CHARACTERIZATION ON THE CHAIN HETEROGENEITY OF L-LACTIDE AND epsilon-CAPROLACTONE COPOLYMERS

Molecular chain heterogeneity of the copolymer of L-lactide and epsilon-caprolactone (PLC) was investigated using the preparative temperature rising elution fractionation (TREF) technique and successive self-nucleation/annealing (SSA) thermal fractionation. Two PLC samples with epsilon-caprolactone compositions of 5 mol% and 10 mol% were prepared and fractionated by using TREF. For both samples, three fractions were collected and characterized with nuclear magnetic resonance spectroscopy (H-1-NMR) and gel permeation chromatography (GPC). The H-1-NMR results showed that there exists obvious differences in the caproyl content among the fractions. It was also found, With GPC method, that for the fraction of higher elution temperature, the number average molecular weight (M-n) is higher and the distribution is narrower. The data obtained suggest that the fractionation is mainly the result of the difference of the chain tacticity. The chain heterogeneity of TREF fractions was further analyzed with SSA thermal fractionation. The first T-s to be used in the SSA method was carefully chosen in Domain II for all fractions. After SSA treatment, the appearance of multiple melting behavior for each fraction indicates that a heterogeneous intramolecular distribution of defects still exsits in the chains of fractionated sample. On the other hand, the intermolecular heterogeneity is evident in the different melting ranges of each fraction.