Fabrication and characterization of novel polyurethane Encapsulant with excellent underwater acoustic transparency and hydrophobicity

The preparation of underwater acoustically transparent polyurethane with excellent acoustic transparency, hydrophobicity, and electrical insulation is the current bottleneck prior in the underwater acoustic system. In this work, we synthesized a series of acoustically transparent polybutadiene-based polyurethane (FPU) modified with a,ω-dihydroxypoly[(3,3,3-trifluoropropyl)methylsiloxane] (PTFPMS) by prepolymerization method. The influence of the PTFPMS content on the hydrophobicity, acoustic transparency, electrical insulation, and mechanical properties of FPU were investigated. When the amount of PTFPMS was 10 wt%, the water absorption of FPU reached the minimum of 0.261%, which was 42.9% lower than that of neat polyurethane. Moreover, the acoustic impedance of FPU decreased to 1.584 × 10 5 g/cm 2 ∙s, which was very close to that of seawater and indicated a favorable acoustic transparency. In addition, the volume resistivity and surface resistivity of FPU were 5.20 × 10 14 Ω cm and 2.42 × 10 14 Ω cm, respectively, suggesting an excellent electrical insulation. These results revealed that the as-prepared FPU has promising applications in the fields of underwater acoustically transparent encapsulant.