No abstract

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.

ABSTRACT:Qualitative and quantitative analysis of short chain branches was carried out on a series oflow-density polyethylenes by Fourier transform infrared spectroscopy. The peak position of the methyl symmetrical deformation bands around 1378 em -1 was found to vary with the type of branches and used for identification of the branch type in low-density polyethylenes. The reciprocals of extinction coefficients of the methyl deformation bands were determined for various branch types on the basis of 13 C NMR data. The values changed from 0.39 to 0.76 depending on the type of branch. The methyl rocking bands ranging from 880 to 940 em -1 were examined using brominated samples. The peak positions also depended on the type of branch. For the methylene rocking bands, the peak at 772.2 em -1 due to the ethyl branch was clearly observed, but that due to the n-butyl branch was not detected around 745 em -1 , indicating the n-butyl absorption to be located very close to 730cm-1 rather than 745cm-1

No abstract

No abstract