An Exploration of the Universal and Switchable RAFT-Mediated Synthesis of Poly(styrene--maleic acid)--poly(-vinylpyrrolidone) Block Copolymers.

The synthesis of poly(styrene--maleic anhydride) (SMAnh) and poly(4--butylstyrene--maleic anhydride) (BuSMAnh) macro-RAFT agents was investigated using universal 3,5-dimethylpyrazole dithiocarbamate and stimuli-responsive -(4-pyridinyl)--methyldithiocarbamate RAFT agents. SMAnh/BuSMAnh macro-RAFT agents of targeted molecular weight and narrow molecular weight distribution could be synthesized with intentional variation of the terminal monomer unit, allowing for the assessment of two distinctive macro-R-groups. SMAnh macro-RAFT agents were utilized to mediate the thermally initiated polymerization of -vinylpyrrolidone (NVP), yielding SMAnh--PVP, but with significant thermolysis and hydrolysis of dithiocarbamate ω-chain ends. Alternatively, the redox-initiated RAFT-mediated polymerization of NVP at ambient temperatures using hydrolyzed macro-RAFT agents, i.e., poly(styrene--maleic acid) (SMA) and poly(4--butylstyrene--maleic acid) (BuSMA), was explored. Double hydrophilic SMA--PVP and BuSMA--PVP block copolymers could be synthesized but with significant broadening of the molecular weight distribution. This is a result of the formation of dead chains derived from the alkaline hydrolysis of macro-RAFT agents prepolymerization and hydrolysis of dithiocarbamate chain ends throughout the polymerization. The latter is exacerbated by the insertion of NVP at the ω-chain end, which was subsequently investigated via the kinetic analysis of the xanthate- and dithiocarbamate-mediated aqueous homopolymerization of NVP.