Synthesis And Characterization Of Reproducible Aqueous Isocyanate Micelles With Low De-blocking Temperature And Its Stability Research

Isocyanate compounds and polymers which have excellent environmental and adjustable performance, have been widely used in coatings, adhesives, leather finishing agents, textile finishing agents and so on. However, because of its active chemical properties isocyanate easily reacted with water and active hydrogen containing substances leading to difficult to stabilize, especially in the field of water-based paint and water-based polyurethane adhesive. Therefore, in this study, we introduced hydrophilic groups and blocked terminal isocyanate in the molecular structure of isocyanate prepolymer to make it stable and reactive in the aqueous solution, developing a functional and environmentally friendly adhesive with low deblocking temperature.Aqueous isocyanate micelles with low deblocking temperature by using N-methyl aniline (N-MBA), trichlorophenol (TCP) as blocking agent and aqueous isocyanate with a high molar ratio by using methyl ethyl ketone oxime (MEKO) were prepared respectively. It was researched that effects of the R value (NCO/OH molar ratio), anion content (DMPA) and neutralization degree on the morphology, particle size and distribution and reaction characteristics and blocking reaction kinetics of the blocking/deblocking of isocyanate micelles under the conditions of the different NCO/OH ratio, DMPA content and catalyst. Finally, stability mechanism of blocking micelles dispersing in aqueous solution was systematically researched.It was observed that the prepared blocked isocyanate dispersed stably with spherical micelles and uniform particle size in the aqueous solution by the SEM. With increasing DMPA content, the particle size of blocked micelles based aromatic (TDI) decreased and finally tends to an equilibrium value, particle size distribution become narrow, and dispersion stability increased, but the particle size of micelles based aliphatic (HDI) increased at first and had an little decrease finallyby increasing DMPA content, With the increase of R-value, the particle size of the micelles based aromatic (TDI) was enlarged at first and then gradually decreases, the dispersion stability become deteriorated, but the particle size for HDI micelles gradully decreased, prepared HDI micelles could be stable under conditions of high NCO/OH molar ratio (12.3), with the neutralization degree increased, the particle size gradually decreased and stability become increased.The characterization of blocking/deblocking was researched by DSC and FTIR method and it was shown that the characteristic absorption peak of NCO at 2267cm-1 disappeared in blocking prepolymer, stretching and deformation vibration of NH and stretching vibration of C=O at 1170cm-1 enhanced in deblocking process. MEKO blocking micelles a deblocked between 80～90℃ at first, the peak temperature were between 110～125℃, exothermic enthalpy were between 550-670J/g, therefore it achieved efficient deblockingreaction; initial deblocking temperatureof N-MBA blocking micelle were between 70～80℃, the peak temperature were between 105℃～110℃, initial deblocking temperature of TCP blocking micelles were between 62～70℃, the peak temperature were between 95～110℃, so it could be deblocked at low temperature conditions, the deblocking temperature not was affected in different R values and DMPA content.It was shown that reaction of TCP blocking NCO-prepolymer was determined as two order reaction by kinetic studies. Under no catalyst, the reaction activation energy Ea=43.890 KJ/mol, under the catalyst DBTDL, its reaction activation energy decreased at Ea=34.412 KJ/mol. The blocking reaction was essentially addition reaction of nucleophilic group to attack nucleophilic carbon atoms in the isocyanate. And the activation energy decreased under the catalyst leading to the reaction activity increased.The study on stability of blocked micelles showed when a higher blocking ratio, the stability was determined by hydrophilic groups, namely it was controlled by DMPA content. When the blocking rate was lower, the stability mainly depended on free isocyanate group content, i.e. the stability was determined by blocking rate. The stability of blocked micelles could be directly judged by initial Zeta potential, if the absolute value of the Zeta potential was not less than that the potential made micelles stable, the blocked micelles could stably dispersed in the aqueous solution. Under the premise condition that the structure of micelles was unspoiled, the micelles mainly were stable in an aqueous solvent by diffusion electric double layer and solvation effect.