Novel waterborne UV-crosslinkable thiol-ene polyurethane dispersions: Synthesis and film formation

A new class of water-dispersible polyurethane pre-polymers bearing pendant unsaturation was synthesized and used with polyfunctional thiol crosslinkers to prepare uniform aqueous colloidal dispersions capable of forming crosslinked films upon UV exposure at 254 nm. This novel approach to prepare UV crosslinkable, water-based polyurethane polymers offers numerous advantages over other similar systems. Photocuring behavior of films from such thiol-ene polyurethane dispersions (TE-PUD) was monitored using ATR-FTIR spectroscopy by following consumption of thiol and ene functionalities as a function of UV exposure time. Dynamic mechanical analysis (DMA) revealed a decrease of the glass transition temperature (Tg) with increasing thiol/ene ratios ranging from 0.5 to 1.1.