Process for manufacturing medium and high molecular weight polyesters

摘要

Medium and high molecular weight polyester polymers are prepared in syrup form from an ester oligomer. The oligomer is converted to the polymer by polycondensation at elevated pressure and elevated temperature in a nonreactive carrier capable of forming an azeotrope with water. The ester oligomerization or polycondensation reactions desirably are monitored using a non-viscometric technique. The process has a rapid cycle time. The syrup contains the polymer and nonreactive carrier, and may more conveniently be used to make initially non-solid products such as polyester coatings than is the case when employing pelletized solid polyester resins.

主权项

1. A process for preparing high molecular weight polyester syrups, which process comprises:
a) providing or forming an ester oligomer in a first esterification step and substantially without ethylene glycol or propylene glycol, wherein the hydroxyl:acid or hydroxyl:ester ratio is from about 0.98:1 to about 1.1:1; b) converting the oligomer to a polyester polymer by stirring at pressure of about 34 kPa to about 100 kPa gauge and elevated temperature a reaction mixture containing the oligomer and 5 wt.% or more of a nonreactive carrier capable of forming an azeotrope with water and having a boiling point greater than that of xylenes; c) allowing the pressure to rise to about 100 kPa; and d) removing water from the reaction mixture via azeotropic reflux to provide a syrup comprising a medium high molecular weight polyester polymer in the nonreactive carrier.