Development of highly transparent cross-linked networked waterborne polyurethane films with improved mechanical strength and hydrophobicity by thiol click reaction

Conventional waterborne polyurethanes characteristically possess a linear structure, a property that invariably leads to deficiencies in both water resistance and mechanical strength. In this study, two novel functional monomer crosslinkers, eugenol-based polyol (EUMP) and bis(mercapto)fluorine-containing binary chain extender (PTFA), were synthesised through a thiol-ene click reaction. Crosslinked network waterborne polyurethane (EUMP WPU) with different dosage of crosslinking agent EUMP was prepared by self emulsification method. The test results showed that when the amount of EUMP was 4 wt%, the contact angle of EUMP-WPU reached a maximum of 85.6° and the tensile strength reached a maximum of 23.61 MPa. Therefore, the optimum amount of cross-linking agent EUMP was selected as 4 wt%, and different amounts of dimercapto fluorinated binary chain extender PTFA were introduced into the system using the thiol-isocyanate click reaction to obtain fluorinated waterborne polyurethane (EUMP-FWPU). The EUMP-FWPU samples were characterised through a series of tests and the results showed that the mechanical strength, adhesion and hydrophobicity of the latex film were significantly improved. It was observed that when the PTFA dosage was 8 wt%, the tensile strength was 30.34 MPa, and the contact angle was 117°. The film transmittance rate is above 92 %, which can be applied to mobile phone screen protector in hydrophobic and can protect the screen without affecting the sensitivity of normal operation of the mobile phone screen.