A series of polyurethane aqueous dispersions

which were prepared from raw materials of toluene diisocyanate (TDI)

polypropylene glycol (PPG)

and dimethylol propionic acid (DMPA)

were used to study post-chain extension process with ethylene diamine (EDA) as chain extender

including factors of H2O

temperature of post-chain extension

molar ratio of -NCO/-OH in raw materials

and chain extension ratio. FT-IR results showed that the post-chain extension process of polyurethanes with EDA was affected by H2O in aqueous dispersion through competitive reactions of H2O with residual -NCO groups in polyurethane chains. Measurement of molecular weight

particle diameter

and zeta potential of polyurethane dispersions before and after chain extension indicated that chain extension by H2O resulted in instability of polyurethane dispersions. The influence of H2O on EDA post-chain extension process was significant at low chain extension ratio

whereas molecular weight of chain-extended polyurethanes was lowered at high chain extension ratio. When chain extension temperature was increased

molecular weight of EDA chain-extended polyurethanes was decreased

but diameters of polyurethane dispersions were increased. With molar ratio of -NCO/-OH in raw materials at 1.20

chain extension temperature at 30℃

and chain extension ratio at 60%

the H2O impact on post-chain extension of polyurethanes with EDA was reduced effectively.