Synthesis and CO₂ permeation properties of novel sulfonium-substituted poly(diphenylacetylene)s

Abstract

Substitution of thiourea to poly(diphenylacetylene) having 2-bromoethoxy groups (2a) gave an sulfonium-containing poly(diphenylacetylene) [3a (Br ⁻ )]. The counteranions of 3a (Br ⁻ ) could be exchanged using CF₃COOK and (CF₃SO₂)₂NLi, and the polymers 3a (TFAc ⁻ ) and 3a (Tf ₂ N ⁻ ) were obtained. Polymer 3a (Br ⁻ ) was hydrolyzed with NaOHaq to afford the polymer 4a possessing mercapto groups. The CO₂ permeability coefficients ($P_{{{\text{CO}}_{ 2} }}$) and the separation factor ($P_{{{\text{CO}}_{ 2} }} /P_{{{\text{N}}_{ 2} }}$) of 3a (Br ⁻ ) were 15 barrers and 16, respectively. The selectivity was low compared to the analogous polymer, poly(diphenylacetylene) having imidazolium salts ($P_{{{\text{CO}}_{ 2} }} /P_{{{\text{N}}_{ 2} }} = 4 4$), because 3a (Br ⁻ ) interacted strongly with CO₂, and the diffusion of CO₂ was suppressed. The $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{CO}}_{ 2} }} /P_{{{\text{N}}_{ 2} }}$ of 3a (TFAc ⁻ ) were 43 barrers and 24, respectively, and those of 3a (Tf ₂ N ⁻ ) were 52 barrers and 26, respectively. Both permeability and selectivity increased as the counteranion became bulkier. The mercapto group containing poly(diphenylacetylene) (4a) showed a relatively high CO₂ permeability ($P_{{{\text{CO}}_{ 2} }} = 1 30$ barrers).