title: Autocatalytic equation describing the change in molecular weight during hydrolytic degradation of aliphatic polyesters.
abstract: The autocatalytic equation derived in this study describes and even predicts the evolution of the number average molecular weight of aliphatic polyesters upon hydrolytic degradation. The main reaction in the degradation of aliphatic polyesters is autocatalytic hydrolysis of ester bonds, which causes the molecular weight to decrease. During hydrolysis of the ester bonds in the main chain of the polyester, the chains are cleaved and the end group concentrations will rise. The fundamentals of this equation are based on that principle. To validate the derived equation, the hydrolytic degradation of poly(4-methylcaprolactone), poly(epsilon-caprolactone), poly(d,l-lactide), and two different poly(d,l-lactide-co-glycolide) copolymers was monitored after immersion in a PBS buffer (pH = 7.4) at 37 degrees C. The number average molecular weight, mass loss, and crystallinity were determined after different time intervals. The experimental results confirm that hydrolytic degradation of aliphatic polyesters is a bulk erosion process. When comparing the M(n), calculated with the new autocatalytic equation, with the experimental results, it was found that the new model can predict the decrease of the M(n) upon hydrolytic degradation for semicrystalline and amorphous polymers, as well as for copolymers, without the need for complicated mathematics and excessive input parameters. This is a major improvement with respect to earlier proposed models in literature.
authors.affiliation: Product Development Department, N.V. Organon, P.O. Box 20, 5340 BH Oss, The Netherlands.
authors.forename: Harro
authors.initials: H
authors.lastname: Antheunis
authors.forename: Jan-Cees
authors.initials: JC
authors.lastname: van der Meer
authors.forename: Matthijs
authors.initials: M
authors.lastname: de Geus
authors.forename: Andreas
authors.initials: A
authors.lastname: Heise
authors.forename: Cor E
authors.initials: CE
authors.lastname: Koning
mesh_terms: D002384:Catalysis; D006868:Hydrolysis; D007700:Kinetics; D019344:Lactic Acid / Q000737:chemistry / Q000378:metabolism*; D008962:Models, Theoretical; D008970:Molecular Weight; D009010:Monte Carlo Method; D011091:Polyesters / Q000737:chemistry / Q000378:metabolism*; D011100:Polyglycolic Acid / Q000737:chemistry / Q000378:metabolism*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*
chemical_list: D011091:Polyesters; D011108:Polymers; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; C016240:polycaprolactone; D011100:Polyglycolic Acid; D019344:Lactic Acid; C033616:poly(lactide)