Cationic copolymerization of ε-caprolactone and L,L-lactide by an activated monomer mechanism Part A Polymer chemistry

The cationic homopolymerization and copolymerization of L,L-lactide and e-caprolactone in the presence of alcohol have been studied. The rate of homopolymerization of e-caprolactone is slightly higher than that of L,L-lactide. In the copolymerization, the reverse order of reactivities has been observed, and L,L-lactide is preferentially incorporated into the copolymer. Both the homopolymerization and copolymerization proceed by an activated monomer mechanism, and the molecular weights and dispersities are controlled {number-average degree of polymerization = ([M]₀ − [M]t)/[I]₀, where [M]₀ is the initial monomer concentration, [M]t is the monomer concentration at time t, and [I]₀ is the initial initiator concentration; weight-average molecular weight/number-average molecular weight ∼1.1-1.3}. An analysis of ¹³C NMR spectra of the copolymers indicates that transesterification is slow in comparison with propagation, and the microstructure of the copolymers is governed by the relative reactivity of the comonomers.