Photopolymerization Induced Phase Separation in (Meth)Acrylate-Based Photopolymers from a Characterization Point of View

Abstract

This work investigates the development of photopolymerization-induced phase separation (PhIPS) in methacrylate-based photopolymers. Bisphenol A ethoxylated dimethacrylate (BisEMA) was copolymerized with a diluted urethane-based diacrylate in isobornyl acrylate (UI) under UV irradiation, using diphenyl-(2,4,6-trimethylbenzoyl) phosphine oxide (TPO) as photoinitiator. Optical changes in the cured copolymers were monitored in real time with a custom setup. NIR-photorheometry, Photo-differential scanning calorimetry, dynamic mechanical analysis, scanning electron microscopy, and atomic force microscopy in both topography and phase imaging modes were employed to characterize the PhIPS effect on network development and microstructure. The correlation between the microstructure of copolymers with varying BisEMA/UI ratios and their bulk properties was studied through tensile and dynstat impact tests. Results showed that up to 20% UI enhances the elongation at break of BisEMA without compromising strength. At higher monomer/oligomer ratios, phase separation led to a strength-ductility trade-off. The study also addresses the influence of AFM sample preparation on correlating phase imaging results to local stiffness distribution.