Kinetically Controlled Photoinduced Phase Separation for Hybrid Radical/Cationic Systems
2019
Hasa, Erion | Scholte, Jon P. | Jessop, Julie L. P. | Stansbury, J. W. | Guymon, C Allan
Controlling phase separation in polymer systems has shown significant promise in combining properties of different components into an integrated polymer system. In this work, we investigate the effect of photoinduced phase separation on polymer morphology and properties in hybrid radical/cationic systems composed of butyl acrylate (BA) and difunctional oxetane (DOX). We show that the irradiation intensity has a significant effect on the formation of phase-separated domains. By increasing the irradiation intensity at fixed co-monomer composition, the morphology changes from one with a continuous soft 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 because of fast photopolymerization, which significantly limits monomer/polymer diffusion. The smaller domain size enhances the flexibility and strength of the phase-separated polymers. On the other hand, the irradiation intensity has little to no effect on the polymer structure or properties for systems that do not phase-separate. Dynamic mechanical analysis demonstrates that phase separation associated with higher irradiation intensity during cure contributes to a 40-fold increase in toughness and up to fivefold higher elongation at break. This behavior is attributed to the formation of polymers with co-continuous hard/soft domains and decreased domain size. This study demonstrates that the morphology and properties of photoinduced phase-separated materials can be controlled by altering the initiation irradiation intensity for hybrid radical/cationic materials.
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