Crystallization from the melt of alpha and beta forms of syndiotactic polystyrene

The crystallization of trans-planar alpha and beta forms of syndiotactic polystyrene is studied through X-ray diffraction and DSC analyses of melt-crystallized samples. The factors controlling the crystallization of the two forms are analyzed. Pure alpha and beta forms of syndiotactic polystyrene can be easily obtained setting the maximum temperature at which the melt is heated and the permanence time of the melt at this temperature. The crystallization of the alpha and beta forms does not depend on the crystallization temperature, at least in the range of accessible crystallization temperatures, between 240 and 270 degreesC, but only depends on the presence of the 'memory' of the alpha form in the melt. The most important factors are, indeed, the crystalline form of the starting material used in the melt crystallization experiments and the maximum temperature of the melt. Relevant recrystallization phenomena, occurring during the melting of the samples crystallized from the melt at low crystallization temperatures, are responsible for the complex melting behavior of the alpha and beta forms. The recrystallization involves only lamellar thickening of the crystals of the same form (alpha or beta) and not structural transformation. (C) 2003 Elsevier Science Ltd. All rights reserved.