Vinyl-addition polynorbornenes with glycerol and diethylene glycol moieties: Synthesis and structure-property study

A set of new norbornene-type monomers containing linear and branched substituents with three C-O-C fragments was synthesized in good yields from commercially available glycerol and diethylene glycol monomethyl ether. Vinyl-addition polymerization of the synthesized monomers was systematically studied, and highly active Pd-catalysts that made it possible to reach quantitative conversions of the monomers were suggested for their polymerization. As a result, robust thin membranes were successfully prepared directly from the polymerization mixtures in the air. Gas separation performance for a wide range of gases was evaluated for the synthesized polymers, and new valuable structure-property relationships were found. More specifically, these membranes display the facilitated transport of CO2 and solubility-controlled hydrocarbon separation selectivity. The increase in the amount of C-O-C fragments in side chains enhances these effects, but only in the case of the linear structure of the substituents. If the structure of side chains becomes branched, the gas permeability is reduced, the facilitated transport of CO2 is minimized, and the polymer becomes more susceptible to plasticization by butane. The facilitated transport of CO2 is due to the specific dipole-quadrupole interaction between CO2 molecules and polymer matrix. For the studied polymers, the contribution of this specific interaction to the solubility of CO2 achieves 64 %. The significant influence of alkyl tails in side chains on gas transport properties was also observed. To achieve better gas separation performance, it is desirable to incorporate short and rigid alkyl tails. Thus, among substituents containing ether moieties, linear oligoethylene glycols with methyl tails seem to be the most promising side-chain substituents for the macromolecular design of CO2-selective polymeric membrane materials. The results obtained were considered along with NMR, TGA, DSC, DMA, and WAXD data.