Reversible transformations in bulk polymers offer numerous possibilities for materials remodeling and reprocessing. While reversible systems based on dynamic covalent chemistry such as the Diels–Alder reaction and transesterification have been intensively studied to enable local bond dissociation and formation, reports regarding the reversion from bulk network polymers to monomers are rare. Herein, we report a reversibly polymerizable system based on ring-opening metathesis polymerization of cyclopentene derivatives in the bulk state. The network polymer is thermodynamically stable and mechanically robust at room temperature and readily depolymerizes at elevated temperatures to yield liquid monomers that are repolymerized to cross-linked polymers by simply cooling to room temperature. This reversible process was characterized by differential scanning calorimetry and rheological tests.

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 crosslinked 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.