Synthesis of poly(diphenylacetylene)s with high gas permeability incorporating fluorine, chlorine, and methyl groups: Influence of the substitution position of fluorine and chlorine atoms on gas permeability

Highly gas-permeable polymers represent promising candidates for gas separation membranes. In prior research, we developed gas-permeable poly(diphenylacetylene) derivatives incorporating both trimethylsilyl and methyl groups. In the present study, we synthesized novel gas-permeable poly(diphenylacetylene)s that include halogen atoms, such as fluorine and chlorine, in addition to trimethylsilyl and methyl groups. Notably, high gas permeability (oxygen permeability coefficients exceeding 5,000 Barrer) was observed in poly(diphenylacetylene)s containing fluorine atoms at the para -position of benzene rings. Conversely, analogous poly(diphenylacetylene)s with chlorine atoms at the para -position exhibited lower gas permeability, with oxygen permeability coefficients around 2,000 Barrer. X-ray diffraction analyses revealed that the distances between main chains in polymers with chlorine atoms at the para -position were greater than those in polymers with fluorine atoms at the same position. These findings suggest that the larger size of chlorine atoms significantly occupies the free volume space. Furthermore, the desilylation of these poly(diphenylacetylene)s with halogen atoms at the para -position resulted in increased gas permeability. The presence of halogen atoms at the para -position of benzene rings appears to suppress polymer chain packing through the desilylation reaction. • Poly(diphenylacetylene)s with trimethylsilyl, methyl, halogen are synthesized. • Diphenylacetylene with chlorine at ortho -position do not undergo polymerization. • Substituents at para -position significantly affect the gas permeability. • Incorporation of fluorine at para -position effectively enhances permeability.