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

Abstract

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 amount of microgel formation.

Electrochemically Mediated Reversible Addition–Fragmentation Chain-Transfer Polymerization

“…40–42 However, an electrochemically mediated RAFT ( e RAFT) is more challenging than e ATRP. Cu/L complexes for ATRP have a well-defined and reversible redox behavior, 43 whereas the electrochemical reactivity of RAFT agents is mostly unexplored, and could result in irreversible redox processes that cannot be exploited to generate radicals.…”

The Influence of RAFT on the Microstructure and the Mechanical Properties of Photopolymerized Poly(butyl acrylate) Networks

“…Zhu and co‐workers found both in experiments using mechanical spectroscopy on oligo(ethylene glycol) dimethacrylates and in corresponding simulations that networks, which were generated via the RAFT process, exhibit an increased homogeneity. We ourselves found that thin hydrogel films of the thermoresponsive polymer poly( N ‐isopropylacrylamide) (pNIPAm), prepared by electrochemically triggered RAFT polymerization, show a strongly enhanced homogeneity of the hydrogel surfaces as studied by AFM . Photocrosslinking, however, appears to be of higher industrial importance and in the field of UV‐initiated crosslinking RAFT polymerizations, systems with multifunctional methacrylates were studied by Zhuo et al, who found that the RAFT process has a considerable influence on the curing kinetics.…”

Surface Initiated Polymerizations via e-ATRP in Pure Water

“…It allowed for the modification of proteins in order to tailor new hybrid materials [23][24][25]. Recently a new impulse has been given to ATRP by controlling the reaction using electrochemistry, so-called e-ATRP which had was previously also attempted in combination with reversible addition-fragmentation chain transfer (RAFT) polymerization [26]. By adjusting the electrochemical potential, this method reduces Cu(II) to Cu(I) in-situ and thereby controlling the amount of Cu(I) in the system, and hence control over the polymerization reaction even in combination with the presence of oxygen which was previously only possible with activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP) [27,28].…”