Exploration of the versatility of ring opening metathesis polymerization: an approach for gaining access to low density polymeric aerogels

We report the preparation of low density polymeric aerogels using the ring opening metathesis polymerization (ROMP) approach to copolymerize dicyclopentadiene (DCPD) with norbornene-based monomers (NB-R) employing a first generation Grubbs' ruthenium-based catalyst. The ROMP approach offers an attractive synthetic method that enables the fabrication of low-density (0.02–0.05 g cm−3), uniform thickness aerogel coatings on non-planar substrates. First, we explore the effect of crosslinking in the polymer backbone on the uniformity of the gel coatings formed under shear by either adding a multi-norbornene based crosslinker (NBn-R) to increase, or linear NB-R comonomers to decrease, the degree of crosslinking, respectively. We observed that adding linear monomers dramatically improved the uniformity of the gel films which we attribute to cross-linking induced changes in the rheological properties at the gel point. Second, the copolymerization of DCPD and NB-R with a different pendant group also causes a significant change in the morphology of the PDCPD-based aerogels by modifying the lengths of the strands in the fibrous polymer network. The effect of NB-R addition on the pore structure of the aerogels is discussed in the context of a molecular and interparticle crosslinking model. Finally, (bis)iodo-norbornene was synthesized to demonstrate the feasibility to fabricate functionalized aerogels by using our copolymerization approach. Our results highlight the potential of the ROMP-based copolymerization approach as a facile and versatile route to functionalized low density polymeric aerogels.