Microporosity of Polynorbornenes by Positron Annihilation and Sorption Data

Abstract

Based on positron annihilation and low-temperature gas (CO2) sorption data, we discuss the nature of size distribution of micropores in a number of polynorbornenes with various substituent groups in the side chain. The local stiffness of highly permeable glassy polymers suggests that they are microheterogeneous. In this case, distributions that are bimodal in nature seem quite possible, although unimodal cases cannot be excluded either. The positron annihilation data are consistent with these concepts and correlate with permeability. At the same time, the positron and sorption data on porosity are found to have discrepancies, which are explained either by limited mobility of the positronium atom or by inaccuracy of description of the sorption curve according to the density functional theory (NLDFT) and the Monte Carlo method (GCMC).