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

Abstract

Statistical networks of butyl acrylate and 1,4‐butanediol diacrylate are photopolymerized in bulk, both in the presence and absence of the RAFT agent EPHT. The amounts of crosslinker and RAFT agent are varied. The Young's moduli of the RAFT networks are always lower than those of conventionally obtained networks. With increasing amounts of RAFT agent, the Young's modulus decreases and the strain at break values increase, respectively. The network density, the apparent molar mass of the network chains and the swelling show significant differences between RAFT‐ and conventionally obtained networks. The degree of swelling and the amount of extractable polymer increase largely with the amount of RAFT agent. Kinetic DSC measurements show that the gel point is delayed with increasing amounts of RAFT agent. In addition, a rate retardation effect with increasing RAFT agent concentration is observed.

Investigation on the homogeneity of PMMA gels synthesized via RAFT polymerization

“…The samples obtained via conventional free radical polymerization (RAFT concentration zero) show the highest moduli. These findings are in agreement with several previous studies which also revealed lower moduli for gels obtained by controlled radical polymerization [11,12,15].…”

“…The data seem to follow a single curve irrespective of how the synthesis was performed, with some scatter presumably due to experimental uncertainty. Similar results regarding the swelling properties of RAFT polymerized networks have been obtained before by Crescenzi et al [11], Henkel and Vana [12] and Lu et al [17].…”

“…Recently, Henkel and Vana reported on networks made of butyl acrylate and 1,4-butanediol diacrylate in bulk. They obtained smaller values of the Young's modulus for RAFT polymerized systems in comparison to FRP, unless the content of cross-linker was very high [12]. Similar findings were reported by Yu et al [15] and Crescenzi et al [11] on RAFT polymerized networks, whereas Yu et al [10] obtained comparable values in the case of ATRP.…”

“…Some of the observations leading to this notion have been considered in the literature before [2,6,11,12,15]. Nevertheless, these authors still argue that gels obtained by CRP are more homogeneous than those synthesized by FRP.…”

“…Since the CRP networks are usually less densely cross-linked, they exhibit higher swelling ratios than those obtained by FRP [2,11,12,16,17].…”