Effects of hydrophilic content on properties of waterborn polyurethane

Abstract

Polyurethane dispersion containing ionic soft segments (PU-M) was synthesized by modification of the conventional method. The ionic group content was varied by changing the amount of the internal emulsifier—dimethylolpropionic acid (DMPA) from 3 to 7 wt%. Polytetramethylene ether glycol and DMPA were reacted with the first portion of the total isophorone diisocyanate (IPDI) content. Then 1,4-butane diol and the rest of IPDI were added. Finally, the resulting prepolymer was neutralized and dispersed with water. The conventional PU dispersion containing the same ionic content was also synthesized for comparison. All PU dispersions were characterized by FTIR and 1H NMR spectrometer, laser particle size distribution analyzer, differential scanning calorimeter, thermogravimetric analyzer and pencil hardness tester. At the same content of ionic groups, PU-M had smaller particle size and larger contact angle with water. It also had higher Tg and hardness than PU-C. The increase in the ionic group content also gave smaller particle size, higher Tg and higher hardness for both PU-M and PU-C.