Preparation and properties of amino-terminated anionic waterborne-polyurethane–silica hybrid materials through a sol–gel process in the absence of an external catalyst

A series of polymer–silica hybrid materials consisting of amino-terminated anionic waterborne-polyurethane (WPU) and inorganic silica particles have been prepared through a sol–gel process in the absence of an external catalyst. Typically, amino-terminated anionic WPU was first synthesized from polycaprolactone, dimethylol propionic acid, and 4,4′-methylenebis(cyclohexyl isocyanate) with specific molar ratios, followed by further reaction with triethylamine and triethylene tetramine to give as-prepared WPU. The WPU obtained was characterized by FTIR spectroscopy and gel permeation chromatography. Subsequently, a series of hybrid materials with different silica contents were prepared by performing sol–gel reactions with tetraethyl orthosilicate (TEOS) in an amino-terminated WPU matrix without the addition of an external catalyst. This was followed by examination by transmission electron microscopy and 29Si solid-state NMR. The terminated primary amine groups attached to the as-prepared WPU chains functioned as an internal base catalyst for the sol–gel process of TEOS. The effect of composition on the thermal stability, mechanical strength, surface wettability, and optical clarity of the hybrid materials was evaluated by the thermogravimetric analysis, dynamic mechanical analysis, contact angle measurement, and UV–visible transmission spectroscopy, respectively.