Effects of Heterogeneous Linear Polyether Segments on the Membrane Breathability of Nonionic Polyurethane

Characterizing the relationships between the water repellency and moisture permeability (breathability) of hydrophilic polyurethane and its supramolecular structure, including the phase inversion temperature in the soft phase, is unavoidable when developing intelligent, breathable textile products. In this study, a two-step technique was employed to prepare hydrophilic nonionic polyurethanes (PU) with various polyether (PE) soft segments. The hard segments of the samples were composed of 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO), while the soft segments consisted of polyethylene glycol 1000 (PEG), polytetramethylene glycol 1000 (PTMG), or their mixture. The relationships between the chemical and physical structure and the breathability were studied. The results showed that the samples with better separated structure between the soft and hard domains had a special microstructure of partial compatibility and simultaneously partial separation between the polyether soft and hard domains. In addition, the distribution of the mixed polyethers in the soft domains was homogeneous. The microphase structure, especially the hydrophilic ether bond content, exhibited a specific corresponding relevancy to the water resistance, moisture permeability and hydrophilicity of the PU membrane. The moisture permeability and water resistance were also directly related to their film-forming properties. Enhanced microphase separation intensified the positive effects of ether bonds on the moisture permeability, while worsened microphase separation weakened their negative influence on the water resistance/hydrophobicity.