Electrochemically Induced RAFT Polymerization of Thermoresponsive Hydrogel Films: Impact on Film Thickness and Surface Morphology

Thin hydrogel films of the thermoresponsive polymer poly(N-isopropylacrylamide) (pNIPAm) were prepared by electrochemically triggered reversible addition-fragmentation chain transfer (RAFT) polymerization. Two different RAFT agents were employed, which work in either acidic or basic solution. In both cases, addition of RAFT agents had an influence on the thickness and the surface morphology of the films. At low concentration, the polymerization efficiency increased. At high concentration, the efficiency decreased at acidic pH, while it remained constant under basic conditions. Neither RAFT agent displayed electrochemical activity on its own, but they did modify the electrochemical behavior of the initiator. The addition of RAFT agent strongly enhances the homogeneity of the hydrogel surfaces, which presumably is due to a reduced electrochemically triggered RAFT polymerisation amount of microgel formation.