In order to further reduce the water content in the UV-curable aqueous oligomers

the water-diluted polyurethane acrylate (WPUA) oligomer was synthesized using toluene diisocyanate as hard segment

polyether polyol and polyethyleneglycol as soft segments

dimethylol propionic acid (DMPA) as hydrophilic reactant

hydroxyl propyl acrylate and pentaerythritol triacrylate as end-capping reagent

and triethylamine as neutralizer. The solid contents of the oligomer were about 80%. The influence of types and molecular weight of soft segments

the molar ratio of -NCO/-OH

the addition sequence and amount of DMPA

and the amount of inner crosslinking agent and COOH on the viscosity and film properties of UV-curable oligomer was investigated. The prepared products were characterized by UV curing

tensile strength tests

FTIR

GPC and other analysis. The results showed that the COOH content was not only the factor influencing the viscosity of the oligomer. The diols of small molecular weight

the value of n(-NCO):n(-OH) between 1.7 and 1.8

DMPA concentration in hard segments or soft segments

and 15% of trimethylolpropane were more favorable to reduced viscosity. An optimum synthesis result was obtained when the pencil hardness was H

the bending flexibility was 2 mm

the fastest curing time was 2 s

the largest tensile strength was 11.88 MPa

and the largest elongation was 21.4%. More than 60% of water content was reduced by the waterborne UV-curable coatings as compared with similar products sold in the market. Thus

this UV-curable WPUA can be apply to reduce both the humidity and time requirements.