Process for reducing the processing time in the production of polyesters

Abstract

Polyesters obtained by reacting isophthalic acid or terephthalic acid with a polyol with or without a catalyst in a first stage to form a half-ester mixture which is reacted in a second stage with an aliphatic polycarboxylic acid are produced at reduced processing times. In the first stage a portion of the total polyol to be reacted is contacted with substantially all of the isophthalic acid or terephthalic acid. Then, this mixture is heated with agitation to a temperature of at least 190° C. and the remaining portion of the polyol is added to the heated mixture with agitation in such a manner that the temperature remains at or above the 190° C. This temperature is maintained until the reaction to form a half-ester mixture is completed. This reaction may be conducted in the presence of an esterification catalyst. The polyester-monomer mixture is reacted in a second stage with an aliphatic polycarboxylic acid to produce the polyester.

I claim: 
     
       1. In a two-stage process for the production of polyesters wherein an aromatic polycarboxylic acid selected from the group consisting of isophthalic acid and terephthalic acid is reacted in the first stage with a polyol to produce half-ester mixture which is reacted with a saturated or unsaturated aliphatic polycarboxylic in the second stage to produce the polyester, to reduce the processing time in the first stage; thereby reducing the processing time for the production of the polyester, comprising: a. contacting first portion of the polyol with the aromatic polycarboxylic acid in the first stage in an amount at least sufficient to form an agitatable mixture with the aromatic polycarboxylic acid but in an amount slightly less than the theoretical amount of polyol needed to react with the isophthalic acid or terephthalic acid and saturated or unsaturated aliphatic polycarboxylic acid,   b. heating the agitatable mixture .Iadd.with agitation .Iaddend.to a temperature of at least 190° C. to 230° C., and   c. adding the remaining portion of the polyol to the heated agitatable mixture .Iadd.with agitation .Iaddend.in the first stage in such a manner that the temperature of the heated agitatable mixture is maintained at a temperature of at least 190° C. in order to produce a half-ester mixture.   
     
     
       2. A process according to claim 1 wherein an esterification catalyst selected from the group consisting of inorganic salts and organic compounds of tin, lead or lithium and mixtures of said salts and compounds, and tetrabutyl zirconate, and zirconium naphthenate is used in the first stage during contacting of the first portion of polyol and aromatic polycarboxylic acid and heating of the agitatable mixture and adding the remaining portion of polyol to the heated agitatable mixture. 
     
     
       3. A process according to claim 2 wherein the catalyst is dibutyl tin oxide present in an amount of 0.01 to 2.0 percent by weight of the total weight of the charge in the first stage. 
     
     
       4. A process according to claim 1 wherein the unsaturated polycarboxylic acid is selected from the group of acids and anhydrides consisting of maleic acid or anhydride, fumaric acid or anhydride, itaconic acid or anhydride, citraconic acid or anhydride, glutaconic acid or anhydride, and mesaconic acid or anhydride. 
     
     
       5. A process according to claim 1 wherein the polyol is selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, neopentyl glycol, trimethylene glycol, polyethylene glycol and polypropylene glycol. 
     
     
       6. A process according to claim 1 wherein the amount of polyol present in the first portion of polyol is in the range of 0.5 to 1.7 moles of polyol per mole of aromatic polycarboxylic acid. 
     
     
       7. A process according to claim 1 wherein the remaining portion of polyol is heated to a temperature in the range from ambient temperature to a temperature less than the boiling point of the polyol before the remaining portion is added to the heated agitatable mixture in order to add the remaining portion of polyol while maintaining the temperature of the heated agitatable mixture at a temperature of at least 190° C. 
     
     
       8. A process according to claim 1 wherein the first portion of polyol is contacted with a first portion of the aromatic polycarboxylic acid present in a substantial amount and the remaining portion of the aromatic polycarboxylic acid is added after the mixture of the first portions of polyol and aromatic polycarboxylic acid is heated. l 
     
     
       9. A process according to claim 1 wherein the amount of polyol present in the first portion of polyol is in the range of 0.8 to 1.4 moles of polyol per mole of aromatic polycarboxylic acid.