Gas permeability of the film of block and graft copolymers of polydimethylsiloxane and poly(gamma-benzyl L-glutamate)

A-B-A type block copolymers of poly(gamma-benzyl L-glutamate) (PBLG, A segment) and polydimethylsiloxane (PDMS, B segment) and PDMS (trunk)-PBLG (branch) graft copolymers were synthesized, and the permeation of oxygen in water and the permeation of oxygen and carbon dioxide in the dry state were investigated. The gas permeation coefficient (P) increased with increasing content of PDMS. However, PCO2/PO2 values of copolymer films were in the range 6-9, i.e. larger than 5.4 for PDMS film. The oxygen permeation in water suffered from the interfacial resistance, which was reduced by the hydrolysis of film surface. The Arrhenius plot of the gas permeation coefficient in the dry state of the block copolymer B showed a turning point at about 40 degrees C. This temperature is close to beta-peak temperature (39 degrees C) and may be ascribed to the molecular motion of the PBLG segment. Transmission electron microscopy showed that one of the block copolymer films (PDMS 46 mol%) appears to have PDMS segments dispersed in the PBLG matrix (island-in-sea structure) and one of the graft copolymer films (PDMS 58 mol%) appears to take a lamellar structure. The gas permeation across the graft copolymer film appears to occur through the continuous PDMS phase, leading to a near-negligible activation energy in this process.