Gas sorption and diffusion in hydrogen‐bonded polymers. I. Vinyl alcohol/vinyl butyral copolymers

A series of vinyl alcohol/vinyl butyral copolymers was examined to assess the effect of internal hydrogen bonding on gas sorption and diffusion. Sorption and permeation measurements for carbon dioxide and methane were performed on four vinyl alcohol/vinyl butyral copolymers. Upon comparing the various data, it was found that hydrogen‐bonded copolymers exhibit a much wider variation in diffusion coefficient than non‐hydrogen‐bonded copolymers. The fractional free volumes of the studied copolymers were considerably lower than expected based on values of the diffusion coefficient. This may be due to the fact that predicted occupied volumes are too large and that the effect of internal hydrogen bonding is not accounted for properly. Using a relationship between infrared spectral shift and hydrogen‐bond length, fractional free volumes in the hydrogen bonded copolymers were correlated with the interatomic spacing associated with the hydrogen bond. This implies that the average length of a hydrogen bond can be used as a measure of chain packing in hydrogen‐bonded polymers.