Nonisothermal crystallization of high density polyethylene (HDPE)/maleic anhydride-modified HDPE(manPE)/ nanoscale calcium carbonate (CaCO 3 ) nanocomposite was investigated by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC). WAXD indicated that the crystallinity was reduced with the addition of CaCO 3 . The spherulite size of HDPE increased in the presence of manPE, but decreased when CaCO 3 was added from observation of POM. A modified Avrami analysis, Ozawa analysis, and Liu analysis were applied to the nonisothermal crystallization process. Crystallizability followed the order: HDPE/manPE/ CaCO 3 > HDPE/CaCO 3 > HDPE/manPE > HDPE when undercooling was taken into account. Dependence of the effective activation energy on the relative crystallinity was estimated by the Friedman equation, and the results were used to calculate the parameters (K g and U*) of Lauritzen-Hoffman's equation by Vyazovkin's method. These results indicate that the addition of maleic anhydride groups and CaCO 3 tend to promote the nucleation of spherulites on their surfaces and lead to epitaxial growth of the crystallites. But at the same time, manPE and CaCO 3 particles may hinder the transport of the molecule chains resulting in a decrease of the crystallization growth rate. POLYM. ENG.

Nonisothermal crystallization of polylactide (PLA)/silica composites prepared by (i) directly blending the PLA with nanoscale colloidal silica sol and by (ii) a solgel process are studied by differential scanning calorimeter (DSC) at various heating rates. Samples quenched from the molten state exhibited two melting endotherms (T ml and T mh ) due to melt-recrystallization during the DSC scans. Lower heating rate and the presence of silica particles generate a lower peak intensity ratio of T ml /T mh . The nonisothermal crystallization kinetics is analyzed by modified Avrami model, Ozawa model, and Liu-Mo models. The modified Avrami and Liu-Mo models successfully described the nonisothermal cold crystallization processes, but Ozawa is inapplicable. The nucleation constant (K g ) is calculated by modified Lauritzen-Hoffman equation and the activation energy by Augis-Bennett, Kissinger, and Takhor models. These calculated parameters indicate consistently that the nanoscale silica particles seem to form more heterogeneous nucleation to increase crystallization, but microscale one form hindrance to retard crystallization.

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Two soluble fluorescent polymers, poly(2-decyloxy-5-(4 0tert-butylphenyl)-1,4-phenylenevinylene) (DtBP-PPV) and poly(2-decyloxy-1,4-phenylenevinylene) (DO-PPV), were prepared by a method similar to the Gilch procedure. The DtBP-PPV and DO-PPV have a same chemical structure except for the conjugated tert-bytulphenyl substituents in the former. The polymers are characterized by using 1 H NMR, FTIR, UV-vis, photoluminescence (PL), and electroluminescence (EL) spectroscopies and thermogravimetric analysis (TGA). The 1 H NMR spectra show no tolane-bis-benzyl (TBB) structure defects in DtBP-PPV but some in DO-PPV. Both UV-vis absorption and PL emission peaks of the DtBP-PPV exhibit a red-shift phenomenon as compared with those of the DO-PPV. Moreover, with the DtBP-PPV and DO-PPV acting as light-emitting polymers separately, EL devices were fabricated with a sequential lamination of ITO/PEDOT/DtBP-PPV (or DO-PPV)/ Ca/Ag. The DtBP-PPV-based device shows a lower turnon voltage, a longer EL emission wavelength, and a higher brightness than the DO-PPV-based device. The maximum brightness of DtBP-PPV-based device is 57 cd/ m 2 at an applied voltage of 12 V.