One-pot synthesis of comb-like copolymer bearing side chains composed of branched and linear polylactides

Ethyl cellulose (EC), lactide (LA) and branching comonomer 2,2-bis(hydroxymethyl) butyric acid (BHB) were copolymerized in xylene using Sn(Oct)2 as catalyst. Catalyst amount and polymerization temperature were optimized for the effective introduction of certain amount of branched polylactide (PLA) into the side chains of comb-like copolymers having EC backbone. The characterization of the obtained copolymers by GPC and 1H NMR demonstrated that the influence of polymerization temperature in the range of 110-150 °C on the efficient incorporation of branching units was not pronounced, whereas high amount of catalyst was the key point. The content of branching units in the copolymers could be enhanced by increasing the feed amount of BHB monomer. A plausible mechanism for the polymerization was proposed according to the model experiments. Compared with the comb-like copolymers with merely linear PLA side chains, the ones bearing both branched and linear PLA side chains had the following characters: (1) better solubility in the polar solvent of ethanol; (2) much faster hydrolysis degradation. These characters became more pronounced when the content of branching units in the side chains increased.