Janus polytricyclononenes with trialkoxysilyl groups containing long alkyl tails for membrane separation of hydrocarbons

Janus vinyl-addition polytricyclononenes bearing tri(n-alkoxy)silyl groups with long n-alkyl tails (C6, C8, C10) were designed and synthesized as potential membrane materials for separation of C2+ gaseous hydrocarbons. The conditions of vinyl-addition polymerization of corresponding substituted tricyclononenes with C6 and C8 n-alkyl tails were optimized for obtaining high-molecular-weight (Mw up to 106) polymers in high yields (up to 74%). The synthesized polymers were non-crystalline and rubbery. The permeability of a wide range of individual gases was studied for the synthesized polytricyclononenes. The permeability of the CH4/n-C4H10 mixture was studied for the synthesized polymers as well as the previously described analogous polymers with shorter n-alkyl tails (C3, C4). The analysis of the results obtained led to some interesting conclusions. First, among polymers with C6-8 n-alkyl tails, permanent gas permeability almost does not depend on their length, whereas hydrocarbon permeability increases. Second, the solubility-controlled hydrocarbon separation selectivity (C2/C1, C3/C1 and C4/C1) increases with the length of alkyl tails, and this tendency remains in mixed gas experiments. Third, Janus polytricyclononenes with tri(n-alkoxy)silyl groups are strongly plasticized by pure n-butane, but, in the case of the separation of a gas mixture with a low amount of n-butane, the contribution of plasticization is significantly less even at high feed stream pressure.