Frontal Ring-Opening Metathesis Copolymerization: Deviation of Front Velocity from Mixing Rules

Frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) shows promise for rapid, energy-efficient manufacturing of high-performance polymers and composites. Copolymerization in FROMP allows for systematic modification of materials properties while retaining the benefits of the DCPD system such as low cost of the monomer and excellent mechanical properties of the resulting polymer. While the copolymerization reactivity and copolymer properties generally exhibit monotonic dependence on monomer composition as predicted by simple, empirical mixing rules, we discovered that the frontal copolymerization behavior of DCPD with a dinorbornenyl (di-NBE) cross-linker deviates significantly from that expected relationship. As the comonomer content increases, the FROMP reaction shows a nonmonotonic increase in front velocity with intermediate compositions 40% faster than either pure component. We then studied the behavior of a series of comonomers, analyzed several factors (such as thermodynamic and kinetic properties) that might influence front velocity, and found that the nonmonotonic trend mainly results from the cross-linked structure. This copolymerization system provides a promising strategy to tune materials properties (such as glass transition temperature) and simultaneously improve the efficiency in FROMP-based materials manufacturing.