Process for preparing polyesters by using an additive

Abstract

A process for reducing the amount of hydroxyl-end-groups of a polyester, wherein the polyester is prepared from at least one dicarboxylic acid and at least one dihydroxy alcohol, and at least one additive selected from the group consisting of carboxylic acid anhydride and mono-isocyanate, and wherein the additive is added during a step of prepolycondensation and/or during a step of polycondensation and/or after a step of polycondensation.

Claims

1. A process for reducing the amount of hydroxyl-end-groups of a polyester, wherein the polyester is prepared from at least one dicarboxylic acid and at least one dihydroxy alcohol, and at least one additive selected from the group consisting of carboxylic acid anhydride and mono-isocyanate.

2. The process according to claim 1, wherein the additive is added during a step of prepolycondensation and/or during a step of polycondensation and/or after a step of polycondensation.

3. The process according to claim 1, wherein the carboxylic acid anhydride used as additive has the same or a different basic hydrocarbon structure compared to the dicarboxylic acid used as monomer.

4. The process according to claim 1, wherein the carboxylic acid anhydride is selected from the group consisting of glutaric acid anhydride, acetic acid anhydride and succinic acid anhydride.

5. The process according to claim 1, wherein the mono-isocyanate is phenyl-isocyanate.

6. The process according to claim 1, wherein the additive is added in an amount of 0.1 to 10% in relation to the final polyester.

7. The process according to claim 1, wherein the additive is added in an amount of 0.2 to 1.0% in relation to the final polyester.

8. The process according to claim 1, wherein the polyester comprises dicarboxylic acid compounds and diol compounds; and wherein the dicarboxylic acid compounds are a) linear dimeric acids having a molecular formula C.sub.nH.sub.2(n-1)O.sub.4 with n equal to or smaller than 40, and/or b) dimeric acids or dicarboxylic acids having a cyclic ring, and/or c) esters of the dicarboxylic acids or acid anhydrides of the dicarboxylic acids; wherein the dicarboxylic acid compounds comprise a single compound or as mixture of two or more compounds; and wherein the diol compounds are aliphatic or alicyclic compounds having two —OH groups.

9. The process according to claim 8, wherein the esters of the dicarboxylic acids are selected from the group consisting of methyl ester, ethyl ester, propyl ester and butyl ester.

10. The process according to claim 1 wherein the polyester comprises dicarboxylic acid compounds as well as their respective ester wherein the dicarboxylic acid compounds comprise a single compound or as a mixture of two or more compounds; and diol compounds with 2-10 carbon atoms wherein the diol compounds comprise a single compound or as a mixture of two or more compounds.

11. The process according to claim 10, wherein the respective ester is selected from the group consisting of methyl ester, ethyl ester, propyl ester and butyl ester.

12. The process according to claim 8 wherein the linear dimeric acids having a molecular formula C.sub.nH.sub.2(n-1)O.sub.4 with n equal to or smaller than 40 are selected from the group consisting of oxalic-, malonic-, succinic-, glutaric-, adipinic-, and pimelic-acid.

13. The process according to claim 8 wherein the dicarboxylic acid having a cyclic ring is cyclohexane dicarboxylic acid.

14. The process according to claim 10 wherein the dicarboxylic acid compounds are selected from the group consisting of terephthalic acid, isophthalic acid, 2,6-naphtalenedicarboxylic acid and acids having a furan ring.

15. The process according to claim 14 wherein acid having a furan ring is furan dicarboxylic acid.

16. The process according to claim 10 wherein the diol compounds with 2-10 carbon atoms are selected from the group consisting of ethyleneglycol, 1,3-proanediol, 1,4-butanediol, neopentylglycol, 1,6-hexamethyleneglycol, 1,4-cyclohexanedimethanol, polyglycols based on ethylene glycol or trimethyleneglycol, 1,4-butaneidol, and polytetrahydrofurane (polytetramethylene ether glycols).

Description

EXAMPLE 1 AND COMPARATIVE EXAMPLE 1

(1) A 10 l autoclave was used for the reaction steps from the beginning to the end.

(2) The following Example 1 was carried out.

(3) Esterification:

(4) Recipe:

(5) 1385.1 terephthalic acid (PTA)

(6) 1089.4 g butanediol (BDO, molar ratio 1:1.45)

(7) 1460 g Hombifast HS-06 (60 ppm Ti related to final polymer)

(8) 47.4 g polyethylene glycol 400 (PEG 400, 13 kg/to)

(9) 2.55 g pentaerythritol (0.7 kg/to)

(10) Esterification of PTA

(11) The monomers and the catalyst were put into the reactor and stirred continuously. After rendering inert, the reactor was heated. When the product temperature reached 195° C. (start of time measurement), the pressure was reduced within 15 minutes to 400 mbar while the product temperature increased further to 240° C. Esterification was finished after 120 minutes.

