DD240309A3 - METHOD FOR PRODUCING HIGH-MOLECULAR POLYALKYLENEPEPTALATES BY SOLID PHASE ABOLIN CONDENSATION - Google Patents

Abstract

The invention relates to a process for the preparation of high molecular weight polyalkylene terephthalates by postcondensation in the solid phase, in particular of polyesters based on polyethylene and polybutylene terephthalate. The aim of the invention is the Festphathennpolykondensation of polyalkylene terephthalates in the presence of oxygen-containing gases such. As air or oxygen contaminated inert gases. According to the invention, this is achieved by the addition of antioxidants which are applied to the surface of the solid polyester particles or introduced into the polyester melt before deformation.

Description

Field of application of the invention

The invention relates to a process for the preparation of high molecular weight polyalkylene terephthalates ₍ especially polyethylene and polybutylene terephthalate by post-polycondensation in the solid phase, which are particularly well suited as a construction material, such as for use in electrical engineering, automotive and mechanical engineering, or in the fiber and cord industry can be used.

Characteristic of the known technical solutions

Numerous processes are already known in which the increase in the average degree of polycondensation of polyesters is achieved by solid polyphase post-polycondensation following conventional melt polycondensation. For example, DD 9346 describes a process for the preparation of synthetic linear polyesters, in particular polyethylene terephthalate, in which the polycondensation is carried out wholly or partly in the solid phase at temperatures below the melting point of the polyester in an inert gas stream.

Special embodiments are i.a. in DD-PS 75639, 91 347, 91 899.93247, 94895, GB-PS 1 066162, US-PS 2901466, 3075952 and DE-OS 1 720623 described in which a transferred into the solid phase, powdered or Granulated polycondensate is heated for several hours in an inert gas stream or in vacuo at temperatures below the melting point, and thereby transferred with elimination of glycol and water in a product with a higher average degree of polycondensation.

In all previously known methods for solid-phase post-polycondensation of polyalkylene terephthalates, there is a need to carefully exclude traces of oxygen during the reaction to prevent the thermo-oxidative degradation, otherwise prevented by oxidative degradation reactions of the intended effect and even a decrease in the molecular weight is caused.

Object of the invention

The object of the invention is to improve the solid state post-polycondensation of polyalkylene terephthalates in the presence of oxygen-containing gases, e.g. To carry out air or oxygen-contaminated inert gases, thereby reducing the cost and cost of cleaning the carrier gases used.

Explanation of the essence of the invention

- Task

The object of the invention is to exclude by suitable additives the post-polycondensation preventing influence of the oxygen in the carrier gases used, as well as to prevent a post-polycondensation superimposed thermo-oxidative degradation.

Features of the invention

Surprisingly, it was found that the Festphasennachpolykondensation of polyalkylene terephthalates contrary to the previously expressed view (DD-PS 91 347) can be carried out in the presence of oxygen-containing gases, if the polyesters before the Festphasennachpolykondensation suitable under the reaction conditions low volatility antioxidants based on secondary arylamines, Ketone-amine condensates or phenol derivatives, e.g. As di-naphthyp-phenylenediamine, cyclohexanone-diphenylamine condensate (CDK), Dodecylgallat be added.

The antioxidants are applied directly before the post-polycondensation on the surface of the polyester granules or powder or introduced into the melt of the polyester prior to their deformation into granules or chips.

In the absence of the antioxidants, a more or less rapid decrease in the average degree of polycondensation and an increase in the carboxyl group content can be observed in solid phase post-polycondensation in the presence of oxygen-containing gases. In the postpolycondensation of antioxidant polyalkylene terephthalates according to the invention takes place

in contrast, in the presence of oxygen-containing gases, eg. B. in a dry air stream, which can also serve to move the granules, a rapid increase in the average degree of polycondensation. Polyalkylene terephthalates in the context of the invention are polyesters, preferably based on polyethylene or polybutylene terephthalate, which in addition to the main components terephthalic acid and ethylene glycol or 1,4-butanediol or other di- or polycarboxylic acids and / or dihydric and / or polyhydric alcohols which also contain molecular weights may contain up to 20,000 daltons. The polyalkylene terephthalates of the invention may further contain finishing agents, pigments and other additives.

embodiments

1st comparative example

250 g of granules of polyethylene terephthalate (PET) of average grain size 2 χ 3 χ 4mm with a mean Polymondensationsgrad P _n = 110 and a carboxyl group content of 33μ equ / g are in an obliquely immersed in a salt bath rotating flask in a stream of dried nitrogen (25 l / h) dried as a carrier gas at a bath temperature of 170 ^c C for 1 hour and then subjected to a bath temperature of 245 ⁰ C of a solid phase post-polycondensation. After 5 hours, P _n = 172 and the carboxyl group content is 22.0 μ eq / g.

2nd Comparative Example

250 g of PET are subjected to post-polycondensation ₍ as in Example 1) in a stream of dry air (25 l / h) After 5 hours the P _n = 90 and the carboxyl group content 85 μ eq / g.

3. 250 g of a PET granulate. As in Example 1 and 2, are thoroughly mixed with 0.25 g of CDK at room temperature and subjected as in Example 2 to a Festphasennachpolykondensation under air. After 5 hours, the P _n = 170 and the carboxyl group content 25 μ Eq / g.

4. 250 g of a PET granulate are subjected to solid phase post-polycondensation as in Example е.еіпег, using dry nitrogen with a residual oxygen content of 1% as the carrier gas. After 5 hours the P _n = 172.

5. 250 g of a PET granulate are polycondensed, as in Examples 3 and 4, in a СОг stream with an oxygen content of 4%. After 5 hours, the P _n = 170.

6. 250 g of a PET granulate, as in Examples 1 and 2, are mixed with 0.05 g of dinaphthyl-p-phenylenediamine and subjected to a Festphasennachpolykondensation under air as in Example 2. After 5 hours, a P _n = 160 is reached, the carboxyl group content is 23.8 μ eq / g.

7. 250 g of a PET granulate, as in Examples 1 and 2, are mixed with 1 g of dodecyl gallate and, as in Example 2, subjected to solid-phase post-polycondensation under air. After 3 hours, a P _n = 140 was reached.

8. 250 g of polybutylene terephthalate granules having an average grain size of 2 χ 3 χ 3mm and an average degree of polymerization of P _n = 126, containing 0.5 wt .-% antioxidant CDK, are in a salt bath in a rotating flask at a bath temperature of 215 ° C with a stream of dry air (25 l / h) subjected to a Nachpolykondensation. The average degree of polymerization P _{n of} the granules is 183 after 6 hours treatment time and 257 after 12 hours treatment time.

Claims (4)

Invention claim: 1. A process for the preparation of high molecular weight polyalkylene terephthalates by Festphasennachpolykondensation, characterized in that the post-condensation in an oxygen-containing gas stream with the addition of 0.01-1.0 Ma .-% antioxidants based on secondary arylamines, ketone-amine condensates or phenol derivatives he follows. 2. The method according to item 1 to 3, characterized gekenn2eichnet that are used as antioxidants CDK, dinaphthyl-p-phenylenediamine or Dodecylgallat. 3. The method according to item 1, characterized in that the oxygen-containing gas is air. 4. The method according to item 1, characterized in that oxygen is contained in other gases, in particular carbon dioxide and nitrogen.