Structure of the Thermally Induced Cross-Link in C-Linked Methyl Ester-Functionalized Polydicyclopentadiene (fPDCPD)

Abstract

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.

Harnessing the surface chemistry of methyl ester functionalized polydicyclopentadiene and exploring surface bioactivity

“…In our previous mechanistic studies, 19 we confirmed that the principal crosslinking mechanism for 2 does not take place via secondary metathesis events of the type that are generally considered for unfunctionalized polydicyclopentadiene [49][50][51][52][53] but rather through a self-initiated, head-tail radical polymerization event that occurs through the methacrylate motif embedded within 2 (Scheme 1a). In order to achieve robust attachment of f PDCPD to glass slides, we further exploited this mechanism by carrying out the thermal curing event on the 3-(trimethoxy silyl)propyl methacrylate-coated slide, with the goal of engaging the methacrylate groups in the surface-activating reagent directly in the self-initiated radical polymerization event that occurs across the methacrylate groups in linear polymer 2, resulting in the formation of strong covalent bonds that serve to link the f PDCPD polymer to the glass slide.…”

“…Understanding the chemical properties of a novel material is paramount to discovering its possible future applications. Although some of the unique properties of f PDCPD have been reported previously by our group, [18][19][20] the degree to which the surface can be further functionalized is not yet completely understood. For example, while previous work has shown that partial hydrolysis of the ester functional groups on the surface of f PDCPD can raise the surface energy, 18 we have not yet examined the installation of other functionality at this position.…”

“…In retrospect, this is not surprising; we previously showed that crosslinking density in f PDCPD can be controlled with heating time. 19 More densely crosslinked samples are presumably less able to swell when exposed to TBO in solvent, which results in a lower uptake of the reagent.…”

“…21 f PDCPD offers a tunable, elevated surface energy, and a higher T g compared with the parent material. 18 Importantly, both the thermal stability of f PDCPD (as assessed by thermogravimetric analysis) 18,19 and the storage modulus (measured by dynamic mechanical analysis) 20 were shown to be similar to those of the parent polymer. The introduction of new functionality while maintaining durability allows for further modifications, potentially increasing the applications of f PDCPD for industrial and biomedical use.…”

“…17 To address the low surface energy of PDCPD, and to bestow additional function to the polymer, we installed a C-linked ester group on the dicyclopentadiene monomer. [18][19][20] The esterfunctionalized monomer ( f DCPD) engages in Ru-catalyzed ROMP similarly to the parent dicyclopentadiene, to afford a linear telechelic polymer that can then be thermally cured to provide a densely crosslinked, functionalized form of polydicyclopentadiene that we call f PDCPD (Fig. 1).…”