| Abstract: | An attempt has been made to investigate the influence of mixed soft segment on structure and mass transfer properties of segmented polyurethane (SPU). For this purpose polyurethane block copolymer containing soft segment such as polycaprolactone glycol (number‐average molecular weight 3000, PCL 3000), PCL 3000–polypropylene glycol (number‐average molecular weight 3000, PPG 3000), PCL 3000–polytetramethylene glycol (number‐average molecular weight 2900, PTMG 2900), PPG 3000–PTMG 2900, were synthesized using a two‐step or three‐step synthesis process. All the SPUs were modified with the hydrophilic segment, i.e. diol‐terminated poly(ethylene oxide) (number‐average molecular weight 3400, PEG 3400). Fourier‐transform infrared, wide‐angle X‐ray diffraction, differential scanning calorimetry, and dynamic mechanical thermal analysis were used to characterize the polyurethanes. The mass transfer properties were measured by equilibrium sorption and water vapor permeability measurements. Mixed blocks loosen the inter‐chain interaction due to phase mixing which decreases the crystallization of the soft segment in the resulting SPU. The crystallinity of mixed polyol block SPU increases when both polyols are crystallizable in the pure state. Highest loss tan δ value was observed for the sample containing PTMG 2900–PPG 3000 mixed soft segment due to their flexible and phase mixed structure which increases the chain mobility; this sample performed best among all four SPUs in equilibrium water sorption as well as water vapor permeability owing to their loose and nearly amorphous structure. Soft segment crystal melting further enhances the water vapor permeability significantly, which would make the membrane suitable for breathable textiles, packaging and medical applications. Copyright © 2006 Society of Chemical Industry |
