Effects of substitution groups on the RAFT polymerization of N-Alkylacrylamides in the preparation of thermosensitive block copolymers

Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to prepare a series of homo- and copolymers of N-alkyl-substituted acrylamides. The acrylamide monomers have similar chemical structures, but they all exhibit difference in reactivities, especially between N-monosubstituted and N,N-disubstituted acrylamides during the RAFT process. Results from size exclusion chromatography and matrix-assisted laser desorption ionization time-of-flight mass spectrometry indicate chain transfers to monomers are easier to occur for N-monosubstituted polyacrylamides, with negative deviations of the molecular weights from the theoretical values. The high transfer activity makes them good macro-chain transfer agents (CTAs). The stronger electron-donating conjugative effect renders the disubstituted acrylamides more reactive, meaning that they can react more readily with monosubstituted polyacrylamide-CTAs to form a sequent block. Tri- and tetrablock copolymers with multiple thermosensitivity have been successfully prepared and tested following these guiding principles.