TIT# Nanostructure of atmospheric and high--pressure crystallised
     poly(ethylene--2,6--naphthalate)
AUT# Garcia Gutierrez, Mari Cruz; Rueda, Daniel; Baltá Calleja, Francisco J.;
     Stribeck, Norbert; Bayer, Rüdiger K.;
SOU# J. Mater. Sci. (2001), 36(24), 5739-5746
LOC# xv061
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ABS# Poly(ethylene-2,6-naphthalate) (PEN) materials were prepared by
     crystallisation from the melt. Pressure, temperature and duration were
     varied. Samples were investigated utilising small-angle X-ray scattering
     (SAXS), wide-angle X-ray scattering (WAXS), differential scanning
     calorimetry (DSC), and density measurement. Results are compared to
     findings from studies on similarly prepared samples from
     poly(ethylene terephthalate) (PET). SAXS was analysed using the
     interface distribution function (IDF) method. Materials prepared at
     ambient pressure were quenched during the advance of secondary
     crystallisation. The resulting crystallinity inside the layer stacks
     is almost constant at 60%, whereas the volume filled with those stacks
     increases as a function of crystallisation time and temperature. For
     crystallisation temperatures above 200°C secondary crystallisation goes
     along with a dynamic rearrangement of the primary stacks, as concluded
     from variations of the layer thickness distributions in the SAXS data.
     For crystallisation temperatures below 200°C primary lamellae are stable
     and both insertion of new crystals into existing stacs and generation of
     complete additional stacks is found. In contrast to PET, different kinds
     of layer stacks are not observed in any PEN nanocomposite. A nanocrystalline
     phase as observed in PET (with extremely thin amorphous layers separating
     crystalline lamellae) is not observed in PEN. Materials prepared at
     400 MPa exhibit high roughness of the crystalline domain surfaces. As
     a function of increasing crystallisation temperature there is a
     continuous transformation from $\alpha$- to $\beta$-modification, but
     almost no change of the long period. Crystalline thickness grows at the
     expense of both the amorphous thickness and the volume filled by lamellar
     stacks. Bimodal DSC thermograms can be explained by an additional
     component of uncorrelated nanosize crystallites.