PHASE-SEPARATION AND CRYSTALLIZATION PHENOMENA IN A POLY(ESTER-CARBONATE) BLOCK-COPOLYMER - A REAL-TIME DIELECTRIC SPECTROSCOPIC AND X-RAY-SCATTERING STUDY

The change of the relaxation process associated with the long-range mo tions during crystallization of an amorphous poly(butylene terephthala te)-polycarbonate block copolymer (PBT-PC) has been followed in real t ime by means of measurement of the dielectric complex permittivity. Th e observed decrease of the dielectric strength has been correlated to the appearance of crystallinity as detected by real-time wide- and sma ll-angle X-ray scattering experiments using synchrotron radiation. The phenomenological Havriliak-Negami description has been used to analyz e the changes of the dielectric strength, central relaxation time, and shape parameters describing the relaxation as crystallization proceed s. The influence of the crystalline lamellae on the dynamics of the am orphous phase for the PBT-PC(60/40) thermoplastic elastomer has been e xamined and compared with the relaxation processes of related homopoly mers. The differences obtained are discussed by considering that PET b lock copolymers typically crystallize by formation of spherulitic supe rstructures in which the degree of crystallinity is smaller than in th ose formed by homopolymers. Finally, phase separation in the early sta ges of crystallization has been discussed on the basis of Cahn's linea rized theory of spinodal decomposition.