Abstract: A series of waterborne polyurethane(WPU) dispersions with different molar ratio of —NCO to —OH(n(—NCO)/n(—OH)) were synthesized using tetramethyl xylene diisocyanate（TMXDI）, polyester diol and dimethylolpropionic acid as raw materials. The effect of n(—NCO)/n(—OH) on the properties of WPU was investigated. The experiment results showed that with the increase of n(—NCO)/n(—OH), the particle size increased while the particle size distribution became wider; the crystallinity, thermostability and the water resistance tend to decrease as well. When n(—NCO)/n(—OH) was 3.0, the particle size of WPU based TXMDI was fallen in the range of 10 to 30 nm, the decomposition temperature and 24 h water absorption of WPU film were 275 ℃ and below 10%, respectively.

Key words: Waterborne polyurethane, TMXDI, thermal properties, water resistance