130℃～+100℃におけるポリプロピレンの分子運動

The effect of the microtacticity and aggregation on molecular motions within the stated temperature range have been studied. Samples of uniform molecular weight fractions and non fractionated polymer were subjected to a comprehensive characterization in respect of molecular weight, density, crystallinity %, type of crystallite and infrared absorption prior to molecular motion studies.<BR>Techniques employed in the study of molecular motions were dilatometry, differenti al scanning calorimetry (DSC), loss of mechanical modulus with temperature variation, and nuclear magnetic resonance (NMR).<BR>Inferences reached were as follows.<BR>1) Three kinds of transition points T_g1, T_g2 and T_g3 existed within the temperature range studied. Such transition temperatures were detected by dilatometry for both isotactic and atactic polymer.<BR>T_g1 was assigned to a localized mode of molecular motion in the amorphous regions and was quite independent of overall tacticity and crystallinity. However, T_g2 and T_g3 appeared to be strongly influenced by microtacticity.<BR>2) DSC indicated T_g1 and T_g2 values for the atactic polymer to be -60°C to -40°C and -20°C to -5°C respectively.<BR>3) The characteristic nature of specific-volume temperature relationships were readily accounted for by the observations (a) a rapid secondary crystallization of the smectic forms occured above room temperature, (b) this smectic form underwent transition to the monoclinic form over a wide temperature range above 70°C.<BR>4) Peak temperature of viscoelastic dispersion at room temperature fell off with decreasing micro-tacticity and there was a strong concomitant fall in the values of tangents to such peak temperatures. This dispersion could be accounted for as the glass transition due to the chains with lower microtacticity.<BR>5) NMR measurement indicated the occurence of partial motional narrowing at temperatures above -100°C. Such observations were suggestive of the independent existence of smaller “daughter” regions of microtacticity within the main phases. Motional narrowing due to the micro-Brownian movement in the amorphous phases could be initiated at higher temperatures for polymers of higher microtacticity. The NMR spectra of the isotactic polymer underwent no apparent change following heat treatment of the polymer. Change in the fraction ratio of broad to narrow line components were very marked at room temperature even for the sample of annealed polymers in which the crystallinity was constant. Above 50°C, melt grown crystals exihibited only a narrow line component, whilst the major part of the broad line component, was retained for solution grown crystals.