Effective increase in permeability and free volume of PIM copolymers containing ethanoanthracene unit and comparison between the alternating and random copolymers

To investigate possible effects of monomer's sequence distribution along the chain of polymers of intrinsic microporosity the two model PIM copolymers having well-defined alternating fashion (A1) and statistically random distributed fashion (S1), respectively, were prepared. A detailed determination of gas permeation parameters was performed and free volume via positron annihilation lifetime spectroscopy was studied for these materials. Investigation of their gas permeability showed that the alternating copolymer A1 revealed somewhat higher permselectivity and lower permeability coefficients than those of the random copolymer S1. Both copolymers are significantly more permeable than the original PIM-1 due to the inclusion of ethanoanthracene co-monomer. The treatment with ethanol results in increases in gas permeability as is the case for many highly permeable glassy polymers. Higher gas permeability of S1 can be explained by larger free volume as estimated via positron annihilation lifetime spectroscopy.