Diffusion of cyclohexane in styrene block copolymers, relationship between mass transport and viscoelastic properties

The mass transport properties of cyclohexane in different phase separated styrene blockcopolymer, namely polystyrene-block-polybutadiene-block-polystyrene [SBS], polystyrene-blockpolyisoprene- block-polystyrene [SIS] and polystyrene-block-poly(ethylene butylene)-blockpolystyrene [SEBS] were investigated. The solubility and diffusivity in films samples have been measured, as function of concentration, at 60ºC by means of sequences of differential vapor sorption experiments run in a pressure decay apparatus. The effects of both molecular architecture (linear and star-branched for SBS) and microstructure of the elastomer mid-segment (polybutadiene vs poly(ethylene butylene) and polyisoprene) were considered. The sorption results were interpreted and modeled in terms of contributions from rubbery and glassy phases. Comparison between the different data in the binary system as function of solute concentration revealed that friction factor for solute molecules in SEBS and SIS is significantly higher than in SBS. Such results were also confirmed by linear viscoelastic characterization of the different polymers that has been carried out performing small angle oscillatory shear experiments in a wide range of temperatures between the soft block Tg and room temperature. The latter experimental data were analyzed by Time-Temperature Superposition. The relaxation spectrum has been determined and the monomeric friction factor has been extracted. This value has been correlated with results from diffusion experiments leading to a substantial agreement.