Seongnam Lee

Effect of Composition and Synthetic Route on the Microstructure of Biodegradable Diblock Copolymer, Poly(ε-caprolactone-co-L-lactide)-b-Poly(ethylene glycol)

Biodegradable poly(ε-caprolactone-co-L-lactide)-b-poly(ethylene glycol) (PCLA-b-PEG) copolymers were synthesized via solution polymerization by varying the feed composition of ε-caprolactone (ε-CL) and L-lactide (LLA) (ε-CL: LLA=10∶0, 7∶3, 5∶5, 3∶7, 0∶10). The feed ratio based on weight is in accordance with the copolymer composition except for the case of ε-CL: LLA=3:7 (C3L7), which was verified by1H-NMR. Two different approaches were used for the exceptional case, which is an extension of the reaction time or the sequential introduction of the monomer. A copolymer composition of ε-CL: LLA=3:7 could be obtained in either case. The chemical microstructure of PCLA-b-PEG was determined using the13C-NMR spectra and the effect of the sequential structure on the thermal properties and crystallinity were examined. Despite the same composition ratio of the copolymer, the microstructure can differ according to the reaction conditions.

Effect of Plasticization of Poly(Vinyl Cinnamate) on Liquid Crystal Orientation Stability

A cinnamate group is a well-known compound group used in the dimerization reaction by ultraviolet irradiation, and cinnamate polymers are studied as photoalignment materials. In this study, the radical reaction of cinnamate side groups attached to a flexible polymer backbone is considered feasible using thermal energy. To induce the thermal reaction of cinnamate side groups, we modified the flexibility of poly(vinyl cinnamate) by introducing a plasticizer into the polymers and investigated the thermal reaction behavior of cinnamate side groups. The plasticization of poly(vinyl cinnamate) makes the induction of the thermal reaction of cinnamate side groups easier than that of unmodified poly(vinyl cinnamate). The thermal reaction of cinnamate side groups is closely related to the enhancement of the thermal stability of the liquid crystal orientation of polymer films with polarized UV irradiation.