Initiator structure influence on thermal and rheological properties of oligo(epsilon-caprolactone)

Biodegradable thermoplastic oligomers have potential as biomaterials for tissue augmentation and drug-delivery applications. One means of obtaining such a biomaterial is through the ring-opening polymerization of epsilon-caprolactone using an alcohol initiator. In this paper we continue to examine the influence of the structure of the initiator used on the thermal and rheological properties of oligo(epsilon-caprolactone). Specifically, primary and secondary pentanol, and cis- and trans-pentenol were studied as initiators in the preparation of oligomers of constant molecular weight. In agreement with previous work, the secondary conformer yielded higher melt viscosities, lower degrees of crystallinity and lower glass transition temperatures. The cis conformer produced the lowest melt viscosity; however, the activation energy for flow was higher than obtained previously with oleyl alcohol. This result was attributed to the alkane chain lengths on either side of the cis double bond in the initiator. The order of melt viscosity increased with initiator conformer as follows: cis, trans, primary and secondary. The results were explained in terms of oligomer chain flexibility in the melt.