DD241826A3 - METHOD FOR PRODUCING POLYBUTYLENEPEPHTHALATE - Google Patents

Abstract

The invention relates to a process for the preparation of high molecular weight polyethylene terephthalate based on terephthalic acid and butanediol. By setting certain initial parameters, it is possible to accelerate the esterification of terephthalic acid and to carry out the polycondensation with a carboxyl group-free esterification. As a result, higher molecular weights of the final product are achieved.

Description

Field of application of the invention

The invention relates to a method for the gentle production of polybutylene terephthalate (PBTP) of high average molecular weight by esterification of terephthalic acid with butanediol, which can be used as a starting material for the production of moldings, films or fibers.

Characteristic of the known technical solutions

Polyesters, such as polybutylene terephthalate, can be prepared by transesterification of dialkyl terephthalates with alkanediols or else by esterification of terephthalic acid with alkanediols. For the synthesis of PBTP, the transesterification of dimethyl terephthalate with butanediol with subsequent polycondensation of the bis (4-hydroxibutyl) terephthalate formed is predominantly used. The esterification of terephthalic acid with butanediol is due to the rather high butanediol losses by tetrahydrofuran formation economically disadvantaged compared to the transesterification process. To reduce Butandiolverluste various methods and methods are described. In the majority of cases, an attempt is made to increase the reaction rate during esterification by increasing the catalyst activity. The higher reaction rate is said to rapidly decrease the concentration of free terephthalic acid to rapidly decrease the acidity of the reaction system and thereby minimize the acid catalyzed dehydration of the butanediol. Frequently described catalysts are titanic acid esters (cf., for example, DE-OS 2210655, JP-A 7439694, JP-A 7582196) or organotin compounds (cf., for example, DE-OS 2621099). The catalysts used correspond to those of the transesterification processes.

Furthermore, an attempt is made to reduce the system acidity or the contact time between terephthalic acid and butanediol by adding dimethyl terephthalate (DE-OS 2332566, DE-OS 2407156) by using particularly fine-grained terephthalic acid (DE-OS 2210655) or by portionwise addition of terephthalic acid ( DE-OS 2407155). The aforementioned purely technological process variants, however, burden a large-scale production of PBTP from terephthalic acid in unnecessary. Thus, the use of a mixture of terephthalic acid and dimethyl terephthalate would considerably complicate the workup of the vapors by the separation of methanol, water, tetrahydrofuran and butanediol and require a lot of equipment. A gradual supply of terephthalic acid is feasible only in continuous processes. Such a method is thus considerably limited in its variability and flexibility. The Butandiolverluste by formation of tetrahydrofuran are only one side of this undesirable side reaction. These butanediol losses can be the cause of incomplete conversion of the carboxyl groups. If such an incompletely reacted esterification product is fed to the polycondensation stage, the polycondensation rate is reduced in the case of PBTP and the molar mass of the final product does not reach the required values. However, substantial mechanical properties of the PBTP, for example notched impact strength, are directly proportional to the molar mass, so that the molar mass also influences the quality of the final product.

Object of the invention

The aim of the invention is the development of a process for the preparation of PBTP based on terephthalic acid and butanediol, which leads with high polycondensation rate to a high molecular weight polymer.

Explanation of the essence of the invention

- Task

The invention has for its object to provide such reaction conditions in the esterification and Vorpolykondensationsstufe with which it is possible to produce compared to known technical solutions of higher molecular weight product, and in which the Butandiolverluste by tetrahydrofuran formation are economically justifiable.

Features of the invention

According to the invention the object is achieved in that the polycondensation is fed to a carboxyl group-free esterification.

This results in a reaction rate of esterification and pre-polycondensation, in which the speed

unavoidable side reactions, such as thermal Esterendgruppenspaltung or dehydration, is negligible.

It has been found that the carboxyl ester-free esterification mixture is obtained when the monomer ratio of butanediol to terephthalic acid in the range of 3: 1 to 10: 1, preferably 4: 1. The process according to the invention not only increases the esterification and prepolycondensation rate, but also achieves a faster increase in the degree of polymerization in the polycondensation phase.

