Influences of van der waals volume of substitute groups on CO 2 permselectivity of polyimide‐A molecular simulation study

Polyimide (PI) as a typical glassy polymer material was investigated by molecular simulation to reveal the relationship between polymer molecular structure and its gas separation properties. The influences of van der waals volume ( V w ) on CO 2 permselectivity of PI polymers (with four kinds of backbone substitute groups and a series of side substitute groups from small to large volume) and V w was proposed as an intermediate to establish the relationship between the substitute group and permselectivity. The results show that the CO 2 permeability ( P ) simply increases and CO 2 /N 2 selectivity ( S ) decreases with the increasing V w of side substitute groups. The linear fitline of P‐V w is much suitable to describe and predict the effect of the increasing V w of side substitute group on improving permeability by analyzing the experimental and calculated CO 2 permeability. The increasing V w of backbone substitute group can slow down the increasing of CO 2 permeability, but result in the decreasing first and then recovering to the original level. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131 , 41082.