Synthesis of nonionic polyurethanes with hydroxyl-terminated polybutadiene hydrophobic segments and their application in octadecane nanocapsules

Alkane nanocapsule is a kind of promising phase-change material. However, it is difficult to prepare alkane nanocapsule with an elastic shell by traditional method. Therefore, nonionic polyurethane with specially designed structure was synthesized. Octadecane nanocapsule prepared by this polyurethane not only had an elastic shell but also showed some good properties in other aspects. The polyurethane structure was characterized by infrared, hydrogen-1 nuclear magnetic resonance, and gel permeation chromatography. The conductivity of emulsification process was tracked. The average particle sizes of nanocapsules were measured by quasi-elastic light scattering and fell in the range of 240 to 485 nm. Octadecane nanocapsules showed a core–shell structure under transmission electron microscopy. The nanocapsule dispersions had a rather good stability under high-speed shearing and freezing–thawing tests. All of the coalescence ratios were less than 5 wt.% after testing. The fusion enthalpy of nanocapsules reached to 83 J g−1. It was found that the dried nanocapsule powder had rather good re-dispersion ability, and stable dispersions were obtained simply by agitating the powder into water. Coalescences of re-dispersed dispersions were all less than 1.8 wt.%, and their average particle sizes were in the range of 420 to 675 nm. There was almost no change in fusion enthalpy and melt temperature before and after re-dispersion, which indicated that the polyurethane shell had a good protection of octadecane from leaking out of the nanocapsule.