Flow instabilities of epoxide prepolymers

Flow of molten epoxide prepolymer ( T g = 303 K, M̄ n 889, M̄ u / M̄ n = 1.46) shows stress jumps. A hydrodynamic explanation is forwarded, and a check of the theoretical jump is carried out, with shear viscosites and shear moduli measured at 361 K. The increase in pressure produces a decrease in volume, which increases the rigidity of the polymer, which is then reduced by relaxation of the compressed chain segments.