Synthesis And Properties Of Hyperbranched Polymer Based Waterborne Polyurethane Emulsion

Because of using dimethylol propionic acid as cross-linking agent, the polymer dispersions is linear and the water-resistant of the film is poor. At present, enhancing cross-linking degree is the measure that is most studied, relatively effective and easy to implement. Therefore, in order to enhance the water-resistant, the hyperbranched polymer is introduced into the polyurethane.In this paper, hyperbranched polyester Boltorn H20 was first modified by maleic anhydride. Then the modified H20 was added to the reaction system of polytetrahydrofuran glycol 2000 and 5-isocyanato-1-(isocyanatomethyl)-1,3,3-tri-methylcyclohexane. Triethylamine was added as neutralizer. The stable emulsion of hyperbranched waterborne polyurethane was prepared under high-speed stirring.The results showed that, the reaction time of modification of H20 by succinic anhydride in acetone was longer than in 1,4-dioxane. The reaction time was also different for different derivative degree of H20 hydroxyl group. FTIR and NMR showed that H20 had been successfully introduced the carboxyl-terminated group.The influence of molar ratio NCO/OH (5:1 and 2:1) was discussed. The result showed that the molar ratio had little impact on the rate change of NCO%. Temperature and the catalyst had relatively large impact on the rate change of NCO%. The higher the temperature was, the faster polymerization rate was. A small amount of dibutyl tin dilaurate could accelerate the decrease of NCO% significantly. After several tests, the best pre-polymerization condition was without any catalyst,80℃, initial molar ratio 2:1 for 4h. After that, the pre-polymer was crosslinked by H20-2MA in 7h detected by FTIR.Carboxyl content, polyether diol, neutralization degree, emulsification conditions and other factors will affect the particle size and storage stability of hyperbranched polyurethane emulsion. The stable emulsion could be obtained with carboxyl content 2.05%. The stable and milky emulsion was obtained using PTHF2000 as diol instead of PEG2000. When the neutralization degree was 0.7-1.0, the emulsion was stable, and the particle size was smaller. The result also showed that the neutralization temperature should be not higher than 35℃to prepare stable emulsion. When the temperature was too low, it was difficult to prepared emulsion. The best condition to prepare a stable emulsion was with carboxyl content 2.05%, PTHF2000 as polyether diol, and neutralization degree 1.0, emulsified at 30-35℃. The prepared hyperbranched waterborne polyurethane emulsion had the particle size of 0.082 um, and was stable for 6 months or more. The initial thermal decomposition temperature of polyurethane film was 260℃, and water absorption was 7.14%. Compared with other literatures, the water resistance and thermal stability of hyperbranched waterborne polyurethane film was enhanced.