Synthesis of Dendrigraft Poly(ε-Caprolactone)s Using Side Hydroxyl Groups for the Grafting of Branch Chains

Dendrigraft poly(epsilon-caprolactone)s with high molecular weight and narrow polydispersity are synthesized via a convenient generation-growth approach. Copolymerization of epsilon-caprolactone (CL) and 4-(2-benzoxyethoxy)-epsilon-caprolactone (BECL) with stannous octanoate as a catalyst affords a functionalized poly(epsilon-caprolactone) (PCL) with benzyl-protected hydroxyl side groups. After removal of benzyl groups by palladium-catalyzed hydrogenolysis, the graft copolymerization of CL and BECL onto the hydroxyl-bearing linear polyester (zero-generation) affords the first-generation graft polyester. Further deprotection and graft polymerization cycles led to dendrigraft polyesters. Molecular weights are multiplied in each graft copolymerization. The second-generation dendrigraft poly(epsilon-caprolactone) has an Mw of 236 000 g center dot mol-1 and Mw/Mn of 1.53.