Polynorbornenes bearing ether fragments in substituents: Promising membrane materials with enhanced CO2 permeability

Abstract

Polymers with rigid main chains and flexible long side substituents combine membrane properties of both glassy and rubbery polymers. Such polymers exhibit high selectivity for CO2/N2 and light hydrocarbon separations. Herein we report synthesis and gas transport properties of two sets of addition and metathesis polynorbornenes bearing flexible ether moieties as side groups. Norbornenes with one and two ether moieties per a substituent have been prepared and used as monomers. ROMP polymerization of these monomers over the 1st generation Grubbs catalyst affords high-molecular-weight products in good yields. Vinyl-addition polymerization of norbornenes with one ether moiety in a substituent also gives polymers with good film-forming properties, while the polymerization of norbornenes with cellosolve moieties (–CH2–O–CH2–CH2–O–Alk) has been a challenge and this problem has been overcome by tuning the nature of catalytic systems based on Pd–N-heterocyclic carbene complex. The obtained polymers are amorphous and show good thermal stability. Pure permeability and diffusivity of permanent gases and gaseous hydrocarbons were investigated for these polymers. Gas transport properties are considered along with the results of quantum mechanical simulations. Key parameters of the substituents for tuning gas transport properties are discussed. Polymers with cellosolve substituents demonstrate enhanced solubility-controlled permeation of CO2. The incorporation of ether moiety in side substituents also increases solubility-controlled hydrocarbon separation selectivity (up to 35 for C4/C1 pair) compared to the similar polymers with alkyl groups.