CRYSTAL-STRUCTURE OF FORM-III AND THE POLYMORPHISM OF ISOTACTIC POLY(4-METHYLPENTENE-1)

A preliminary model for the crystal structure of form III of isotactic poly(4-methylpentene-1) is suggested on the basis of structure factor calculations. Chains in 4(1) helical conformations are packed in a te tragonal unit cell with axes a = 19.38 angstrom and c = 6.98 angstrom; the space group is I4(1). The polymorphic behavior of poly(4-methylpe ntene-1) is discussed on the basis of conformational energy calculatio ns on the isolated chain. The presence of different modifications is i n accordance with energy minima present in the conformational energy m ap.