Orthogonally grown polycarbonate and polyvinyl block copolymers from mechanistically distinct (co)polymerizations

Abstract

Mechanistically distinct polymerization systems can afford unique block copolymers that would not be accessible by mere sequential polymerization. Herein we report a convenient one-pot synthesis of miscellaneous di- and triblock copolymers comprising CO₂-based and polyvinyl blocks, obtained orthogonally through triethylborane (TEB)-mediated ring opening copolymerization (ROCOP) of CO₂ with epoxides on the one hand and reversible addition fragmentation chain transfer (RAFT) polymerization of vinyl monomers on the other. 4-Cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl] pentanoic acid (TTC-COOH), which carries a trithiocarbonate function and a carboxylic acid group, played the dual role of a chain transfer agent for RAFT polymerization and an initiator for the ROCOP of CO₂/epoxide. Different bases such as tetrabutylammonium hydroxide, N-heterocyclic carbene (NHC), and tributylamine (TBA) were used for the deprotonation of TTC-COOH; in each case the compatibility of the generated carboxylic salts with trithiocarbonate functions was checked when they were utilized to copolymerize CO₂ and epoxides. It was found that the salts produced in situ by the deprotonation of TTC-COOH using NHC and TBA did not harm trithiocarbonate functions. The two distinct polymerizations occurred as expected, affording a series of well-defined CO₂-based AB and ABC block copolymers comprising one or two poly(vinyl) blocks, depending upon the choice of different combinations of epoxides and vinyl monomers. The thermal characterization of these AB and ABC block copolymers revealed either two or three glass transition temperatures indicative of phase-separated materials.