Morphology and dynamics of the poly(epsilon-caprolactone)-b-poly(L-lactide) diblock copolymer and its inclusion compound with alpha-cyclodextrin: A solid-state C-13 NMR study

摘要

A biodegradable diblock copolymer of poly(epsilon-caprolactorie) (PCL) and poly (L-lactide) (PLLA) was synthesized and characterized. The inclusion compound (IC) of this copolymer with a-cyclodextrin (alpha-CD) was formed and characterized. Wide-angle X-ray diffraction showed that in the IC crystals alpha-CDs were packed in the channel mode, which isolated and restricted the individual guest copolymer chains to highly extended conformation. Solid-state C-13 NMR techniques were used to investigate the morphology and dynamics of both the bulk and alpha-CD-IC isolated PCL-b-PLLA chains. The conformation of the PCL blocks isolated within the a-CD cavities was similar to the crystalline conformation of PCL blocks in the bulk copolymer. Spin-lattice relaxation time (T1C) measurements revealed a dramatic difference in the mobilities of the semicrystalline bulk copolymer chains and those isolated in the a-CD-IC channels. Carbon-observed proton spin-lattice relaxation in the rotating frame measurements (T1 rhoH) showed that the bulk copolymer was phase-separated, while, in the IC, exchange of proton magnetization through spin-diffusion between the isolated guest polymer chains and the host a-CD was not complete. The two-dimensional solid-state heteronuclear correlation (HetCor) method was also employed to monitor proton communication in these samples. Intrablock exchange of proton magnetization was observed in both the bulk semicrystalline and IC copolymer samples at short mixing times; however, even at the longest mixing time, interblock proton communication was not observed in either sample. In spite of the physical closeness between the isolated included guest chains and the host alpha-CD molecules, efficient proton spin diffusion was not observed between them in the IC. (c) 2005 Wiley Periodicals, Inc.