A broad-line nuclear magnetic resonance investigation of polyacrylonitrile phase structure and chain conformation

The investigation of polyacrylonitrile (PAN) phase structure has been carried out in connection with its chain conformation by means of analysing the shape, width and the second moment of ¹H BL-n.m.r. lines. A complex structure of the n.m.r. lines within the range of temperatures between −180°C and 115°C is interpreted as resulting from the presence of a specific conformation in the iso- and heterotactic sequences of PAN. A complex shape of the lines in temperatures above 115°C may be explained by heterogeneity of phase structure or by the polymer's microstructure. The line width was found to narrow in the vicinity of 95°C and within the range of 120°C and 160°C, which was attributed to certain changes in the nature of molecular motion. Theoretical and experimental values of the second moment of ¹H BL-n.m.r. line for rigid lattice of PAN were compared. The n.m.r. spectra of two polyacrylonitrile samples heat-treated at 200°C and deuterated respectively, were studied to confirm the presence of specific chain conformation.