Tables 1 and 2 show the effects of various carboxyl group concentrations, the consequence of different monomer ratios, on the P _n increase and the achievable P _n .

The butanediol losses by tetrahydrofuran are only slightly dependent on the molar ratio of the monomers, since the higher butanediol content in the process according to the invention greatly increases the rate of esterification and the dehydrating activity of the free carboxyl groups can only be effective for a short time (Table 3).

As catalysts, the titanium alkoxides commonly used for the preparation of PBTP can be used, in addition to the Orthotitansäureestern also oligotitanates are suitable.

Copolymers of the PBTP with further bifunctional or higher-functional alcohols or dicarboxylic acids can advantageously also be prepared by the process according to the invention. Thus, in addition to butanediol, ethylene glycol (10-90 mol%), glycerol (1-10 mol%) or pentaerythritol (0.5-5 mol%) can be used as second hydroxyl-containing component.

Suitable second dicarboxylic acids are, for example, isophthalic acid (10-50 mol%), 1,4-cyclohexanedicarboxylic acid (10-50 mol%), adipic acid or sebacic acid (in each case 2-10 mol%).

Table 1: Polymerisationsgradzunahme in PBTP melts as a function of reaction time and molar ratio of the monomers, ⁰ t = 250 C, catalyst: 3 x lO ^ mol / mol Ti (OC ₄ Hg) ₄

Monomer ratio of butanediol: TPA / COOH / μΑςυ / g τ / min / pn 1.4: 1 40 60 120 180 74 94 106 2: 1 15 60 120 180 88 120 • 148 3: 1 5 60 120 180 98 130 152 4: 1 5 60 120 180 99 148 190

Table 2: Degree of polymerization in PBTP melts as a function of reaction time and molar ratio of the monomers, t = 250 ° C, catalyst: 3 10 " ⁴ mol / mol dibutyl oligo-titanate

Monomer ratio of butanediol: TPA τ / min / P _n 1.4: 1 60 120 180 74 94 110 1.7: 1 60 120 180 87 105 112 2: 1 60 120 180 98 127 136 3: 1 60 120 180 98 127 160 4: 1 60 120 180 99,144,186

Table 3: Butanediol losses by tetrahydrofuran formation

molar ratio THF share Butandiolverlust % when using 100 g 1.4: 1 10.0 6.3 1.7: 1 10.3 7.9 2: 1 12.6 7.6 3: 1 10.7 9.6 4: 1 9.1 11.4

embodiments

example 1

42,5g terephthalic acid are esterified with 90 ml of butanediol with the addition of 3 x 10 ^"4 mol / mol of Ti (OC ₄ Hg) ₄ within 90 min at 210 ⁰ C. This mixture of oligomeric bis (4-hydroxibutyl) terephthalates is in the Vacuum polycondensed at 0.1-0.3 Torr After 3 h at 250 ⁰ C, a degree of polymerization of P _n = 190 is reached.

Example 2 '

2650g terephthalic acid are esterified with 5700ml butanediol with the addition of 3 10 ~ ⁴ mol / mol dibutyl oligo-titanate in a laboratory reactor with anchor agitator within 150min at 200 ° C-210 ° C. This mixture of oligomeric bis (4-hydroxibutyO terephthalates, first at 20 Torr for 30 min and then polycondensed at 0.5 torr for 90 min at 250 ⁰ C. The resulting polymer has a degree of polymerization of P _n = 175.

Claims (2)

Invention claim: 1. A process for the preparation of high molecular weight polybutylene terephthalate by esterification of terephthalic acid and butanediol and subsequent polycondensation, characterized in that the polycondensation is fed to a carboxylgruppenfreiesVorpolykondensat. 2. A process according to item 1, characterized in that the carboxyl group-free prepolycondensate is achieved at a monomer ratio of butanediol terephthalic acid in the range 3: 1 to 10: 1.