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The crystallization behavior and morphology of polyoxymethylene (POM) and POM with polyamide (PA) were studied by polarized light microscopy (PLM), isothermal and nonisothermal differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The isothermal crystallization kinetics were analyzed with the Avrami equation. Compared with the virgin POM, the addition of PA can reduce the spherulites size and improve the crystallization growth rate and crystallinity ([X.sub.c]) of POM, which demonstrates that the nucleation effect of PA as the high-molecular nucleus is favorable to the mechanical properties and dimension stability of POLYM. ENG. SCI., 45:1174-1179, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION In the mold processing of polymers, crystallization is a universal phenomenon, especially for polymers with regular molecular chains. Differences of crystallinity, crystal structure, and morphology will influence the properties [...]

Abstract: An interference-free tandem catalysis based on iron catalyst and TiCl4/MgCl2, activated by MAO, was used to prepare branched polyethylene by polymerization of ethylene. No obvious deactivation due to the side reaction of catalysts and cocatalysts was detected during the reaction process, which commonly existed in tandem catalytic systems based on conventional Ziegler–Natta catalysts. A series of branched polyethylene with different properties have been prepared by adjusting of reaction temperature, Fe/Ti molar ratio and the amount of MAO used. The alteration of oligomers concentration in the reaction system, by changing of reaction conditions, led to the products with different branching degrees, thus the thermal properties and molecular weight. The products obtained in toluene at lower Fe/Ti ratios exhibited better morphology than those obtained at higher Fe/Ti ratios. [Copyright &y& Elsevier]