Physical properties of poly(ε-caprolactone) coalesced from its α-cyclodextrin inclusion compound

Poly(epsilon-caprolactone)(PCL) is a biodegradable/bioabsorbable polyester used in such biomedical applications as drug delivery and suture manufacturing. PCL has relatively poor physical properties, however, limiting its load-bearing applications. In this work, PCL was processed with alpha-cyclodextrin (alpha-CD) to form an inclusion complex (IC). The host alpha-CD was then stripped away to yield bulk PCL with largely extended, un-entangled polymer chains, a process referred to as coalescence. The changes in thermal, physical, and solid-state rheological properties resulting from this coalescence process were examined. It was found that elongating and un-entangling the PCL chains in this manner resulted in substantial increases in melt-crystallization temperatures, T(C)s, up to 25 degrees C, depending on the cooling rate from the melt. Coalescence also increased the elastic storage modulus, decreased tan delta, increased the average hardness and Young's modulus by 33 and 53%, respectively, and produced a closer packing of chains in the non-crystalline sample regions, without affecting the overall PCL crystallinity. Interestingly, the reorganized PCL chains in the non-crystalline regions of coalesced samples did not revert to the normal randomly-coiled entangled melt even after heating well above T-m (90 degrees C) for a month. The addition of small amounts (a few wt%) of coalesced PCL was also found to effectively nucleate the melt-crystallization of as-received PCL Thus, the semi-crystalline morphology of PCL may be controlled by melt-processing with coalesced PCL added as a nucleant, that is not only necessarily non-toxic and biodegradable/bioabsorbable, but is also chemically compatible. (C) 2011 Elsevier Ltd. All rights reserved.