Manipulation of crosslinking in photo-induced phase separated polymers to control morphology and thermo-mechanical properties

Photopolymerization-induced phase separation allows significant control over polymer morphology and properties for hybrid radical/cationic systems. Polymer nano/micro-structure and domain size/continuity of each incompatible phase can be manipulated by using different photopolymerization conditions and formulation chemistries. In this work we incorporate multifunctional monomers including hexanediol diacrylate (HDDA) and a hybrid acrylate-oxetane monomer (OXMA) to modify the domain size scale and phase-separated morphology of a butyl acrylate (BA) and difunctional oxetane (DOX) system. Photopolymerization of the DOX/BA system results in distinct and co-continuous soft acrylate and hard oxetane domains. Incorporating different amounts of HDDA or OXMA generates polymer morphologies with smaller size-scale continuous hard domains because of the reduction in time difference between phase separation onset and gel point. Additionally, thermomechanical analysis shows that two glass transition temperatures (Tg's) are created for the DOX/BA system as indicated by the tan(δ) profiles, confirming the formation of distinct phase-separated domains. The addition of a crosslinker significantly increases the Tg of acrylate-rich domain as much as 45 °C, forming less distinct and broad tan(δ) peaks. The formation of more integrated as well as small and continuous domains enhances the flexibility and strength of the phase-separated DOX/BA system. A 2-fold increase in both elongation at break and maximum stress is observed with the addition of small amounts of HDDA or OXMA, resulting in an almost 5-fold increase in toughness and 2-fold increase in impact strength compared to the DOX/BA system. These results demonstrate that phase separation and polymer morphology in radical/cationic systems can be directed using multi-functional monomers enabling enhancements in mechanical properties including tensile toughness and impact strength. [Display omitted] •Phase separation is induced for hybrid radical/cationic formulations during photopolymerization.•Incorporation of multifunctional monomers into the DOX/BA system leads to changes in crosslinking processes.•The interplay between polymer gelation and phase separation onset determines polymer nano/microstructure.•Addition of small amounts of crosslinkers results in important changes in tan(δ) behavior of DOX/BA systems.•Significantly enhanced tensile toughness and impact strength are observed by adding appropriate crosslinker concen