DE2365934A1 - Polyesters from butane diol-1,4 and phthalic acids - by transesterifying under pressure to minimise formation of tetrahydrofuran - Google Patents

Abstract

High m.wt. polyesters suitable for injection moulding are prepd. by condensing butanediol-(1,4) opt.mixed with =10 mole % of another diol with dialkyl esters of tereand/or iso-phthalic acids opt. mixed with is not >10 moles % other dialkyl esters of dicarboxylic acid, the transesterification being effected under pressure as an improvement. Pref. the stage comprises (1) transesterifying 1 mole of the ester with 1.05-1.9 mole diol using 0.01-0.4% catalyst (based on ester) under 2-10 bars at 180-230 degrees C, (2) polycondensing the prodt. from (1) at 230-300 degrees C under 0.1-5 mm.Hg pressure in the molten state, and (3) further condensing the polyester from (2) under reduced pressure or inert atm. at 5-50 degrees C lower than the polyester m.pt. until an intrinsic viscosity of 0.6-1.9dl./g. is reached. Formation of tetrahydrofuran in the transesterification stage is considerably reduced, amt. of oligo-esters is reduced and the polyesters have higher m.wt.

Description

Bayer Aktiengesellschaft

Central area of patents, trademarks and licenses

509 Leverkusen. Bayerwerk

^{Pv / Gi} 2 July 1, 1976

Manufacture of high molecular weight polyesters of butanediol (1,4)

The invention relates to the continuous production of high molecular weight polyesters or copolyesters from dialkyl esters of terephthalic acid or isophthalic acid and butanediol- (1,4).

Polybutylene terephthalate and polybutylene isophthalate are known per se. These polyesters are mostly made by dialkyl esters of terephthalic or isophthalic acid at low temperatures with butanediol (1,4) to give the corresponding Bis-co-hydroxybutyl esters and then transesterified condensed at higher temperatures with elimination of butylene glycol- (1,4) in the melt to form the polyester. Often it is necessary to post-condense the polyesters obtained below their melting point in order to increase the molecular weight. Only the post-condensed polyesters are suitable for the production of high-quality moldings by injection molding or extrusion.

In the transesterification of terephthalic acid or isophthalic acid dialkyl esters with butanediol (1,4), tetrahydrofuran is formed as a by-product through cyclizing dehydration of the butanediol. In this side reaction, up to about 2o %

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of the butanediol used are lost. It has therefore been proposed ^ (cf. DT-OS 2 o45 9 ^ and DT-OS 2 o59 539); to reduce the formation of tetrahydrofuran by using less than 2 moles of butanediol (1,4) per mole of dialkyl dicarboxylate and by lowering the pressure in the transesterification reaction.

In the subsequent polycondensation of the transesterification, generally at about 24o - 290 ⁰ C is performed under reduced pressure, formed as a byproduct an oligoester distilled off together with the cleaved butanediol (1,4). After some time, this oligoester clogs the reactor, so that this process step can only be carried out continuously with considerable technical difficulties.

The present invention is based on the knowledge that the transesterification of terephthalic acid or isophthalic acid dialkyl esters with butanediol- (1,4) under increased pressure to a considerable reduction in the formation of tetrahydrofuran leads that the transesterification product thus obtained in the subsequent Polycondensation results in polycondensates with higher molecular weights and that reduces the amount of oligoesters will.

The invention accordingly relates to a process for condensation of diols and dicarboxylic acid dialkyl esters, which is characterized in that one butanediol (1,4) or its mixture with a maximum of 10 mol percent of another diol with dialkyl esters of terephthalic acid and / or isophthalic acid or mixtures of these esters condensed with a maximum of 10 mol percent of other dialkyl dicarboxylates, whereby

a) 1 mol of the dialkyl dicarboxylate with 1.05 to 1.9 mol of the diol in the presence of 0.01 to 0.4 percent by weight of a catalyst, based on the dicarboxylic acid dialkyl

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ester, is continuously transesterified at a pressure of 2 - 10 bar and a temperature of 180 'to 2JO ^{0 C,}

b) the transesterification product at 230-300 ° C at reduced Pressure of 0.1 to 5 Torr is polycondensed in the melt and

c) the polyester thus obtained at a temperature of

5 to 50 ° C below its melting point under reduced pressure or under an inert gas atmosphere will until its intrinsic viscosity is in the range of 0.6 to 1.9 dl / g.

1
Butanediol- (1,4) is used as the starting material for the process. However, up to 10 mol percent thereof can be replaced by other diols. Other diols are preferably aliphatic diols of the formula OH- (CHp) -OH, where η is 2, 3 or 5 to Io, such as e.g. B. hexanediol, ethylene glycol. Cyclohexanedimethanol and neopentyl glycol are also suitable.

