Gas and water vapor sorption and diffusion in a triptycene-based polybenzoxazole: effect of temperature and pressure and predicting of mixed gas sorption.

Abstract Fundamental gas transport properties of a novel thermally rearranged polymer (TPBO) prepared from a co-polyimide precursor with controlled triptycene molar content are discussed. He, N 2 , CH 4 , CO 2 and C 2 H 6 sorption isotherms were experimentally measured in the range 5–50 °C and up to 32 atm and analyzed with the dual mode model. Water vapor sorption and diffusion at 35 °C was also investigated. TPBO exhibits larger gas and vapor sorption capacity relative to previously reported thermally rearranged polymers. The dual mode parameters retrieved from the analysis of single gas sorption isotherms were used to estimate a priori the sorption behavior in mixed gas conditions. The predicted mixed gas solubility-selectivity is significantly higher than ideal solubility-selectivity and it is comparable to that exhibited by other glassy polymers. Gas and vapor diffusion coefficients in TPBO were estimated from the solution-diffusion model and from sorption kinetics, respectively, and are larger than in previously reported thermally rearranged polymers. The dual sorption-mobility model indicates that the polymer rigidity significantly affects gas diffusion coefficients. CO 2 /CH 4 diffusivity-selectivity was larger than in other glassy polymers, pointing out the superior size-sieving ability provided by triptycene units. Water vapor sorption experiments revealed that TPBO is more hydrophilic relative to previously reported thermally rearranged polymers: theoretical models were exploited to speculate water vapor distribution in the polymer matrix. Graphical abstract fx1 Highlights • Gas solubility in TPBO is larger relative to other high performance polymers, except PIM-1. • TPBO exhibits larger diffusivity-selectivity relative to other polymers. • TPBO is more hydrophilic relative to previously reported TR polymers. • Polymer rigidity affects gas diffusion behavior. [ABSTRACT FROM AUTHOR]