Preparation Of A Water Vapor Permeability Controllable Shape Memory Polymer And Its Application On Fabrics

The development of smart polymer is currently of great interest in the world. Intelligent water proof and moisture permeability fabric has became one of the hottest fields of this kind of materials. As one of the most promising smart material, Shape memory polyurethanes (SMPU) was investigated in this paper. Thermally sensitive poly (N-isopropylacrylainide -co-sodium acrylate) hydrogels was introduced into SMPU, because of its sharp phase transition in volume around its LCST. By such design, the mixed polymer film is given higher vapor permeability at warm temperatures and lower permeability at coldness compare to shape memory polyurethane film, which made a highly promising future for intelligent breathable textiles.SMPUs were tailor made in order to obtain the phase transition temperature (soft segment crystal melting temperature) in the room temperature range, and were prepared by solution polymerization. The SMPUs were characterized using differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The DSC results indicated that SMPUs had descending phase transition temperature (soft segment crystal melting point, T_s,m) with the hard segment content increasing and the molecular weight of soft segment decreasing. The phase separation of SMPU increased with the decrease of hard segment content as well as with the increase of the molecular weight of soft segment, which proved by the WAXD measurements. Temperature-sensitive water vapor permeability of SMPU at the phase transition temperature was observed, which was changed obviously with different SMPU hard segment content.Hydrogels were prepared by free radical polymerization in aqueous solution of N-isopropylacrylamide (NiPAAm) with sodium acrylate (SA) as comonomer in order to get a thermo- & pH-sensitive hydrogels with goods welling property. Hydrogels prepared with different comonomer concentrations, dosage of cross-linker and under different synthesis temperatures were investigated in this paper. The resulting hydrogels synthesized at 35℃, using 2% crosslinking agent, and copolymer ratio(SA/NiPAAm) of 98/2, exhibited a fast thermo-responsibility, good swelling ability.The mixed polymer film of SMPU and dispersed gel particles were prepared by mechanical blend. It gives a better water vapor permeability compare to SMPU films, and the water vapor permeability volume increased with the increase of PNiPAAm-co-SA hydrogel content.