An anomalous tacticity-crystallinity relationship: A WAXD study of stereoregular isotactic (83-25%) poly(acrylonitrile) powder prepared by urea clathrate polymerization

A detailed wide-angle X-ray diffraction (WAXD) study was carried out for a series of stereoregular poly(acrylonitrile)s (PANs) having different isotac ticities (83-25%). The degree of crystallinity did not depend on the extent of their isotacticity, as confirmed by three WAXD evaluation procedures re ported previously. However, the main peak shifted from 17.1 to 16.8 degrees , and the half value width of the main peak decreased (1.70 to 0.97 degrees ) with an increase in stereoregularity. Drastic WAXD changes were observed when PAN was dissolved in a good solvent and recovered. The specific tactic ity-crystallinity independent relationship of stereoregular PAN powder is d iscussed in connection with the polymerization mechanism in the urea clathr ate at low temperatures.