Characteristics and Applications of Star-Shaped Architecture for PLA and PGCL

摘要

Lactide was polymerized by stannous octoate in the presence of polyfunctional alcohols such as glycerol and pentaerythritol. The resulting polylactide (PLA) had multi-armed chains to yield a star-shaped architecture. The T_m and degree of crystallinity of star-shaped PLA were lower than those of linear PLA, whereas the hydrolysis rate was enhanced very likely because of the larger number of end groups. It was very beneficial to study the effect of various chain end groups on the thermal and hydrolytic stability of multi-armed PLA. Therefore, the OH terminal groups of multi-armed PLA were converted into Cl, NH_2, and COOH moieties. The melting points and crystallinity of the variously terminated PLA decreased in the order OH > Cl > NH_2 > COOH. The thermal stability was rather poor for OH terminated sample and increased in the order OH COOH < NH_2 ≤ Cl, whilst the hydrolytic stability was least for COOH end group and increased in the order COOH OH < Cl ≤ NH_2. These end group effects were more prominent upon increasing the number of chain arms. The star-shaped architecture was also applied to PGCL for developing a flexible monofilament suture. In the linear copolymerization of PGCL at 170 ℃, r_G and r_(CL) reactivity ratios were calculated from the monomer sequences as 6.84 and 0.13, respectively. This indicates a blocky character of glycolide units, which was confirmed by thermal and crystallographic analysis. Star-shaped PGCL, prepared in the presence of pentaerythritol exhibited lower melting point, crystallinity, and chain orientation than linear PGCL due to the different architecture. Drawn fibres made of star-shaped PGCL are more soft and flexible and show lower modulus and larger elongation than those made of linear PGCL. However, star-shaped PGCL fibres demonstrated enough strength and knot strength and higher degradation rate.