Gelation of RAFT polymer networks analysed by rheology

Abstract

Reversible addition-fragmentation chain-transfer (RAFT) polymerization is used to make polymer networks with improved homogeneity. Network formation is mostly inferred from the characterization of macro-indicators, such as vinyl bond conversion for kinetics data and swelling ratio for degree of crosslinking, which offer little information on micro-structure and homogeneity. To better probe the formation and structure of RAFT polymer networks during gelation, dynamic analysis was performed in situ using an advanced rheometer. In agreement with previous investigations, the time to gelation of the RAFT networks was prolonged in relation to free-radical polymerized (FRP) networks. It was found that the loss modulus (G″) of the RAFT networks was lower than that of FRP networks, indicating less friction from fewer microgel defects. The loss factor tan δ of the RAFT networks was quasi-steady, suggesting good retention of ideally elastic properties. In the vicinity of the gel point, the RAFT networks showed a prominent loss modulus (G″) local maximum phenomenon.