Preparation and assistant-film-forming performance of aqueous polyurethane dispersions

A series of novel trimethylol propane monoesters were synthesized to prepare aqueous polyurethane dispersions (PUD), which were used as a polymer coalescent to assist the film forming of high Tg polyacrylate latexes (PA). The effects of trimethylol propane monoester categories, NCO/OH molar ratios, soft segment contents, dimethylolpropionic acid (DMPA) contents, and diamine chain extenders on assistant-film-forming performance of PUD were investigated. The surface microstructures of PA/PUD blend latexes were also characterized with scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results showed that the PUD prepared from trimethylol propane monolaurare (TMPLA) with long-chain alkyl groups displayed excellent assistant-film-forming ability. The assistant-film-forming ability of PUD was increased with decreasing of NCO/OH molar ratios and hard segment proportions. The optimum preparation process of better assistant-film-forming PUD was that isophorone diisocyanate (IPDI), polyether 220 (N220), trimethylol propane monoester (TMPLA) and adipic acid dihydrazide (ADH) as reactants, 1.5 of the NCO/OH molar ratios, 55/45 of the soft/hard segment mass ratio and 5% of ω (DMPA). The high Tg polyacrylate latexes with PUD could form a continuous transparent film at 5 °C with 30 g L−1 of the volatile organic compounds (VOC) contents and display good film performance.