Phase-separated polymers have been used in many applications due to their controllable thermomechanical and optical properties. This work studies photo-induced phase separation in highly-crosslinked hybrid systems as a function of polymerization temperature to modulate the reaction rate of each component. These rates in turn lead to specific polymer with dual phase morphologies. With inherently fast gelation of these systems, phase separation is enabled based on polymer immiscibility and orthogonal chemistries which lead to thermodynamic instability during photopolymerization. The formation of multiple domains is controlled by monomer composition and reaction temperature. Our investigation shows that phase-separated domains are formed when photocuring at room temperature. At higher reaction temperatures, both monomers approach similar photopolymerization rates. These matching rates may enhance the miscibility of monomers, resulting in interpenetrating polymer networks. Interestingly, at increased reaction temperature our experiments show even more segregated domains, with the glass transition temperature of the harder domain shifted to a higher temperature. This behavior is attributed to the delay of gelation which allows more diffusion and higher degree of phase separation. Additionally, these phase-separated polymers demonstrate a reduction in material gloss by 50% when compared to systems with neat monomers. It is reasonable to believe that the nanoscale domains formed in these systems scatter the light in all directions, resulting in a significant reduction of gloss. We will also discuss changing the order of cure, specifically where the diepoxide is initially thermally-cured, followed by photopolymerization of dimethacrylate to alter photopolymerization kinetics and the formation of phase-separated domains. Due to the faster formation of the softer diepoxide domain, these materials show significantly higher elongation at break. Moreover, we show that phase separation facilitates reduction of photopolymerization shrinkage stress. We show that morphology and properties of highly crosslinked systems can be controlled via photo-induced phase separation by changing reaction temperature or curing order. This investigation will lead to phase separated materials with controlled anti-reflectance properties and reduced photopolymerization shrinkage stress.

Photo-Induced phase separation in dimethacrylate/diepoxide systems using different reaction temperatures and curing methods

2019 Spring National Meeting

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