Polydicyclopentadiene (PDCPD) is a durable, highly cross-linked material that is used industrially for the production of automotive body panels among other applications. We recently described a novel C-linked, ester-functionalized polydicyclopentadiene (fPDCPD) that introduces a tunable surface energy and increased T-g, without sacrificing the desirable thermal stability of the parent polymer. In this report, we describe an extensive spectroscopic study aimed at the rigorous characterization of the structure of the cross-link in our thermally cured material. The results from this study rule out the involvement of metathesis-derived interchain couplings and show that the majority of cross-links derive from thermally initiated radical polymerization of the embedded methyl methacrylate motif We also show that the degree of cross-linking can be tuned by the applied thermal conditions; rapid high-temperature heating freezes the system at a relatively low cross-link density, while longer heating at a lower temperature allows cross-linking to proceed nearly to completion.