Study On Structure And Properties Of Waterborne Polyurethanes

The preparation of waterborne polyurethanes was main line in this paper. It was discussed respectively including prepolymer reaction kinetics,influence factors of polyurethane prepolymer viscosity and mechanical property of the film.The reaction kinetic between diphenyl-methane-diisocyanate and polypropylene glycol,dicyclohexylmethylmethane-diisocyanate and polyester were investigated in this paper with IR online monitor system,IR React^TM 4000.The IR absorption peak development of isocyanate and urethane in the reaction process was studied.The reaction kinetics of the isocyanate with the hydroxy group was analysised systematically by these IR spectrum Figure,the reaction kinetics constants of 4-NCO and 2-NCO in MDI monomer k=2.833×10⁴exp(-47862/RT)(L.mol^-1.min^-1 ),k=6.725×10⁹exp(-88078/RT) (L.mol^-1.min^-1),H₁₂MDI in the system without catalyst and in the system with catalyst k=0.5exp(-15652/RT),k=0.285exp(-6481/RT) were obtained.The preparation of polyurethane prepolymer was based on MDI-50 and three kinds of polyol,including prepolymer number average molecular weight, the content of the highest molecular weight,the content of hard segment, unsaturation degree of polyether terminal group,etc.The prepolymer viscosity was controlled by prepolymer number average molecular weight,the content of the highest molecular weight and the content of hard segment.As Mn>Mc,the content of the highest molecular weight played a leading role.As Mn-1 from the experimental data.The prepolymer viscosity was influenced by strongly polar hydrogen bond and oligomer molecular chain conformation which were formed by hard segment and the effect was always existed.Different formula waterborne polyurethanes were prepared by H₁₂MDI and polyol.By means of the test of mechanical property,the analysis of DSC and DMA,the conclusions were obtained as follows:The tensile strength of the film were increased by raised DMPA content,used polyester polyol system,increased 4,4-H₁₂MDI isomer content,raised the extent of latter chain extension and adopted two-shot method.