POLYMORPHISM AND CHAIN CONFORMATIONS IN THE CRYSTALLINE FORMS OF SYNDIOTACTIC POLY(1-BUTENE)

A preliminary structural characterization of syndiotactic poly(1-butene) (s-PB) is presented. X-ray diffraction analyses on powder and fiber samples show that s-PB can crystallize in two different crystalline forms, named form I and form II. Helical symmetries s(2/1)2 and s(5/3)2 with repetitions of 7.73 and 20.0 angstrom have been found for the chains in form I and form II, respectively. Different conformations of the lateral groups of the chains for the two crystalline forms are suggested on the basis of conformational energy calculations as well as of comparisons between the X-ray diffraction patterns and the calculated Fourier transforms for isolated model chains.