Folded-chain-lamellae are considered as "cooperative units" with frozen matter flow and with a locally heterogeneous atomistic order the degree of which is reversibly regulated by surface-meking or surface crystallization. A consequent thermodynamic treatment of restricted micro-phase equilibrium in semicrystalline fractions of polyethylene of different molecular weights can be shown to deliver a characterization of such nonequilibrium states by relating additional internal variables to parameters of the microstructure (DSC-measurements, electron-micrographs, SAXS). What appears to be very satisfactory is the conclusion that the excess situation produced by noncrystallizable defects in the semicrystalline samples is dearly related to the original state of order in the melt: Approximative invariance of penetration is directly elucidating that any matter flow in the regime of the chains of sufficient length is frozen during folded-chain crystallization. Molecular-weight effects in semicrystalline fractions of polyethylene can be interpreted on these lines.

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A theory of strain-crystallization of random networks comprised of stereoregular chains is developed. The crosslinks are assumed to be expelled from crystal cores. For this reason, the rubber is considered to be represented as a random eutectoid copolymer, the thermodynamics of strain crystallisation of which is described by the use of the van der Waals model of networks. The strain dependence of the maximum melting temperatures, the degree of crystallinity and the average thickness of the crystallites calculated are shown to be in fair accord with experimental data.