Flow birefringence (FB) has been investigated in solutions of products of hydrolytic degradation of poly(naphthoyleneimide
benzimidazole) (PNIB) in 96% sulphuric acid PNIB solutions have previously been subjected to heating at various temperatures
from 65 to 120°C and then investigated at 22°C by FB and viscometry. A monotonic decrease in intrinsic viscosity and the molecular
weightM of thermal degradation products with increasing degradation temperature was detected. At the same time, the shear optical
coefficients in series of products with decreasingM first increases and then, at treatment temperatures exceeding 90°C, decreases with decreasing [ν] in accordance with decreasingM of the product. Possible reasons for the detected anomaly have been discussed.
Authors:P. Lavrenko, O. Okatova, K. Andreeva, and B. Schulz
Translational diffusion of poly-2,5-(1,3-phenylene)-1,3,4-oxadiazole (PMOD) in solution in 96% sulphuric acid was studied,
and intrinsic viscosity was measured at different stages of thermal degradation. Polymer solution has previously been subjected
to heating at temperature ranging from 75 to 104C and then investigated at 26C. A monotonic decrease in intrinsic viscosity
and the molecular mass, M, of degraded products with increasing degradation temperature was detected. The rate constant of the degradation process
has been obtained from the change in M of the degradation products with time at a fixed solution temperature, and the activation energy of the process was calculated
by using the temperature dependence of the rate constant. The activation energy (E =1028 kJ–1 ) is close to that obtained previously for the hydrolysis of poly-2,5-(1,4-phenylene)-1,3,4-oxadiazole (PPOD) in sulphuric
acid (106 kJ–1 ), the rate constant being approximately twice in the value.