Some linear low-density polyethylenes (LLDPEs) have been examined in detail by temperature rising elution fractionation (TREF), size exclusion chromatography (SEC), 13C NMR analysis, differential scanning calorimetry (DSC), and FTIR spectroscopy. From the results, the following have been concluded:(i) LLDPEs manufactured by four different processes have in common a characteristic intermolecular bimodal short-chain branching (SCB) distribution; (ii) the bimodal SCB distribution is caused by two kinds of active sites in Ti-based heterogeneous Ziegler catalysts, identified by the values of the reactivity ratio product (rxr2 = 0.5-0.6 and rxr2 = 1.0, respectively); (iii) one kind of active site, having an alternating character in the copolymerization (identified by rxr2 = 0.5-0.6), gives the higher SCB concentration peak in the bimodal SCB distribution and the lower molecular weight polymer, while the other kind of active site, having a random character (identified by rxr2 = 1.0), gives the lower SCB concentration peak and the higher molecular weight polymer.ABSTRACT: A mathematical representation based on a linear elastic theory is proposed by which one may investigate the dependence of the crystal lattice modulus in the chain direction on molecular orientation and crystallinity. This description indicates that the crystal lattice modulus as measured by X-ray diffraction is different from the intrinsic crystal lattice modulus. However, the numerical calculation indicates that the calculated value is almost independent of the molecular orientation and crystallinity except in the case of a low degree of molecular orientation and low crystallinity, although the calculated Young's modulus is strongly affected by them. Thus it turns out that X-ray diffraction has advantages in measuring the crystal lattice modulus exactly.

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Copolymerization of propene with 1-hexene was performed at 40 "C under atmospheric pressure using both aspecific and isospecific catalysts composed of TiCI,/MgCl, and AI(C,H,),, and of Solvay type TiCl, and Cp,Ti(CH,), (Cp: cyclopentadienyl), respectively. The isospecific catalyst gave two kinds of copolymers with different content of 1-hexene, whereas the aspecific catalyst gave a uniform copolymer abundant in 1-hexene. Both copolymers produced with the isospecific catalyst were found to show isotactic stereoregulation in the propylene units. From these results, it was concluded that the catalyst composed of Solvay type TiCI, and Cp,Ti(CH,), has two kinds of isospecifically active species which differ in the monomer reactivity ratio for propene-1 -hexene copolymerization.

SYNOPSISThe mean length and the indices of long-chain branches (LCBs) of a high-pressure lowdensity polyethylene (HPLDPE) as a function of molecular weight have been determined for its molecular-weight-fractionated parts by the I3C-NMR analysis and the viscosity measurements. The mean LCB length of the fractions was of the order of 200-300 carbons in length. The size of LCBs increases with increasing molecular weight, but the size of LCBs relative to the overall macromolecular size decreases with increasing molecular weight. The LCB sizes as a function of molecular weight determined for the fractions of one parent HPLDPE are in good agreement with those previously reported for HPLDPE whole polymers.

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