Preparation of cross-linked aliphatic polyester and application to thermo-responsive material

Abstract

The aim of this study is to investigate the application of a crystalline polymer network to a thermo-responsive material. To achieve this purpose, cross-linked aliphatic polyesters containing a poly-ϵ-caprolactone (poly-CL) segment were prepared from tetrafunctional star-shaped macromonomers. The macromonomers were synthesized by ring-opening polymerization of CL and L-lactide (LA) initiated with pentaerythritol followed by condensation with methacryloyl chloride to introduce a functional group at the chain ends. The cross-linked polyester membranes were prepared by way of a radical polymerization of the macromonomers with visible light irradiation in the presence of initiator and sensitizer. The obtained materials, which consisted of CL homopolymer and LA/CL block copolymer, exhibited a phase transition temperature derived from the melting of polyCL segment. The transition temperatures of the macromonomers and the corresponding cross-linked polyesters depended on the length of poly-CL segment. In order to examine the thermo-responsive properties, the permeation of a model drug, indomethacin, through the membrane composed of cross-linked polyester was investigated by using a 2-chamber diffusion cell. The permeability of the drug increased steeply at around the phase transition with increasing temperature. In addition, the relationship between the degree of crystallinity and the increase of the drug permeability was discussed. From the analysis of permeation profiles, it was revealed that the partition of the drug from the donor phase to the membrane surface considerably increased above the phase transition. Also, the reversible control of the drug permeation through the membrane in response to the repeating temperature change (20°C and 40°C) was observed.