High-quality positron lifetime measurements (70 million total counts) are reported for polyethylenes (PEs) of different crystallinities (X c ϭ 3-82%). The specific volumes of the crystalline and amorphous phases (V c and V a , respectively) were estimated from density and wide-angle X-ray scattering (WAXS) experiments. Some samples (those with low values of X c ) were branched PEs, and those with high values of X c were linear PEs for which X c was varied with changes in the crystallization temperature. Both V c and V a increase with decreasing X c in the range 0% Յ X c Յ 56% (the branched PEs) but are constant for X c Ն 56% (the linear PEs). The lifetime spectra were analyzed with the MELT and LIFSPECFIT routines. Artifacts that can appear in the spectrum analysis were checked via an analysis of computer-generated spectra. Four lifetime components appeared in all of the PEs; the two long-lived ones are attributed to pick-off annihilation of ortho-positronium (o-Ps) in crystalline regions ( 3 ) and in holes of the amorphous phase ( 4 ). With increasing X c , 3 decreases from about 1.2 to 1 ns, 4 decreases from 3.0 to 2.5 ns, and the intensity I 4 decreases from 29 to 0%. An increase in I 3 from 6 to 12% was observed. A comparison with simulations shows that the true I 3 value approaches 0 for X c 3 0%. The decrease in I 4 is weaker than the increase in X c ; this leads to the conclusion that the apparent specific o-Ps yield in the amorphous phase I 4 Xc increases with X c . Possible reasons for this surprising results are discussed. The fractional free hole volume [h ϭ (V a Ϫ V occ )/V a , where V occ is the crystalline occupied volume] was estimated from density and WAXS results. Between X c ϭ 0 and 56%, h decreases from 0.151 to 0.090, but it does not change further above X c ϭ 56%. The mean size (v) of the local free volumes (holes) estimated from 4 decreases from 200 to 150 Å 3 . The number density of holes (N h ) calculated from these values (N h ϭ h/v) also decreases from 0.8 to 0.6 nm Ϫ3 in the range 0% Յ X c Յ 56%. The values of V a , V c , h, and N h increase with an increasing degree of branching but do not vary for linear PEs. The possible influence of a crystalline-amorphous interfacial phase (three-phase model) on the observed lifetime parameters is also discussed.

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The orientation behavior of isotactic polypropylene (iPP) in ␣and ␤-crystal form was investigated by rheo-optical Fourier transformed infrared (FTIR) spectroscopy. This method enabled quantification of the degree of orientation as a feature of structural changes during uniaxial elongation in not only the crystalline phase but also the amorphous one. Molecular orientation mechanisms can be successfully derived from experimental results. Generally, three mechanisms were detected for iPP: (1) interlamellar separation in the amorphous phase, (2) interlamellar slip and lamellar twisting at small elongations, and (3) intralamellar slip at high elongations. The third mechanism was favored by ␣-PP, whereas ␤-PP favored the second mechanism, which, in fact, was responsible for the different mechanical properties of both materials at the macroscopic level. On the other hand, crystallization conditions may have significantly affected the amorphous orientation. Nevertheless, for both iPP types the chains in the amorphous phase always oriented less than did those in the crystalline phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4478 -4488, 2004

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The deformation behavior of homogeneous ethylene‐1‐octene copolymers was investigated as a function of the crystallinity and the crystal size and perfection, respectively, by wide‐ and small‐angle X‐ray scattering using synchrotron radiation. The crystallinity and the crystal size and perfection, respectively, are controlled by the copolymer composition and the condition of melt crystallization. The deformation includes rotation of crystals, followed by plastic deformation and complete melting of the initial crystal population, and final formation of microfibrils. The process of rotation, plastic deformation, and melting of crystals of the initial structure is completed at lower strain if the size and perfection of the crystals, respectively, decrease, that is, if crystals thermally melt at lower temperature. The kinetics of the fibrillation of the initial structure seems independent of the crystal symmetry, that is, rotation and melting of pseudohexagonal and orthorhombic polyethylene crystals (as evident in low‐crystalline specimens) are similar. The structure of the microfibrils, before and after stress release, is almost independent of the condition of prior melt crystallization, which supports the notion of complete melting of the initial crystal population. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1919–1930, 2002