Structurization in the poly (m‐phenylene isophthalamide)–dimethylacetamide system

Abstract

AbstractThe methods of turbidity spectrum and viscometry have been used to investigate structurization in the concentrated solutions of poly (m‐phenylene isophthalamide) (Pm‐PIPA) in dimethylacetamide (DMA). The kinetics of formation of the supermolecular order (SMO) were studied under isothermal conditions within the temperature and concentration range of 30 to 150°CC and 5 to 25 g/dl, respectively. Two stages of formation of SMO were observed, viz., a comparatively slow stage and after that a very fast increase in the SMO level. In the first stage, the average particle radius, rλ, decreases, which probably is related to the continuous formation of nuclei. In the second stage, rλ and the turbidity, τ, of solution increase steeply. In the same stage, an increase in the viscosity of solution was also observed. A diagram of the properties of the system was constructed, which is analogous to the phase diagram. The temperature limit of the stability, Tbi, fulfills the requirement of Vτ = 0, where Vτ (the rate of increasing turbidity), was determined. Tbi determines the binodal curve depending on the polymer concentration. The temperature limit of absolute instability, Tsp, fulfilling the requirement of Vτ→∞, was determined. Depending on the concentration of solution, Tsp was identified with a spinodal curve. The property diagrams obtained are characteristic of the curves of amorphous separation with the lower critical solution temperature. With increasing molecular weight, Mζ, Tc decreases. Additions of a third component cause a deformation of the binodal curve and shift it to higher (lithium and calcium chlorides) or lower (water) temperatures. The time, ts, of reaching a certain level of SMO during thermostabilization at T = 80°CC was taken as a measure of stability of technological solutions.