Synthesis and gas permeability of methylol-group-containing Poly(diphenylacetylene)s with high CO2 permeability and permselectivity

Abstract

Diphenylacetylene monomers bearing a methylol group protected by a t-butyldiphenylsilyl group [tBuPh2SiOCH2C6H4CCC6H4R; R = SiMe3 (1a) and R = SiMe2nC18H37 (1b)] were synthesized and then polymerized with TaCl5/n-Bu4Sn to afford the corresponding poly(diphenylacetylene)s 2a and 2b, respectively. The molecular weights of 2a and 2b were high (i.e., Mw = 1,020,000 and 1,560,000, respectively), and free-standing membranes were obtained by solution casting. The deprotection of membranes of 2a and 2b using n-Bu4N+F− afforded poly(diphenylacetylene)s bearing methylol and silyl groups (3a and 3b). On the other hand, treatment of membranes of 2a and 2b with trifluoroacetic acid led to deprotection and desilylation, producing poly(diphenylacetylene)s bearing trifluoroacetate moieties (4a and 4b, respectively), and then treatment with methanol afforded poly(diphenylacetylene)s bearing only methylol groups (5a and 5b). The carbon dioxide permeability coefficients (PCO2) of membranes of 2a and 2b were 99 and 78 Barrer, respectively. Deprotection led to the increment of CO2 permeability without the decline of the CO2 permselectivity. Poly(diphenylacetylene)s bearing methylol and silyl groups (3a and 3b) exhibited high permeability (PCO2 = 2000 and 120 Barrer, respectively), but not high permselectivity (PCO2/PN2 = 17 and 16, respectively). Methylol-group-containing poly(diphenylacetylene) without silyl groups 5b exhibited the best CO2 permeation property, i.e., high CO2 permeability and high permselectivity (PCO2 = 220 Barrer, PCO2/PN2 = 32).