Synthesis and properties of waterborne polyurethane/hydroxyapatite chemical hybrids

A series of waterborne polyurethane (WPU)/hydroxyapatite (HAP) chemical hybrids were synthesized from polypropylene glycol (PPG), 4, 4'-methylenebis cyclohexyl isocyanate (H12MDI), dimethylbutanic acid (DMBA), 2-hydroxyethyl acrylate (HEA), and vinyltrimethoxysilane (VTMS) modified HAP. Interchain siloxane bridges were introduced among the VTMS modified HAPs via sol-gel reaction while vinyl groups of VTMS segments were UV cured with HEA termini of WPU to form interchain croslinkings. In this way HAP provided WPU with internal and interchain crosslinks as well as reinforcing filler to augment thermal, mechanical, and surface properties. Glass transition temperature (Tg), contact angle, hardness, water swell resistance, and tensile modulus and strength increased with HAP inclusion showing maximum at 2% beyond which the effects were less pronounced owing to the agglomeration of HAP nanoparticles in water phase.