1,720,994 research outputs found
UNDECAD RESOLUTION OF POLYPROPYLENE STEREOSEQUENCES - QUANTITATIVE-EVALUATION OF C-13 NMR METHYL SPECTRUM
No full textThe quantitative evaluation of a 50.3 MHz 13C NMR methyl spectrum of a particular stereoisomer of polypropylene, called hemiisotactic (hit-PP), was performed by a full lineshape fitting procedure. This sample presents a dramatic selection between stereosequences and a characteristic pattern of signal intensities. The results are compared with a general statistical approach, leading to the conclusions that the structure of hit-PP is almost pure (96%). Also, small deviations from the ideality are accounted for. In this way linewidths and chemical shifts have been established for nine nonads and five undecads of monomer units, calling for a sensitivity to carbon atoms distant up to ten bonds
Stretching polymer chains: conformational behaviour of syndiotactic polypropylene in metastable and stable phases
No full text
MAS NMR characterization of syndiotactic polypropylene: crystal structure and amorphous phase conformation
No full textINCLUSION POLYMERIZATION IN PERHYDROTRIPHENYLENE STUDIED BY ELECTRON-SPIN-RESONANCE SPECTROSCOPY - GROWING CHAIN STRUCTURE AND CONFORMATION OF METHYLSUBSTITUTED POLYBUTADIENES
No full textInclusion polymerization of diene monomers promoted by gamma rays and performed in perhydrotriphenylene was studied by ESR techniques. During polymerization of butadiene, 1,3-pentadiene, isoprene, 2,3-dimethylbutadiene, 2-methylpentadiene, and 2,4-hexadiene, spectra attributable to allyl-type radicals were collected. It was demonstrated they actually represent the propagating radicals and they do not vary over a long period of time. They are not temperature dependent in the range minus 150 degree / plus 60 degree C, apart from the radical of polybutadiene, suggesting that the included methyl-substituted polybutadienes are conformationally fixed. When the two opposite insertions of monomers 1,4 and 4,1 are distinguishable, the radicals bearing the higher number of methyl groups at the ends of allyl system prevail
Syndiotactic polypropylene after drawing: the effect of stretching polymer chains on MAS NMR
No full textPolyetylene Glycols as host solvents: applications to organic synthesis
No full textPolyethylene glycols (PEG) are fair solvents for inorganic salts and organic substrates; their use in some organic reactions is described
- …
