The effect of poly(alkyl (meth)acrylate) segments on the thermodynamic properties, morphology and gas permeation properties of poly(alkyl (meth)acrylate)-b-poly(dimethyl siloxane) triblock copolymer membranes

Abstract

The structure-property relationship of the poly(alkyl (meth)acrylate)-b-poly(dimethyl siloxane) (PA-b-PDMS) triblock copolymers were studied for membrane application. The effect of PA segments with different main-chain flexibility and side chains such as poly(benzyl methacrylate) (PBzMA), poly(ethyl methacrylate) (PEMA) and poly(methyl acrylate) (PMA) were studied on the properties of PA-b-PDMS block copolymer membranes. The block copolymers were synthesized via atom transfer radical polymerization (ATRP). The morphology structure of the synthesized block copolymers was changed from spherical to the cylindrical type by changing the structural segments from PMA and P(EMA-b-PEMA) to PEMA, respectively. The morphological feature of the PA-b-PDMS block copolymers was discussed according to their thermodynamic properties (surface energy, the solubility parameter of the constituent segments, and binary interaction parameters). The glass transition temperature of the hard segments of PA-b-PDMS block copolymers was increased by increasing poly(alkyl methacrylate) segments. CO2 permeability of the P(EMA-co-MA)-b-PDMS-b-P(EMA-co-MA) block copolymers was increased (from 7.2 Barrer to 908 Barrer) by increasing MA repeating units which correlated to the higher main chain flexibility of MA compared to the EMA repeating units. Permeability of CO2 was increased 27% by substitution of BzMA repeating units of P(BzMA-co-MA)-b-PDMS-b-P(BzMA-co-MA) block copolymer with EMA and correlated with the lower fractional free volume of BzMA repeating units.