APPLICABILITY OF THE WLF EQUATION TO POLYURETHANE POLYOLS AND FILM PROPERTIES OF THEIR RESINS

The need to reduce solvent content of coatings in compliance to air po llution and other Statutory Regulations has led to major efforts to de velop high solids coatings. The reduction in molecular weight helps to achieve application viscosity by an increase in free volume. Various polyurethane polyols have been synthesised by reacting the diols with polyisocyanates. The molecular weight and polydispersity indexes of th ese polyols have been determined by gel permeation chromatography (GPC ). The viscosity of 50% polyol solutions in various solvents has been determined at different temperatures. The temperature dependence on vi scosity of solution of these polyols has been determined by the Willia ms, Landel and Ferry (WLF) equation. The non-linear regression analysi s has been solved by using Levenberg Marquardt's algorithm. It is foun d that non-linear regression analysis gives high correlation coefficie nts and very low overall residual errors. The variation in the values of constants A and B for each WLF equation in the polyol solution indi cates that these constants are system dependent. The values of constan ts A and B obtained for polyurethane polyols in a particular solvent h ave been used to calculate the values of glass transition temperature of the oligomer solution (T-gs) at different concentrations. The value s of T-gs are found to vary with concentration. As the concentration o f polymer increases there is an increase in the T-gs value. The tensil e properties and resistance to scratch of resins prepared using these polyols and butylated melamine formaldehyde are better than those of c onventional resins. The VOC content of these coating formulations is l ower than the value prescribed by the Environmental Protection Agency (EPA). (C) 1997 Elsevier Science S.A.