1,721,008 research outputs found
Models of Adjacent Re-Entry Folds in the b Form of Syndiotactic Polystyrene. Conformational and Packing Analysis by Molecular Mechanics
No full textThe role of molecular mechanics in the prediction of the chain conformation of polymers in the crystalline state: Syndiotactic polymers
No full textModels of Adjacent Re-Entry Folds in the b Form of Syndiotactic Polystyrene. Conformational and Packing Analysis by Molecular Mechanics
No full text
The role of molecular mechanics in the prediction of the chain conformation of polymers in the crystalline state: Syndiotactic polymers
No full textENERGETIC FEASIBILITY OF ADJACENT REENTRY CHAIN FOLDING IN CRYSTALS OF ISOTACTIC POLYPROPYLENE
No full textConformational energy calculations for the alpha-form of isotactic polypropylene were carried out for possible adjacent re-entry fold schemes resulting from the inherent directionality of isotatic chains and from examination of the crystalline structure. The calculated fold conformational energy is compatible with the literature values of fold surface free energy
Oxidations of Benzyl and Phenethyl Phenyl Sulfides. Implications for the Mechanism of the Microsomal and Biomimetic Oxidations of Sulfides
No full textThe study of the oxidation of 4-methoxyphenethyl phenyl sulfide and 3,4-dimethoxyphenethyl phenyl sulfide with potassium 12-tungstocobalt(III)ate [Co(III)W] suggests that in the radical cations of 3,4,5-(MeO)(3)PhCH2SPh (4) and 2,4,6(MeO)(3)PhCH2SPh (5) the positive charge is not localized on the sulfur atom, but in the benzylic aromatic ring. Nevertheless, in the biomimetic and microsomal oxidation of 4 and 5 the products observed are exclusively sulfoxides and sulfones, which appears in contrast with a mechanism involving the formation of an intermediate sulfide radical cation followed by a fast oxygen rebound. A direct oxygen transfer mechanism seems most likely
ANALYSIS OF CHAIN FOLDING IN CRYSTALLINE ISOTACTIC POLYPROPYLENE - THE IMPLICATIONS OF TACTICITY ANDCRYSTALLOGRAPHIC SYMMETRY
No full textTacticity and crystallographic considerations are used to predict fold models for a perfect crystal of isotactic polypropylene (α-form). If we assume adjacent re-entry chain folding we conclude that the folding plane must be parallel to the (010) plane. This is in agreement with morphological experimental evidence. We also show that this result is likely to apply even to non-perfect crystals
Influence of the Temperature on the Crystal Structure of poly(p-phenylene sulphide): A Study by X-Ray Measurements and Molecular Mechanics
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