Abstract: In this paper, a AB type of amphiphilic diblock copolymer, composed of methoxy-poly(ethylene glycol) (MeOPEG) as the hydrophilic block and poly(εcaprolactone-co-d, l-lactide) (P(Cap-co-LL)) as the hydrophobic block were synthesized by bulk ring-opening copolymerization using MeOPEG as initiator and LL and Cap as comonomers. The chemical structure of the diblock copolymer MeOPEG-P(Cap-co-LL) was studied by ¹H NMR, ¹³C NMR and HMBC. It was found that random copolymerization of Cap and LL occurred in the formation of P(Cap-co-LL) blocks. The transesterification behavior between the Cap units and the LL units and that between the d-lactide unit and the l-lactide unit in P(Cap-co-LL) were investigated. The yield of the transesterification, the randomness of P(Cap-co-LL) blocks and the average length of caproyl segments and lactidyl segments were calculated using the Bernoulli statistics theory and ¹³C NMR spectra. It was found that both the yield of the transesterification and the randomness of P(Cap-co-LL) block were the highest when the mass ratio of LL to Cap was close to 1∶1. It was also shown that the synthesis condition and the feeding ratio of P(Cap-co-LL) segments have important influences on the transesterification extent, randomness of P(Cap-co-LL) blocks and the average length of caproyl segments and lactidyl segments.

Key words: NMR, chain structure, HMBC, amphiphilic diblock copolymer, transesterification