NMR Approach to Kinetics of Polymer Ordering in Polyacrylonitrile Solutions and Acrylonitrile-Sodium Methallylsulfonate Copolymer Solutions: Solution-Concentration and Polymer-Tacticity Effects

摘要

Partial crystallinity of polyacrylonitrile and acrylonitrile-sodium methallylsulfonate copolymer is detected by X-ray diffraction in dimethyl formamide and glycerol-dimethyl formamide solutions in the range of polymer concentration (0.14, 0.325 mol/mol). Kinetics of isothermal ordering are followed by NMR for various temperatures, polymer concentration of the solutions and polymer tacticities. The rate of polymer ordering increases upon either a decrease of the temperature, an increase of the polymer concentration or an increase of the percentage of isotactic triads. Mandelkern's model of isothermal polymer crystallisation is applied to estimate the size of critical crystalline nuclei. Assuming that crystallites growth is negligible along polymer chain axis, one can deduce the maximal size of crystallites along this axis. The size of the crystallites perpendicularly to polymer chain axis is evaluated by X-ray diffraction. It is found to be of the order of 100 A.