UV curable polyurethane dispersions from polyisocyanate and organosilane

UV curable polyurethane dispersions (UV-PUDs) have been synthesized from hexane diisocyanate (HDI) trimer and polytetramethylene ether glycol (PTMG) with different types of capping agents (2-hydroxyethylacrylate (HEA), pentaerythritol triacrylate (PETA), aminopropyl triethoxy silane (APTES)) and prepolymer chain length (M-p). The PUD cast films were tack free prior to cure and UV cure provided the film with high solvent and yellowing resistances, and high surface properties together with high mechanical strength. Regarding the effect of capping agent, PETA gave greater hardness, modulus, strength, and glass transition temperature (T-g) than HEA due to the greater crosslink density of the polymer, and smaller swelling at large M-p. Swelling was governed by the hydrophilicity at large M-p, but by the crosslink density at small M-p. As APTES partially replaces HEA gel fraction and T-g decreased due to the decreased crosslink density, whereas hardness and contact angle increased due to the filter and hydrophobic nature of the silicon compound. Notably, the thermal degradation temperature of the UV-PUD has been increased by about 30-40 degrees C with at 3% APTES. (C) 2008 Elsevier B.V. All rights reserved.