Renewable Rosin Acid-Degradable Caprolactone Block Copolymers by Atom Transfer Radical Polymerization and Ring-Opening Polymerization

Renewable rosin acid-degradable caprolactone block copolymers were prepared by atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP). Two-step sequential polymerization using either poly(2-acryloyloxyethyl dehydroabietic carboxylate)-OH (PAEDA-OH) or poly(epsilon-caprolactone)-Br (PCL-Br) as macroinitiators resulted in well-defined block copolymers with low polydispersity. One-pot polymerization was carried out with three different sequential feeds of AEDA and epsilon-CL monomers. The control of one-pot polymerization depended on the interactions of coexisting ATRP catalysts and ROP catalysts. While the minimal interactions between copper(I) and tin(II) catalysts produced well-defined block copolymers, excess copper(II) or tin(II) led to the formation of block copolymers with polydispersity > 1.5. It was suggested that the tin(II) catalysts reduced the persistent radicals copper(II) of ATRP, leading to a poorly controlled polymerization. PCL segments of the block copolymers exhibited excellent degradability under acidic conditions. Thermal behaviors of these block copolymers showed a strong dependence of polymer compositions due to the possible crystallization of the PCL block.