Dialkyl esters of terephthalic acid, dialkyl esters of isophthalic acid or any mixtures of these two esters are used as the second starting product. The alkyl groups generally contain 1-6 carbon atoms. Up to 10 mol percent of these esters can be replaced by corresponding other dicarboxylic acids. Particularly suitable are the C ₁ - Cg dialkyl esters of aliphatic dicarboxylic acids of the formula HOOC- (CHg) _n -COOH, where η = 0-8, such as diethyl oxalate, dimethyl succinate, diethyl adipate and diesters of aromatic dicarboxylic acids e.g. B-. of naphthalenedicarboxylic acids, 4,4'-benzophenonedicarboxylic acid and diphenylsulfonedicarboxylic acid. In general, 1.05 to 1.9 mol of diol, preferably 1.1 to 1.5 mol, are used per mole of dicarboxylic acid ester.

Catalysts for the first stage of the process, which are in Amounts of 0.01 to 0.4 percent by weight, based on the diester, are used, in particular, titanic acid tetra-

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alkyl esters, preferably with -1-6 carbon atoms in the Alkyl group such as ζ. · B. Titanium tetraisopropoxide. The first Stage is preferred at an overpressure of 2 - Io bar 3-6 bar. The reaction temperature is l8o 23o ° C, preferably 200-220 ° C.

The intrinsic viscosity is determined by viscosity measurements in tetrachloroethane / phenol in a weight ratio of 1: 1 as solvent and extrapolation to the limit value for the concentration O according to the following equation / PlJ = limit t specific / ~ dl / g_7

C ^ 0 6

Furthermore, before, during and after the polycondensation Stabilizers are added. These stabilizers are preferably organic phosphites and phosphates or steric hindered phenols, e.g. B. Decyl-diphenyl-phosphite, Tr-isnonylphenyl-phosphite, Phenyl neopentyl phosphite, distearyl dipentaerythritol diphosphite and triphenyl phosphate.

5 to 80% reinforcing fillers, based on the total weight of polyester and filler, preferably glass fibers, can be added to the polyesters or copolyesters produced according to the invention.

The polyesters produced according to the invention can also or copolyester contain flame retardant additives.

All known flame retardants, preferably combinations of halogen-containing additives, can be used as flame-retardant additives organic compounds, e.g. B. halogenated benzenes, halogenated diphenyl ethers, halogenated diphenyls and polyphenyls, halogenated polycarbonates (preferably from

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Tetrabromobisphenol A), with organic or inorganic Antimony compounds, ζ. Β. Antimony trioxide, elemental Phosphorus or phosphorus compounds can be used.

The amount of the flame-retardant additive is generally about 2 to J> o percent by weight, based on polyester and filler, preferably 5 and 15 percent by weight.

The polyesters or copolyesters obtained according to the invention can because of their high molecular weight z. B. by injection molding or extrusion to moldings with excellent Long-term use properties are processed.

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example

794 kg of dimethyl terephthalate, 505 kg of butanediol (1,4) (corresponding to a molar ratio of 1.4 mol of butanediol (1.4) to 1 mol of dimethyl terephthalate) and 74o g of titanium tetraisopropoxide (corresponding to 0.093 %> based on dimethyl terephthalate), 15 percent dissolved in butanediol (1.4), are metered in. The transesterification zone is heated to 210 ° C. At a pressure of 3 bar set by a vapor valve, the transesterification is carried out until the transesterification has covered 70 % of the methanol that can be split off, ie until the amount of methanol split off per hour is 183 kg.

The amount of tetrahydrofuran formed hourly is 1.76 kg, corresponding to a loss of 0.4 % butanediol- (1,4).

The transesterification product is then placed in an intermediate container pumped where the pressure is lowered to 15 torr. In a downstream polycondensation reactor is a Temperature of 2βο C and a pressure of 2 Torr the polycondensation continued up to the viscosity maximum. The spun and granulated polybutylene terephthalate has a Intrinsic viscosity of 1.018 dl / g and a melt viscosity (at 28o ° C) of 148O poise.

In the case of post-condensation at 200 ° C. under the conditions mentioned in Example 1, the intrinsic viscosity increases 1.528 dl / g and the melt viscosity (at 280 ° C) to 6800 Poise.

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Claims (1)

Claim Process for the condensation of diols and dicarboxylic acid dialkyl esters, characterized in that "one butanediol (1,4) or its mixture with at most 10 mol percent of another Diol with dialkyl esters of terephthalic acid and / or isophthalic acid or mixtures of these esters condensed with at most 10 mol percent of other dialkyl dicarboxylates, with a) 1 mol of the dialkyl dicarboxylate with 1.05 to 1.9 mol of the diol in the presence of 0.01 to 0.4 percent by weight of a catalyst, based on the dialkyl dicarboxylate, at a pressure of 2-10 bar and a temperature is continuously transesterified from 180 to 230 ° C, b) the transesterification at 230-300 ⁰ C under reduced pressure of 0.1 to 5 Torr in the melt is polycondensed and c) the polyester thus obtained is ^{further condensed at a temperature of 5 to 50 °} C. below its melting point under reduced pressure or under an inert gas atmosphere until its intrinsic viscosity is in the range from 0.6 to 1.9 dl / g. Le A 17 367 - 7 - 609850/0831