Comparative thermal degradation studies on glycolide/trimethylene carbonate and lactide/trimethylene carbonate copolymers

Thermal degradation of the glycolide/trimethylene carbonate copolymer used for bioabsorbable surgical sutures (Maxon (TM)) has been studied by isothermal and nonisothermal methods. Thermal decomposition always follows a single mechanism, although some differences have been found between the two performed analyses. Degradation of the sample has also been compared in both an inert (N-2 and an oxidative (air) atmosphere. In all cases, the activation energy is close to 115-119 kJ/mol. A lactide/trimethylene carbonate copolymer (PLAC/PTMC) with a similar molar content of trimethylene carbonyl units to that of the indicated suture has been synthesized and characterized. Differences in the monomer reactivities have allowed to obtain a copolymer with blocky distribution of lactidyl units. Thermal decomposition of PLAC/PTMC takes place in two steps, the first one corresponding to a preferential loss of lactidyl units. Nonisothermal isoconversional methods were used to obtain the kinetic parameters of each degradation step. The complete kinetic triplets of the two studied copolymers have been determined by the Coats-Redfern and the invariant kinetic parameters (IKP) methodologies and the results were compared. (c) 2007 Wiley Periodicals, Inc.