Structural characterization and mass transfer properties of nonporous segmented polyurethane membrane: Influence of hydrophilic and carboxylic group

An attempt has been made to investigate the influence of hydrophilic and carboxylic groups on structure and mass transfer properties of polypropylene glycol (number average molecular weight of 1000 g mol−1, PPG 1000) based segmented polyurethane (SPU). Polyethylene glycol (number average molecular weight of 3400 g mol−1, PEG 3400) (hydrophilic segment) or dimethylol propionic acid (DMPA) (carboxylic group) or combination of PEG 3400 and DMPA were used to modify the SPU. For comparison, SPU without hydrophilic/carboxylic group was also synthesized. Structures were investigated by Fourier-transform infrared (FT-IR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and tensile tester. Mass transfer properties were investigated by equilibrium sorption and water vapor permeability measurements. FT-IR spectra of CO stretching was indicated that with the introduction of hydrophilic or acid groups in the polymer backbone, the hydrogen bonding of urethane groups were became weaker or stronger respectively. Nearly amorphous structures of all SPU samples were evidenced by WAXD and DSC results. The presence of DMPA increases the interaction between the polymer chains, which increases the glass transition temperature (Tg) and make the polymer tough. In contrast flexible PEG 3400 segment decreases the Tg and increases the percent strain at maximum load. Experimental results revealed that the mass transfer properties not only influenced by amorphous region but also on the interaction between the polymer chains. Presence of hydrophilic group enhances the sorption as well as water vapor permeability (WVP). Abrupt changes of mass transfer properties were observed for SPU with PEG 3400 due the presence of more polar group and longer flexible chains of PEG 3400 which will originates holes in the polymer membranes. The membrane with DMPA content, lowest permeabilities was characterized by a higher degree of physical cross-linking imposed by carboxylic functionality.