SAXS INVESTIGATIONS ON RELATIONSHIPS BETWEEN SYNTHESIS CONDITIONS AND SOLID-STATE DRAWABILITY OF HIGH-MOLECULAR-WEIGHT POLYETHYLENE NASCENT REACTOR POWDERS - SINTERING AND ANNEALING OF POWDERS

High and ultrahigh molecular weight polyethylene samples have been investigated by small angle X-ray scattering (SAXS) methods to study the structural changes induced by solid state drawing of nascent reactor powders. The results are correlated with prior reports of differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). The powders were prepared by two different Ziegler-Natta synthesis processes: polymerization in a slurry and in the gas phase. The synthesis temperature range was 30-85 degrees C. Monoclinic crystals were identified in samples synthesized at 30 degrees C. SAXS patterns have been recorded at different stages of the solid state processing. Results obtained on nascent reactor powders and on sintered and annealed powder specimens are discussed. No interference peak was ever detected. SAXS profiles obtained from all samples were consistent with the scattering produced by a polydispersed ensemble of particles having approximately globular shape. Values of the radii and of the weight fractions of these gobular aggregates were obtained by Gaussian analysis of their SAXS patterns, according to the iterative generalized Guinier approximation. Results obtained from nascent powders were consistent with five dimensional groups of globular particles. The dependence of weight fractions and globule dimensions on synthesis parameters was investigated. Values of the radii, R(i), of the S185 samples are quasi-multiples of 25 Angstrom, up to the top value of 450 Angstrom of the R(5) group. Such a multiplicity in the sizes of the globular aggregates can be attributed either to the clustering of small subunits into larger particles or to lamellar thickening by preferred doubling during synthesis. Volume contractions of the globular aggregates produced by annealing are more important in samples synthesized at a low temperature. Sintering reduces differences among the radii and the weight fractions of different samples. It is proposed that mobility of polymer chain segments is higher for samples synthesized by a slurry process at 85 degrees C, since modifications induced by sintering and annealing are more important for these samples. Thus the higher chain mobility and the higher ductilies obtained by slurry synthesis at 85 degrees C suggest that these conditions may lead to nascent powders having lower degrees of entanglement.