Reversible crystallization and the rigid–amorphous phase in semicrystalline macromolecules

Abstract

Linear, flexible macromolecules in the semicrystalline state have long been recognized as being globally metastable and divided into microphases and nanophases with strong, covalent bonds crossing the phase boundaries. The different phases can be crystals, mesophases, liquids, and glasses. The glasses may have structures which correspond to liquids or mesophases and can exist even above the glass transition temperature of the mobile macrophase as rigid–amorphous fractions. This multilevel structure causes rather unique properties which vary with the thermal and mechanical history of the materials. Temperature-modulated calorimetry and related techniques which can separate equilibrium and nonequilibrium responses are ideal for the analysis of such structures. The techniques of thermal analysis needed to separate reversible from irreversible processes is described, and the transitions of the rigid–amorphous phase and the major reversible processes involving latent heats is discussed on hand of the literature. As baselines for this discussion, the vibrational heat capacity of crystals and glasses of the ATHAS Data Bank will be used.