Polymorphism of syndiotactic poly(m-methylstyrene)

The synthesis and a preliminary structural characterization of syndiotactic poly(m-methylstyrene) are reported. A complex polymorphic behavior has bee n revealed. Three different polymorphic forms and two clathrate structures, characterized by the inclusion of guest molecules in the crystalline latti ce, have been found. The conditions for the obtaining of the various polymo rphic forms, in unoriented and. oriented fiber samples, are described. Form I, obtained by crystallization from the melt or from the amorphous phase, is characterized by chains in the s(2/1)2 helical conformation. The same he lical conformation has been found in the clathrate structures containing mo lecules of o-dichlorobenzene or benzene. Form II can be obtained by crystal lization from solutions of solvents which do not form clathrate structure o r by removing the guest molecules from the clathrate forms. Form III, obtai ned in oriented fibers by stretching amorphous films, is a mesomorphic modi fication characterized by chains in the trans-planar conformation with a hi gh degree of disorder in the lateral packing of the chains. Annealing treat ments or solvent-induced crystallization of the oriented mesomorphic form a llow the obtaining of oriented fibers in some of the polymorphic forms. The differences and analogies with the polymorphic behavior of syndiotactic po ystyrene and poy(p-methylstyrene) are outlined.