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ABSTRACT:The effects of molecular weight and its distribution on fractural properties of polystyrene were studied at several elevated temperatures and various rates of strain. Logarithmic plots of ultimate strength ar against ultimate rate of strain i'r, as well as of ultimate strain rr against rr at various temperatures, can be superposed by horizontal shifting into respective smooth master curves, giving the same shift factors. The shift factors are of the WLF type.Fractural behavior can be distinguished into four regions: brittle to ductile, ductile, ductile to flow, and flow regions. The effect of molecular weight is notable especially in the third and fourth regions. ar and rr plotted against i'r become lower and lower as molecular weight decreases. When a low molecular weight component is included, ar and rr plotted against i'r shift to the short. time-scale (high-rate strain) side. KEY WORDSFracture / Polystyrene / Molecular Weight Distribution / Molecular Weight / Time-Temperature Superposition / The fractural properties of high polymers, especially of vulcanized rubbers and glassy polymers, have been studied by many authors 1 -3 and some results obtained in the field of linear viscoelasticity have been applied to these properties on the basis of the thought that the fractural properties are governed by the some relaxation processes. 4 -s On the other hand, according to Coleman 9 -11 and Kawabata, et al., 12 the fractural properties of fibers and vulcanized rubbers are essentially dominated by stochastic or statistic processes. Recent developments in studies of linear and nonlinear viscoelastic properties of uncrosslinked amorphous polymers are stimulating studies on fractural properties of these polymers. However, there have been only a few studies on effects of molecular weight and its distribution on the fractural properties of these materials.For several years, the authors have devoted themselves to research on the effects of molecular weight and its distribution on the rheological properties of several kinds of polymers such as polystyrene 13 ' 14 and poly(methyl methacrylate). 15 • 16

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Dynamic measurements are made with cone and plate geometry on the aqueous solutions place within 5 sec. This early stage of relaxation is the origin of production of zigzagshaped fibrillar structure in the fibers and films made from liquid crystalline solutions. The dynamic properties of cholesteric liquid crystals of HPC are not permanent but variable with the history of mechanical treatments. INTRODUCTION The monograph on rheology of liquid crystals by Porter and Johnson 1) published in 1967 drew attention to the new field of rheological science. Many original papers and monographs in this stimulating area have appeared so far in various journals. Most recently Asada and Onogi 2) reviewed the papers on the rheological properties of polymer liquid crystals focusing interest on their own rheo-optical studies. A general survey of the papers thus far published leads to the discovery of fact Plots of log G' and log G'' against log ƒÖ for 60 wt% solution of HPC in combined tests performed in the order, dynamic-steady shear-dynamic. Rate of shear at steady-shear flow, 1 sec-1. Dynamic measurements before steady-shear flow. Dynamic measurements after steady-shear flow.

Ethylene-propylene block copolymer (EPBC) is mainly composed of two component polymers, polypropylene (PP) and ethylene-propylene rubber (EPR). The dependence of morphologies as well as dynamic moduli of EPBC on the molecular characteristics of the components were investigated for four EPBC samples. From the results of the temperature dependence of dynamic moduli and the morphologies, it was suggested that the samples have heterogeneous structure composed of a dispersed EPR phase and a PP matrix phase in which a part of the EPR component dissolves. The concentration of dissolved EPR in the matrix increases with increasing propylene content of the EPR component. For the melts of the EPBC samples containing the EPR component of higher than about 70 wt% propylene contents, a secondary plateau was observed in the long time region on the dynamic viscoelasticity curves. To clarify the origin of this slow relaxation, the dynamic viscoelasticity were compared with three theories: Palierne's emulsion model, the thermal diffusional model and the blending rule. The comparison suggested that the blending rule can well explain the secondary plateau behavior originated from the existence of the high molecular weight EPR dissolved in the PP matrix.