Synthesis of aqueous and hydroxy-terminated polyurethanes: Impacts of formulation parameters by orthogonal matrix design

Traditional hydroxy-functional aqueous polyurethanes have most commonly two hydroxyl groups per molecule in currently available aqueous polyurethanes. In this study, target product is polyhydroxyl-terminated polyurethane, which has the following advantages: (1) the number of hydroxyl groups: Target product=3×Tradition product. (2) Dispersibility in water of dispersion: Target product≫Tradition product. (3) Degree of crosslinking, air-drying property and mechanical properties of two-component PU film: Target product>Tradition product. •Aqueous and hydroxy-terminated polyurethanes (AHPUs) were synthesized.•L16(45) orthogonal matrix design was used to optimize synthesis condition of AHPUs.•The synthetic AHPUs have good physical properties such as relative viscosity.•The two-component films have good properties under the optimum synthesis condition. Aqueous and hydroxy-terminated polyurethanes (AHPUs) were synthesized using poly(caprolactone) glycol, isophorone diisocyanate, dimethylolpropionic acid (DMPA) as main raw materials, trimethylolpropane (TMP) as crosslinking agent, ethylenediamine (EDA) as chain extender, and tris(hydroxylmethyl) aminomethane as chain terminator. The optimum synthesis condition of AHPUs was elected by L16(45) orthogonal experiments with the content of DMPA (A) and TMP (B), molar ratio of isocyanate to hydroxyl in the prepolymerization step (C) and the molar ratio of amino groups in EDA to residual isocyanate groups of prepolymerization (D) as factors and the transmittance, relative viscosity and particle size of dispersions as evaluation index, and the tack-free drying time, gloss, hardness, adhesion and water resistance of coatings were discussed, too. The results demonstrate that the synthetic AHPUs have good physical properties, such as relative viscosity, transmittance and particle size, what's more, the two-component films have good air-drying ability, gloss, hardness, adhesion and water resistance when synthesis parameters are A=7.0wt%, B=5.0wt%, C=1.6 and D=0.2.