The relaxation and equilibrium behaviour of model polyurethane networks

Summary The mechanical, dielectric and rheo-optical behaviour of model networks prepared from OH-terminated poly(oxypropylene)triols and 4,4-diphenylmethane diisocyanate with various molar ratios of hydroxyl to isocyanate groups, r_H=0.95 to 1.7, was investigated. The observed independence of the stress-optical coefficient of r_H indicates the homogeneity of networks. Networks prepared with r_H1 exhibit a narrow transition zone indicating a narrow chain distribution. With increasing r_h, the transition becomes distinctly broader; dielectric measurements are well correlated with the mechanical ones. The equilibrium modulus markedly decreases with increasing r_H.Presented at the 7th IUPAC Discussion Conference Polymer Networks, Karlovy Vary, CSSR, September 15–19, 1980