groups which comprises;
a) melt polymerising dialkyl esters of aromatic dicarboxylic acid such as herein described with aromatic bisphenol as herein described in presence of a catalyst selected from metals of group IVB, metal alkoxides and group IVA metals and their derivatives such as dibutyl tin diesters, tin phenoxide, silicon phenoxide in the range of 0.05 to 0.5 wt% of prepolymer to obtain an amorphous poly(aryl ester) prepolymer containing hydroxyl and ester groups,
b) crystallizing the poly (aryl ester) prepolymer as obtained in step a) by suspending in a diluent as herein described, heating at a reflux temperature in the range of 60-150°C for a period of 2 to 4 hours,
c) separating the crystallized poly(aryl ester) prepolymer by known methods , drying the said crystallized prepolymer at 70-80°C at vacuum 1 mm Hg,
d) heating the crystallized poly(aryl ester) prepolymer initially at atmospheric pressure and then in the pressure range of 0.1 to 10mm Hg at a temperature in the range of 200-250°C or by heating in a fluidized bed at a temperature below the melting point of the polymer in an inert gas,
e) cooling the poly (aryl ester) to room temperature to obtain desired product.

2. An improved process as claimed in claim 1 wherein the diluents such as ethyl acetate, acetone, toluene, xylene are used in step (b).
3. An improved process as claimed in claim 1 wherein the inert gas used is selected from nitrogen, argon, CO2 & helium.
4. An improved process for the prepjaration of aromatic polyesters using poly (arylester) prepolyrriers containing hydroxuyl and ester groups as fully described herein;with reference to the examples contauned therein

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Patent Number

232152

Indian Patent Application Number

2475/DEL/1995

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

15-Mar-2009

Date of Filing

29-Dec-1995

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	SUDHAKAR SADASHIV MAHAJAN	NATIONAL CHEMICAL LABORATORY, PUNE -411 008, INDIA.
2	SWAMINATHAN SIVARAM	NATIONAL CHEMICAL LABORATORY, PUNE -411 008, INDIA.
3	BHAKSKAR BHAIRAVNATH IDAGE	NATIONAL CHEMICAL LABORATORY, PUNE -411 008, INDIA.

PCT International Classification Number

C08G 63/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA