From Click Chemistry to Cross-Coupling: Designer Polymers from One Efficient Reaction
Palladium-catalyzed Suzuki−Miyaura cross-coupling was demonstrated to be a versatile reaction platform to install functional groups onto well-defined polymers derived from reversible addition−fragmentation chain-transfer (RAFT) polymerization. Cross-coupled products were achieved utilizing a range of functional boronic acids including, but not limited to, furan, alkyloxyphenyl, methacrylamide, trifluorophenyl, anthracene, and dimethylaminophenyl. High to quantitative degrees of functionalization were obtained by employing convenient reaction conditions at low to moderate temperatures (23−60 °C), within short reaction times (2−16 h), while using air-stable reagents at 1.5−3.0 equiv. of boronic acid. Specifically, a custom monomer, N-[2-(4-bromophenyl)ethyl]acrylamide (BPEA), was synthesized bearing a reactive handle for subsequent cross-coupling, and its chemical structure was verified using nuclear magnetic resonance. RAFT polymerization of BPEA revealed attributes of a successful reversible-deactivation radical polymerization (RDRP) yielding polymers with predetermined molecular weights and narrow dispersity values (Đ < 1.3). The retention of living chain ends was evidenced by efficient chain extension of poly(BPEA) with N-isopropylacrylamide producing a low dispersity diblock copolymer. Optimal functionalizations were found to be achieved through removal of the RAFT chain transfer agent and, in specific instances, by functionalizing statistical copolymers. The utility of this functionalization strategy, when combined with RDRP, has the ability to provide potentially thousands of structurally diverse functionalized polymers, elucidate quantitative structure−property relationships, and create new avenues to advanced polymeric architectures.