Aqueous solution behavior of thermoresponsive polyzwitterionic microgels based on poly(N-vinylcaprolactam) synthesized via RAFT precipitation polymerization

Abstract

A new route to synthesize stimuli-responsive poly(N-vinylcaprolactam) (PNVCL) microgels decorated with zwitterionic poly(sulfobetaine) (PSB) chains was developed, using reversible addition–fragmentation chain transfer (RAFT) precipitation polymerization. The polyzwitterionic PSB macro-RAFTs of controlled molecular weight were synthesized by RAFT polymerization of sulfobetaine (SB). Using this method, macro-RAFTs with good control over the molecular weight could be achieved. The PSB macro-RAFTs, having different molecular weights (1000, 5000, 10,000 g/mol) and concentrations (1, 2, 2.5 mol%), were used along with different amount of the cross-linker N,N'-methylenebisacrylamide (BIS) (1.5 and 2.5 mol%) in the precipitation polymerization of PNVCL microgels to obtain varying amounts of surface-grafted polyzwitterionic chains of controlled length and variable cross-linking degrees. The successful incorporation of PSB macro-RAFTs into PNVCL microgels was characterized by FTIR and 1H NMR studies. Increasing the PSB concentration and BIS content in the PNVCL microgels resulted in a linear increase in electrophoretic mobility (µe) and volume phase transition temperature (VPTT). However, increasing the molecular chain length of the zwitterionic macro-RAFT resulted in a shift of VPTT towards lower temperatures. This kind of stimuli-responsive, polyzwitterion decorated PNVCL microgels can be a potential material for biomedical applications.