Process for making poly(glycolic acid) for containers and films with reduced gas permeability

A process for making a high molecular weight (poly)hydroxy acid polymer comprising at least 90% by weight of reacted units of one or more hydroxy acid monomers and having a weight average molecular weight of >100,000 by GPC, the process comprising:

• mixing one or more hydroxy acid monomers selected from the group consisting of glycolic acid and lactic acid, a diol initiator, and a multi-functional initiator to form a liquid monomer mixture in an agitated polycondensation reactor,
• polycondensing the liquid monomer mixture to form a liquid reaction mixture comprising a pre-polymer having a weight average molecular weight of >10,000 by GPC, and greater than 80 mol % hydroxyl end-group termination,
• crystallizing the liquid reaction mixture in the agitated polycondensation reactor to form a first solid reaction mixture,
• solid state polycondensing the solid reaction mixture to form a second solid reaction mixture having a moisture level less than 50 ppm by weight and comprising an intermediate-polymer having weight average molecular weight of >20,000 by GPC, and greater than 90 mol % hydroxyl end-group termination,
• mixing the second solid reaction mixture with at least one of a di-functional di-isocyanate reactive coupling agent and a multi-functional reactive coupling agent to form a coupling reaction mixture, and
• reacting the coupling reaction mixture in a melting and mixing extruder to form the poly(hydroxy acid) polymer.