The varying mass ratios of soft and hard segments in waterborne polyurethane films: Performances of thermal conductivity and adhesive properties

Waterborne polyurethanes (WPUs) with different mass ratios of soft and hard segments were synthesized by toluene diisocyanate, polypropylene glycol (PPG) and ethylene glycol (EG). It was shown that the PPG-based WPU with a mass ratio of soft and hard segments of 3:2 expressed a highest thermal conductivity (similar to 0.374 W/m.K), but showed a lowest T-peel strength (21.55 N/25 mm). As the mass ratio of soft and hard segments increased to 4:1, the T-peel strength was increased to 136.14 N/25 mm and thermal conductivity was decreased to a lowest value (similar to 0.306 W/m.K). To gain more understandings a number of analytic were carried out, such as FTIR, TG, DSC, DMA, AFM and XRD. Furthermore, mechanical properties of the PPG-based WPU coatings were tested as well. A possible explanation for the change in properties is due to the degree of phase separation and crystallinity, which was increased with the increasing of hard segment content. As a result, the hard and soft segments formed orderly oriented stacked structures by owing to the increasing of phase separation.