Dual Switching in Both RAFT and ROP for Generation of Asymmetric A²A¹B¹B² Type Tetrablock Quaterpolymers

In reversible addition-fragmentation chain transfer (RAFT) polymerization, monomers are divided into "more-activated" monomers (type-A¹ monomer) and "less-activated" monomers (type-A² monomer). In ring-opening polymerization (ROP), monomers are considered to fall into electrophilically polymerizable monomers (lactones and carbonates, type-B¹ monomer) and nucleophilically polymerizable monomers (lactides and carbonates, type-B² monomer). Developing a strategy to copolymerize the four kinds of monomers for formation of asymmetric A²A¹B¹B² type tetrablock quaterpolymers by one-pot sequential ROP and RAFT polymerization is a challenge. Herein, we designed and synthesized a molecule, 2-hydroxyethyl 2-(methyl(pyridin-4-yl)carbamothioylthio)propanoate, which functioned as a trifunctional initiator, to initiate ROPs and to modulate RAFT polymerizations sequentially in one-pot. We proposed a dual "acid/base switch" strategy in both RAFT polymerizations and ROPs for one-pot generation of asymmetric A²A¹B¹B² type tetrablock quaterpolymers. A series of di-, tri-, and tetrablock copolymers were synthesized and showed predicted molar mass and narrow dispersities, manifesting that the ROPs and RAFT polymerizations proceeded independently in controlled manners. The dual "acid/base switch" strategy paved a new avenue to combine RAFT polymerizations and ROPs for synthesis of designed copolymers with advanced functionalities and architectures.