Morphological development in absorbable poly(glycolide), poly(glycolide-co-lactide) and poly(glycolide-co-caprolactone) copolymers during isothermal crystallization

Morphological development of the homopolymer, poly(glycolide), PGA; its random copolymers, poly(glycolide-co-lactide), PGA-co-PLA (5:95 and 90:10) and segmented block copolymer, poly(glycolide-co-caprolactone), PGA-co-PCL (75:25) during isothermal crystallization was studied using simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques with synchrotron radiation. It was found that the lamellar morphology could best describe the superstructure of these polymers. During crystallization, both average long period (L) and lamellar thickness (l(c)) exhibited notable decreases with time, which were attributed to the mechanism of secondary crystallization in the form of lamellar-stacks insertion. Both values of L and l(c) were found to increase with temperature. In the chosen crystallization temperature range (100-200 degrees C),]homopolymer PGA exhibited the fastest crystallization rate and the lowest values of L and l(c), probably due to the largest degree of supercooling. As a result, in copolymers with higher content of PGA, the crystallization rate increased and the values of L and l(c) decreased. The value of amorphous layer thickness (l(a)) was the highest in PGA-co-PLA (5:95), but those in PGA, PGA-co-PLA (90:10) and PGA-co-PCL (75:25) were about the same. In addition, the values of L, l(c) and the crystallinity were the highest in PGA-co-PLA (5:95). Corresponding degrees of crystallinity in PGA homopolymer and PGA-co-PCL (75:25) and PGA-co-PLA (90:10) copolymers were relatively low. (C) 1999 Elsevier Science Ltd. All rights reserved.