Determination and Temperature Dependence of Plateau Modulus for Polymerization of Propylene to Isotactic Polypropylene with Ultra-high Molecular Weight under Catalysis of Ziegler-Natta Catalyst

The viscoelastic behavior of isotactic polypropylene with ultra-high molecular weight(UHPPH) and broad molecular weight distribution(MWD), produced in the presence of Ziegler-Natta catalyst, was investigated by means of oscillatory rheometry at 180 and 200 ℃, whose loss modulus(G″) plots at 180 and 200 ℃ versus the natural logarithm of angular frequency(ω) present a pronounced maximum at 34.35 and 69.21 rad/s, respectively, and do not show a maximum peak at 0.01-100 rad/s for Ziegler-Natta catalyzing ethylene-propylene random copolymerization(PPR) with a conventional molecular weight and broad MWD. The fact indicates that the high molecular weight is responsible for a maximum peak of G″(ω) vs. lnω curves for UHPPH. This makes it possible to determine the plateau modulus(G 0_N) of UHPPH from a certain experimental temperature G″(ω) curve directly. For UHPPH, the G 0_N determined to be 4.28×10 5 and 3.62×10 5 Pa at 180 and 200 ℃, respectively, decreases with the increase of temperature and is independent of the molecular weight, which directly confirms reputation theoretical prediction that the G 0_N has no relation to the molecular weight.

RHEOLOGICAL PROPERTIES OF POLY(VINYLIDENE FLUORIDE) IN MOLTEN STATE

The theological behavior of poly(vinylidene fluoride)(PVDF)samples of different molecular weights was investigated by means of high pressure capillary rheometer and rotational rheometer.Information on the rheological properties of such materials above melt temperatures is of interest as this can lead to an improved understanding of polymer behavior in processing and fabrication technologies.Shift factors derived from time-temperature superposition showed good fit to the Arrhenius equation with a flow activa...

Preparation and Structure of Poly(ethylene-co-vinylacetate)/Montmorillonite Nanocomposites

Poly(ethylene-co-vinylacetate)/sodium montmorillonite(EVA/MMT)and Poly(ethylene-co-vinylacetate)/organophilic montmorillonite(EVA/o-MMT)nanocomposite were prepared by solid-state mixing.The morphology and structure of the composites were explored by scanning electron microscopy(SEM),wide-angle X-ray diffraction(WAXD),differential scanning calorimetry(DSC),and dynamic mechanical analysis(DMA).The results showed that the intercalated nanocomposite was successfully synthesized for EVA/o-MMT system,while in the EVA/MMT nanocomposite,MMT were poorly dispersed in the order of μm.An unexpected rubbery plateau modulus of EVA/o-MMT nanocomposite above melting point of EVA was explored by DMA.The possible origins of this high-temperature modulus were analyzed.

EFFECT OF CHEMICAL STRUCTURE OF POLYCARBONATES ON ENTANGLEMENT SPACING

The master curves of a series of aliphatic polycarbonates （APCs） with different lengths of methylene segments in the repeat unit were obtained by dynamic rheological measurements. The plateau modulus and entanglement molecular weight were determined and cross-checked by different methods. Though having distinct difference in chemical structure of repeat units, both APCs and bisphenol-A polycarbonates have the similar entanglement weight and entanglement spacing. On the other side, the plateau modulus decreases with increasing the length of the side group of aliphatic polycarbonates with different side-chain lengths in the literature. The packing length model can explain the relationship between chain structure and entanglements.