ROMP-Derived Aerogels

Abstract

Ring-opening metathesis polymerization (ROMP) furnishes polymers with unsaturated hydrocarbon backbones. With the advent of efficient air and solvent tolerant catalysts, ROMP can work under mild conditions and is being adopted for the synthesis of functional materials, including aerogels. Ring-opening metathesis reactions proceed via the driving force provided by strain relief, and are commonly utilized with smaller strained cyclic olefins. Dicyclopentadiene and norbornene are easily available and inexpensive monomers, and most studies of ROMP-derived aerogels described in the literature to date have focused on polymers and random copolymers of these two systems. Designer ROMP-copolymer aerogels include poly(imide-norbornene) materials based on a rod-like imide-norbornene monomer, and poly(urethane-norbornene) aerogels based on three- and nine-norbornene terminated start-like and dendritic monomers, respectively. Fundamental studies have investigated the relationship between nanostructure and bulk aerogel properties, as well as the relationship of both to the configuration and molecular make-up of the polymeric backbone (cis versus trans, interchain crosslinking). Addition of hydrogen to the backbone olefins via reduction in the wet-gel state has increased stability of ROMP-derived aerogels in air. Practical applications explored to date include thermal insulation, lining of ignition targets for inertial confinement fusion, liquid hydrogen storage, selective solvent absorption, and chemoresponsive actuators.