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 having good thermal stability and a weight average molecular weight of >100,000 by GPC. The process includes mixing glycolic acid and/or lactic acid, and a diol or di-acid initiator, and at least one multifunctional initiator to form a liquid monomer mixture in an agitated polycondensation reactor. Polycondensing 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% by mole hydroxyl or carboxyl end-group termination, then crystallizing to form a first solid reaction mixture. Then solid state polycondensing the solid reaction mixture to form a solid reaction mixture having a moisture level less than 50 ppm by weight. Then mixing the solid reaction mixture with an appropriate reactive coupling agent in a melting and mixing extruder to couple and form the reaction mixture and form the poly(hydroxy acid) polymer.
1. A process for making a (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 di-functional acid initiator, and a multi-functional acid 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 % carboxyl 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 % carboxyl end-group termination,
mixing the second solid reaction mixture with at least one of a di-functional bis-oxazoline 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.
2. The process of claim 1 , wherein the liquid monomer mixture remains in the agitated polycondensation reactor during the polycondensing, the liquid reaction mixture remains in the agitated polycondensation reaction during crystallizing, and the second solid reaction mixture remains in the agitated polycondensation reaction during the solid state polycondensing such that the pre-polymer, the first solid reaction mixture and the intermediate-polymer are not removed from the agitated polycondensation reactor prior to forming the coupling reaction mixture.
3. The process of claim 1 , wherein the liquid reaction mixture is agitated in the agitated polycondensation reaction during the crystallizing to form particles of the solid reaction mixture.
4. The process of claim 3 , wherein the average particle size of the particles of the solid reaction mixture is less than 3 mm.
5. The process of claim 4 , wherein the crystallizing includes cooling the liquid reaction mixture to a temperature of no greater than 180° C.
6. The process of claim 1 , wherein the liquid monomer mixture is polycondensed at a temperature of ≥190° C. to 220° C.
7. The process of claim 1 , wherein the solid reaction mixture is solid state polycondensed at a temperature of from 140° C. to ≤180° C.
8. The process of claim 1 , wherein the coupling reaction mixture is formed and coupled in the melting and mixing extruder.
9. The process of claim 1 , wherein the liquid monomer mixture is polycondensed at a temperature of 190-220° C. and the solid reaction mixture is solid state polycondensed at a temperature of 150-180° C.
10. The process of claim 1 , wherein the crystallizing includes cooling the liquid reaction mixture in the agitated polycondensation reactor at a rate of 10° C./min or greater.
11. The process of claim 1 , wherein the temperature remains above 150° C. during the crystallizing and the solid state polycondensing.
12. The process of claim 1 , wherein the pressure in the agitated polycondensation reactor remains below 500 mbar during the polycondensing and the crystallizing.
13. 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.
14. The process of claim 13 , wherein the liquid monomer mixture remains in the agitated polycondensation reactor during the polycondensing, the liquid reaction mixture remains in the agitated polycondensation reaction during crystallizing, and the second solid reaction mixture remains in the agitated polycondensation reaction during the solid state polycondensing such that the pre-polymer, the first solid reaction mixture and the intermediate-polymer are not removed from the agitated polycondensation reactor prior to forming the coupling reaction mixture.
15. The process of claim 13 , wherein the liquid reaction mixture is agitated in the agitated polycondensation reaction during the crystallizing to form particles of the solid reaction mixture.
16. The process of claim 15 , wherein the average particle size of the particles of the solid reaction mixture is less than 3 mm.
17. The process of claim 16 , wherein the crystallizing includes cooling the liquid reaction mixture to a temperature of no greater than 180° C.
18. The process of claim 13 , wherein the liquid monomer mixture is polycondensed at a temperature of ≥190° C. to 220° C.
19. The process of claim 13 , wherein the solid reaction mixture is solid state polycondensed at a temperature of from 140° C. to ≤180° C.
20. The process of claim 19 , wherein the coupling reaction mixture is formed and coupled in the melting and mixing extruder.