(12) Preparation of Adipic Acid Solution in BDO

(13) Recipe:

(14) 1319.5 g adipic acid (ADA)

(15) 789.3 g BDO (molar ratio 1.00)

(16) BDO was filled into a vessel and afterwards adipic acid was added. The vessel was rendered inert by nitrogen. The mixture was heated up to 160° C. under slight overpressure and stirred until the PTA esterification was finished. During this time, the adipic acid dissolved in BDO.

(17) Continuation of Esterification:

(18) The adipic acid-BDO-solution was fed into the esterification reactor within approximately 5 minutes. The product temperature, as a result of the feed and the set down of the heating temperature, dropped to 190° C. and increased in the ongoing esterification to 212° C. The condensate yield indicated the target end of the esterification reaction after a total of 160 minutes after start of time measurement.

(19) Prepolycondensation:

(20) The condensing system was switched from esterification condenser to prepolycondensation cooling traps and the pressure was reduced to 150 mbar within 5 minutes and further to 35 mbar within 5 minutes. This target pressure was kept constant for 10 minutes. The melt temperature averaged at 235° C. The overall prepolycondensation time was 20 minutes.

(21) Addition of Polycondensation Catalyst:

(22) An amount of 2.07 g Tyzor TnBT catalyst (Dorf Ketal, 80 ppm Ti related to the final polymer) was fed afterwards and -flashed down with 10 g BDO in the reactor.

(23) Polycondensation:

(24) The condensing system was switched from prepolycondensation cooling traps to polycondensation cooling traps. The pressure was reduced within 15 minutes to <1 mbar. The temperature during the polycondensation was 240° C.

(25) After a polycondensation time of 190 minutes 20 g succinic acid anhydride was fed to the polycondensation reaction, which is an amount of 0.55% in relation to the final polymer.

(26) The polycondensation time was 340 minutes. After breaking the vacuum by nitrogen, the polymer was discharged by pressure and granulated, the intrinsic viscosity of the final polymer product was 1.6 dl/g.

(27) The Comparative Example 1 differs from Example 1 in that no succinic acid is added. More details of Example 1 in particular in comparison with Comparative Example 1 are shown in the following table 1:

(28) Briefly, first an esterification reaction was done with terephthalic acid, then adipic acid was fed together with BDO and it was fed preheated to this preproduct for further reactions. Different molar ratios of butanediol to acid were chosen.

(29) TABLE-US-00001 TABLE 1 Comparative Example Example 1 Molar ratio start of 1:1.00 1:1   esterification BDO:ADA Molar ratio start of 1:1.40 1:1.45 esterification BDO:PTA ADA [mol-%] 52 52 PTA [mol-%] 48 48 Pentaerythritol 0.7 kg/t 0.7 kg/t Polyethyleneglycol 13 kg/t 13 kg/t 400 Catalyst140 ppm Ti 140 ppm Ti Feed of succinic acid — 0.55% anhydride 190 minutes after start of polycondensation Polycondensation time 340 [min]330 Final product IV 1.6 dl/g 1.6 dl/g Final product COOH 11 meq/kg 38 meq/kg THF in pellets 28 16 product [ppm] L (Chips, cryst.) (Cielab) 67.6 76.4 A (Chips, cryst.) (Cielab) 29.8 6.8 B (Chips, cryst.) (Cielab) 44.4 17.7

(30) The THF value of the Example 1 was lower than that of Comparative Example 1 indicating a higher thermal degradation.

(31) By adding succinic acid anhydride to the polycondensation a reduction of the OH-end-groups in relation to the —COOH-end-groups has been achieved resulting in a modification of the overall polymer structure. Color values were improved after feeding succinic acid anhydride to the polymer during polycondensation. This may indicate a reduction in color forming side-reactions by adding the additive.

EXAMPLE 2

(32) PBT was mixed with three different additives and then melted and reacted at 250-251° C. for a residence time of 3-3.2 minutes and pelletized.

(33) In the following table 2 the results are shown. It is shown that the OH-end-groups were reduced in comparison to PBT without these additives.

(34) TABLE-US-00002 TABLE 2 Analyzed Analyzed - COOH- Difference OH-end- end- between groups in group in OH-end- polymer polymer groups and —COOH- Amount of product product end- No Additive Additive [meq/kg] [meq/kg] groups 1 No 0 70 24 46 additive 2 Glutaric   4 g/kg 45 41 4 acid anhydride 3 Acetic 3.6 g/kg 57 30 27 acid anhydride 4 Phenylisocyanate 4.2 g/kg 44 24 20