Process for manufacture of high molecular weight polyester resins from 2,6-naphthalene dicarboxylic acid

A process of preparing a high quality linear polyester resin which comprises:

• (A) reacting in a first step or zone 2,6-naphthalene dicarboxylic acid with a molten hydroxyl-ended prepolymer derived from a glycol and 2,6-naphthalene dicarboxylic acid at temperatures in a range of from about 190.degree. C. to about 320.degree. C. to form a resulting carboxyl-ended prepolymer;
• (B) reacting the carboxyl-ended prepolymer with a glycol in at least two successive steps or zones at temperatures in a range of from about 180.degree. C. to about 330.degree. C. to form a hydroxyl-ended prepolymer;
• (C) partitioning the resulting hydroxyl-ended prepolymer into a condensation fraction and at least one recycle fraction of the hydroxyl-ended prepolymer;
• (D) returning one of the recycle fractions of hydroxyl-ended prepolymer to the first step or zone;
• and
• (E) polymerizing in a polycondensation step or zone at least a portion of the condensation fraction of hydroxyl-ended prepolymer to form polyester resin which exhibits midpoint glass transition temperatures above about 123.degree. C.

A process of preparing a high quality linear polyester resin which comprises;

• (A) reacting in a first step or zone about 10 parts by weight of 2,6-naphthalene dicarboxylic acid with from about 1 part to about 100 parts by weight of a molten hydroxyl-ended prepolymer derived from 2,6-naphthalene dicarboxylic acid and a glycol to form a resulting product comprising acid modified prepolymer;
• (B) reacting in at least two successive steps or zones the acid modified prepolymer of the first step or zone with the glycol to form a product comprising hydroxyl-ended prepolymer;
• (C) partitioning the resulting prepolymer into a condensation fraction and a recycle fraction of the hydroxyl-ended prepolymer;
• (D) returning the recycle fraction to the first step or zone;
• and
• (E) polymerizing in a polycondensation step or zone the condensation fraction of hydroxyl-ended prepolymer to form polyester resin which exhibits midpoint glass transition temperatures above about 124.degree. C.