Structure and Permeability of A-B-A-Type Block Copolymer Membranes Consisting of Poly (a-amino acid) and Polysiloxane

A-B-A-type block copolymer (MSiM) membranes consisting of poly (γ-methyl L-glutamate) (PMLG, A component) and polydimethylsiloxane (PDMS, B component) have been prepared. Their structure-CO2 permeability relationships have been investigated. Phase separation between α-helical PMLG and PDMS components has occurred in MSiM membranes, at the interface between the two phases, random-coil structure was induced in the PMLG component. As a result, the sorption behavior of CO2 in MSiM membranes can be explained in terms of the additivity between the solubility of CO2 in the three phases in the membranes: two phases of PMLG (α-helix and random-coil domains) and a PDMS phase. In the PMLG rich MSiM membranes, containing greater than 70vol% PMLG component, the solubility and diffusibility of CO2 decreased with increasing random-coil content of PMLG component. On the other hand, with increasing PDMS content, the permeability of MSiM membrane significantly increased, e. g., the CO2 permeability coefficient of MSiM membrane containing 54vol% PMLG became one order larger than those of the PMLG rich MSiM membranes. Further, MSiM membranes containing greater than 70 vol% PMLG component showed relatively high values (3.5-4.4) of oxygen/nitrogen separation factors.