Poly(dimethylsiloxane-urethane) membranes: Effect of hard segment in urethane on gas transport properties

Abstract

In this study, a series of PDMS-PU membranes based on PDMS soft segment and HMDI, TDI and MDI hard segments were synthesized in order to investigate the structure–gas transport relationships. The PDMS-PU membranes synthesized were characterized by DSC and SEM measurements. The restriction of chain mobility has been shown by the formation of hydrogen bonding in the soft segment and hard segment domains, resulting in the increase in density and glass-transition temperature of the soft segment. SEM analysis showed that the microphase separation involved in the PDMS-PU membranes. Gas permeation measurements were carried for O 2, N 2 and CO 2 gases by employing different pressures. The permeability of O 2 and N 2 are independent with the pressure and CO 2 shows dependency with pressure. Increase in PDMS soft segment led to increase in permeability for all the gases. This might be the phase separation involved in both hard segment and soft segment due to the difference of solubility parameter, and the dispersed PDMS phases in the membranes serve to produce a lower resistance route for diffusing molecules. The permselectivity for O 2/N 2 gas pairs of the synthesized membranes are in the range of 2.3–2.5 and for CO 2/N 2 gas pairs from 8.5 to 14.5. The gel content of the membranes was determined by using Soxhlet extraction apparatus.