TIT# Oriented quiescent crystallization of polyethylene studied by USAXS.
     Part 1: Observations of nanostructure evolution
AUT# Stribeck, Norbert; Almendarez Camarillo, Armando; Cunis, Sabine;
     Bayer, Rüdiger K.; Gehrke, Rainer;
SOU# Macromol. Chem. Phys. (2004), in print
LOC# xv083
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ABS# Highly oriented high-pressure injection-molded (HPIM) rods from
     polyethylene (PE) are heated until the discrete small-angle X-ray
     scattering (SAXS) has vanished. Thereafter non-isothermal and isothermal
     crystallization is investigated in situ by means of ultra small-angle
     X-ray scattering (USAXS). Orientation of the crystallites can be
     controlled by choice of the melt annealing temperature (shish-kebab model:
     memory, or self-nucleation effect caused by stable shishs). Both the
     scattering patterns and the multidimensional chord distribution function
     (CDF) are interpreted. A three-stage model of crystallization is
     developed. This model comprises row structure nucleation, almost
     statistical insertion of extended lamellae, and finally the insertion of
     blocky crystallites.
     It is found that the nanostructure evolution in the isotropic fraction of
     the material is the same as in the highly oriented one. The lateral
     extension of the lamellae is largest during isothermal crystallization.
     Correlation among domains is increased by non-isothermal crystallization.
     The shishs in the core of the HPIM rod appear less stable than those in
     the shell. Lobe-shaped reflections observed during and after quenching
     are not due to an orientation distribution of layer stacks, but reflect
     a correlation between long period and lateral extension of crystallites.
     During quenching a lateral modulation of the layer peaks in the CDF grows
     strong and shows the arrangement of block-shaped crystals proposed by
     Strobl to be the prcursors of lamellae. The thin lamellae formed during 
     rapid cooling are built from a central block surrounded by one or two 
     rings of satellites. The long period observed in the scattering pattern 
     during quenching is caused from correlations among crystalline blocks in 
     a chain, and not from correlations among lamellae.