Gelation of concentrated polymer solutions. I. Structural changes accompanying the isothermal gelation of polyacrylonitrile solutions

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Abstract
Isothermal gelation of concentrated solutions of polyacrylonitrile and acrylonitrile–methyl methacrylate copolymer in water containing dimethylformamide was followed with viscosity, light scattering, and wide‐angle, x‐ray diffraction techniques. It was found that in some cases gelation is accompanied by a strong change of light‐scattering characteristics, indicating heterogeneities in the range above 100 ÷ 200 A. In some cases also appear x‐ray diffraction rings in the gels, characteristic of crystalline order. However, all these changes were found to be not specific for the gelation process, and are believed to be connected with other processes (e.g., polymer precipitation) which accompany the gelation. It was also found that the structure of gels (as determined by light‐scattering and x‐ray diffraction) is determined as well by the composition and temperature of the system as by its thermal history.

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