In the United States, separation processes consume 16 quadrillion BTUs of energy annually, accounting for approximately 50% of the total annual energy consumed by the entire chemicals industry. About 53% of the energy used for separation processes is expended by distillation, requiring significant energy input to overcome heats of vaporization. If distillation were replaced with membrane-based separations, a projected 90% of energy losses could be saved. Industries today have adopted membranes made of polymers like cellulose acetate to perform separations, but limitations such as instability in aggressive environments and suboptimal performance prevent a broader adoption of membrane technologies. Over the past 15 years, a sizable interest in polymers of intrinsic microporosity (PIMs) developed. PIMs, which are synthesized through step-growth polymerization, are the first class of processable ladder polymers applied to gas separations. They feature rigid backbones with kinks that inhibit dense packing of polymer chains, resulting in higher permeability compared to current commercial membranes. However, PIM-1 shows undesirable instability against physical aging and plasticizing gases—phenomena indicative of poor real-world performance. To address these limitations, microporous polymers featuring rigid, pore-generating side chains on flexible backbones were synthesized through a novel reaction based on Ring Opening Metathesis Polymerization (ROMP). Macro-monomers formed by Diels-Alder reactions are converted into high molecular weight polymer with low polydispersity by ROMP. The method enables variability with pendant groups besides the more traditional post-polymerization modification routes. As a result, fluorinated moieties were introduced on the polymer structure, enhancing gas transport properties with record-breaking permeability for CO2, ideal for carbon capture applications. ROMP polymers further displayed reduced physical aging and unprecedented plasticization resistance.

Side chain rigidity and backbone flexibility: Poly(Ladder) ROMPs for gas separations

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.