Organocatalytic Approach to Amphiphilic Comb-Block Copolymers Capable of Stereocomplexation and Self-Assembly

Biocompatible amphiphilic block copolymers comprised of poly(ethylene glycol) (PEG) as the hydrophilic component and a poly(methylcarboxytrimethylene carbonate) (PMTC) as a hydrophobic backbone having either poly(L-lactide) (L-PLA) or poly(D-lactide) (D-PLA) branches were prepared by organocatalytic ring-opening polymerization (ROP). The polycarbonate backbone was prepared by copolymerization of two different MTC-type monomers (MTCs) including a tetrahydropyranyloxy protected hydroxyl group, a masked initiator for a subsequent ROP step. Interestingly, the organic catalyst used in the ROP of MTCs was also effective for acetylation of the hydroxyl end-groups by the addition of acetic anhydride added after polymerization. Acidic deprotection of the tetrahydropyranyloxy (THP) protecting group on the carbonate chain generated hydroxyl functional groups that served as initiators for the ROP of either D- or L-lactide. Comb-shaped block copolymers of predictable molecular weights and narrow polydispersities (similar to 1.3) were prepared with up to 8-PLA branches. Mixtures of the D- and L-lactide based copolymers were studied to understand the effect of noncovalent interactions or stereocomplexation on the properties.