Thermoplastic elastomer obtained by photopolymerization-induced concomitant macrophase and microphase separations

We report on concomitant photoinitiated polymerization-induced macrophase and microphase separation strategies to produce hierarchically structured recyclable poly(n-butyl acrylate) based elastomeric materials. The investigated crosslinker-free formulations are composed of n-butyl acrylate monomer and a UV photo-initiator mixed with poly(methyl methacrylate)-b-poly(n-butyl acrylate)-poly(methyl methacrylate) ABA triblock copolymers. Two different pre-synthesized copolymers are used to control the macrophase separation. One synthesized by nitroxide-mediated radical polymerization (NMRP), and a second by anionic polymerization (AP). Essentially, NMRP route leads to copolymer with unsaturated chain ends, activated during UV photopolymerization. On the other hand, the copolymer synthesized by AP are chemically inert. That dissimilarity is also highlighted by time-resolved FTIR and SAXS, performed to monitor respectively monomer conversion and nanostructure evolution during photopolymerization. The experimental data demonstrate that the reactivity of the triblock copolymer impacts drastically the polymerization kinetics and the self-assembly processes. Finally, the rheological analysis shows that the produced materials present a solid-like behavior at low frequencies despite a large PnBA content (i.e., 85 wt%). This property is associated to the phase segregation and to the sample hierarchical morphology. image