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The segmental size in amorphous poly(ethylene terephthalate) (PET) was determined by two methods: a) from deformational behavior of amorphous samples in the elastic state by optical birefringence measurement, and b) from dynamic behavior of a small spin probe by ESR measurement of correlation times. The use of the network model for orientation of segments in amorphous polymer and of the generalized free-volume model for re-orientation of the probe in the amorphous phase gave comparable values ofn=2.3 and 2.1 structural units/segment. We conclude that trans ⇌ gauche conformational transitions of rather small macromolecular segments are the basic motion mechanism in αa-segmental mobility in PET.

Free radicals were generated in a rigid rod-like copolymer via mechanical route and by gamma radiation. The (EPR) method was used for studying free radicals formed at 123 K. The spectra of free radicals observed and the influence of molecular motions on the transport of radical centers in the fracture surface layer are discussed.

A general version of the Kusumoto-Bullock free-volume model for reorientation dynamics of spin probe in solid polymers is described. Its application enables one to obtain simultaneously the size parameter of a segment and the kinetic-energy parameter of segmental mobility. These data, along with theoretical knowledge of the conformational microstructure and conformational dynamics, allow a discussion of molecular mobility in terms of concrete conformation-segmental motion mechanisms. Participation of one-barrier transitions of the typePptqQ→Pp′g ± q′Q, and two-barrier transition of the type gauche-migration, creation and annihilation of kink sequence was observed for linear polyethylene. In agreement with the conformational microstructure, it was found for isotactic polypropylene that Schatzki's crankshaft motions of four-member segments might be involved.