OBSERVATION OF A SUPER-GLASS-TRANSITION EVENT IN THE DAMPING SPECTRA OF AMORPHOUS BLOCK COPOLYMERS

The dynamic thermomechanical spectra of several block copolymer systems have been studied in the frequency range 3.5 to 110 Hz. The samples were either ABA triblock copolymers or cruciform block copolymers, where A is polystyrene and B is either polybutadiene or an ethy lene-but-1-ene random copolymer. Specimens for measurement were prepared from films cast using different solvents, either in the presence or absence of a cross-linking agent, di-tert-butyl peroxide. It was observed that when uncross-linked films were cast from solvents which had solubility parameters similar to polystyrene, the films had sufficient mechanical strength to allow dynamic mechanical measurements to be made at temperatures up to 60 K higher than the glass-transition temperature of the polystyrene block. This revealed the existence of a super-glass-transition process which is termed Tu. Lightly cross-linked samples also exhibited this process but the intensity of the damping associated with Tu decreased with increasing cross-link density. Measurements of the apparent activation energies ΔH* for the glass- and super-glass-transition processes showed that ΔH* for the latter was consistently lower. While the existence of a Tu is confirmed, its molecular origins remain obscure. © 1979, American Chemical Society. All rights reserved.