Process for making poly(ethylene-co-isosorbide) terephthalate polymer

A melt polymerization process for the preparation of poly(ethylene-co-isosorbide)terephthalate (PEIT), comprising:

• a) providing a mixture comprising terephthalic acid or its alkyl ester, ethylene glycol and isosorbide, wherein the molar ratio of diols to terephthalic acid or its alkyl ester is from about 1.05:1 to about 1.3:1 and the molar ratio of ethylene glycol to isosorbide is from about 1.2:1 to about 24:1;
• b) reacting the mixture in an inert atmosphere at a temperature in the range 180-255° C. and a pressure in the range of 0-60 psig, with concurrent removal of a distillate comprising water or volatile alkanol products derived from the reaction of terephthalic acid or its ester with ethylene glycol and isosorbide, wherein the distillate contains less than about 5 wt % ethylene glycol and less than about 1 wt % isosorbide;
• and
• c) continuing the reaction in the presence of a polycondensation catalyst at a pressure of about 0.25 to about 2 mm and a temperature of 260 to 275° C. to form a PEIT having a Hunter b* color value between about −2.0 and about +2.0.