Crystallisation and morphology of neat and degraded poly(p-dioxanone)

The present work compares the morphology and crystallisation kinetics of ne at and hydrolytically degraded poly(p-dioxanone), PPDX. The hydrolytic degr adation was performed in a phosphate buffered saline solution (0.2 M, pH 7. 4) at 37 degreesC. The spherulitic morphology and the isothermal spheruliti c growth rate were studied by optical microscopy while the overall crystall isation rate was determined by DSC. A thermal fractionation procedure was a pplied to the samples using the successive self-nucleation and annealing (S SA) protocol. The results indicate that the peculiar spherulitic morphologi es exhibited by neat PPDX change as a function of molecular weight loss, bu t this change can be qualitatively rationalised as a function of the appare nt supercooling applied to the crystallising sample. A change in growth reg ime with supercooling (from regime II to regime III) was detected using Hof fman's kinetic crystallisation theory for neat and degraded PPDX. It was fo und that both the overall crystallisation rate and the spherulitic growth r ate were substantially increased as the molecular weight was decreased by h ydrolytic degradation. The SSA results indicate that degradation depletes t he longest chains within the molecular weight distribution of neat PPDX fir st, a fact consistent with an initial attack of the amorphous regions of th e sample. (C) 2001 Elsevier Science Ltd. All rights reserved.