Polymerization-induced phase separation has shown promise in generating materials with controllable morphology and mechanical properties. In this work, we show that irradiation intensity and formulation chemistry allow direct control of phase separation in photo-cured hybrid radical/cationic systems. Our investigation reveals that irradiation intensity has a deterministic effect on the formation of phase-separated domains. By increasing the irradiation intensity in butyl acrylate (BA) and di-oxetane (DOX) photopolymerizations, the morphology changes from one with a continuous softer BA domain to one with co-continuous BA (soft) and DOX (hard) domains. At higher irradiation intensity, the domain size of each phase is decreased due to fast photopolymerization which limits significantly monomer/polymer diffusion. On the other hand, irradiation intensity has little to no effect on polymer structure and mechanical properties for systems with low concentrations of BA as no phase separation is observed. Dynamic mechanical analysis demonstrates that phase separation in systems dramatically enhances mechanical properties such as Young’s modulus and elongation at break when the irradiation intensity is increased. The extent of phase separation is controlled further by incorporating multi-functional monomers that either cross-link the soft acrylate domain or connect the hard and soft domains using a hybrid acrylate-oxetane monomer. Atomic force microscopy shows that the domain size of the harder oxetane phase reduces with increasing crosslinker concentration because of faster gelation. Phase separation is maintained for up to 3 wt% crosslinker concentration but is significantly suppressed with very small phase-separated domains at higher crosslinker concentrations. Interestingly, an approximately three-fold increase in toughness is observed with higher elongation at break due to small hard and soft domains facilitated by controlled cross-linking and photo-cure intensity. These results demonstrate the ability to control the morphology and thereby significantly enhance properties of radical/cationic systems through photopolymerization-induced phase separation by modulating irradiation intensity and cross-linker design.

Controlled phase separation and thermo-mechanical properties in hybrid radical/cationic systems using photopolymerization

2019 Spring National Meeting

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