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Linear low and high density polyethylene sheets were compression molded and crystallized at a 5-10°C/min cooling rate. Parts of the sheets were annealed at different temperatures up to 2°C below the melting temperature. The small angle X-ray scattering (SAXS) and the wide angle X-ray scattering intensities of the annealed samples were studied. SAXS intensities showed particle scattering with a bimodal size distribution. The estimated radii of gyration were 15-17 nm and 5-7 nm, respectively. The crystallinity and the radius of gyration increased slightly with increasing annealing temperature for some samples; others did not show any change. No peaks characteristic of intercorrelated lamellar crystallinity in the SAXS intensities developed during the annealing. The original broad peak of high density polyethylene disappeared from the SAXS recordings on annealing. The length of the perfect chain versus melting temperature was calculated by the Thomson-Gibbs formula and Flory's concept of melting temperature depression where methyl groups and tertiary carbon atoms at the branches were regarded as second components (solvent). Linear relationships were found for both cases. Experimental data for a linear low density polyethylene obtained from the literature were in between the two functions. A lamellar model of crystallization corresponding to the data is proposed.
Linear low and high density polyethylene sheets were compression molded and crystallized at a 5-10°C/min cooling rate. Parts of the sheets were annealed at different temperatures up to 2°C below the melting temperature. The small angle X-ray scattering (SAXS) and the wide angle X-ray scattering intensities of the annealed samples were studied. SAXS intensities showed particle scattering with a bimodal size distribution. The estimated radii of gyration were 15-17 nm and 5-7 nm, respectively. The crystallinity and the radius of gyration increased slightly with increasing annealing temperature for some samples; others did not show any change. No peaks characteristic of intercorrelated lamellar crystallinity in the SAXS intensities developed during the annealing. The original broad peak of high density polyethylene disappeared from the SAXS recordings on annealing. The length of the perfect chain versus melting temperature was calculated by the Thomson-Gibbs formula and Flory's concept of melting temperature depression where methyl groups and tertiary carbon atoms at the branches were regarded as second components (solvent). Linear relationships were found for both cases. Experimental data for a linear low density polyethylene obtained from the literature were in between the two functions. A lamellar model of crystallization corresponding to the data is proposed.
SYNOPSISPolymeric matrices of poly (8-vinylpyridine) were prepared with application of gamma irradiation to its ethanolic solutions. The interaction parameter ( X ) between the polymer and the solvent, and the average molecular weight between the crosslinks ( M , ) were calculated from the swelling properties.
SYNOPSISSamples of ethylene/ 1-butene copolymer were fractionated according to chemical composition by preparative temperature rising elution fractionation ( T R E F ) in the range of 27-117OC. The resulting fractions were submitted to DSC, SEC, and FTIR analyses. For each fraction, the methyl group content, melting temperature, crystallinity, average molecular weight, and molecular weight distribution were determined. From the results, it was found that the melting temperature increased linearly with the extraction temperature in the range of low temperatures and remained constant at high temperatures. Similar behavior was observed for crystallinity. It was also verified that the first two fractions showed a higher degree of supercooling than the fractions extracted at higher temperatures. These results were explained by the existence of a heterogeneous intermolecular distribution of comonomer molecules. In a general way, the comonomer units, present at higher concentrations in the low temperature fractions, tended to destroy the crystalline order of the polymer.
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