In order to achieve fabrics with both good warmth retention at low temperature and fine sweat volatility at high temperature

a novel semi-interpenetrating polymer network (semi-IPN) based on polyurethane (PU) and poly(N-isopropylacrylamide) (PNIPAM) was synthesized via the strategy of in situ crosslinking polymerization

and the semi-IPNs were fabricated into microporous membranes by immersion precipitation phase inversion method.The relationship of the morphology and porosity of the membranes with the chemical structure of the semi-IPNs and fabrication parameters of membranes was investigated.The hydrophilicity

swelling properties and water vapor permeability of the membranes at various temperatures were then evaluated and compared.Generally

the water contact angle decreases with the introduction of PNIPAM content in the semi-IPN.Therefore

the PU/PNIPAM semi-IPN membranes have better hydrophilicity than the membranes prepared from pure PU.On the other hand

the surface hydrophilicity of the semi-IPN membranes is inhibited at high temperatures.The temperature-sensitivity was also found in the swelling properties of the semi-IPN membranes.The equilibrium swelling ratio (ESR) of PU membrane increases slightly with temperature.But with the increase of PNIPAM content

the membrane ESR decreases significantly with temperature

revealing the obvious volume contraction of the semi-IPN material at high temperatures

which is endowed by the hydrophilic-hydrophobic transition of PNIPAM with temperature.The pore diameter of the semi-IPN membranes is therefore enlarged.The enlargement could be confirmed by the results in water vapor permeability (WVP).The WVP of PU membrane at 50℃ is about 2 times of that at 25℃

which is caused by the enhancement of vaporization rate and molecular mobility of water vapor.In contrast

the WVP of semi-IPN membranes at 50℃ can reach more than 4 times of that at 25℃.These results prove that by the method proposed in this paper

membranes with fine temperature-sensitivity and high water vapor permeability can be prepared

and such membranes are highly valuable in the applications of intelligent garments.