Synthesis of Repeating Sequence Copolymers of Lactic, Glycolic, and Caprolactic Acids

Repeating sequence copolymers of poly(lactic-co-caprolactic acid) (PLCA), poly(glycolic-co-caprolactic acid) (PGCA), and poly(lactic-co-glycolic-co-caprolactic acid) (PLGCA) have been synthesized by polymerizing segmers with a known sequence in yields of 50-85% with M(n)s ranging from 18-49 kDa. The copolymers exhibited well-resolved NMR resonances indicating that the sequence encoded in the segmers used in their preparation is retained and that transesterification is minimal. The exact sequences allowed for unambiguous assignment of the NMR spectra, and these standards were compared with the data previously reported for random copolymers. The glass transition temperatures (T(g)s) of the PLCA and PGCA copolymers were found to depend primarily on monomer ratio rather than sequence. Sequence dependent T(g)s were, however, noted for the PLGCA polymers with 1:1:1 L:G:C ratios; poly LGC and poly GLC exhibited T(g)s that differed by nearly 8 degrees C. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49:1847-1855, 2011