ISSN:
0098-1273
Schlagwort(e):
Physics
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
In light of novel and problematic diffraction patterns arising through the thermoreversible gelation of isotactic polystyrene, the conformational possibilities were examined with particular reference to other conformational works published recently on this polymer. The specific objective was to ascertain whether highly extended, helical backbone geometries such as are required by the new x-ray patterns are possible or not with a purely isotactic arrangement of side groups. The first realization was that the recently announced low-energy, near-trans conformations are not relevant to the present issue as they do not provide the required extended geometry. Further, specific sampling of the conformational energy map revealed that the required high chain extension may be energetically feasible, contrary to traditional conceptions and to recent conformational calculations elsewhere. The divergences as regards the latter were traced to the specific choice of nonbonded atomic radii - all within generally accepted limits - which accordingly has a crucial effect even to the extent whether specific conformation types are forbidden or energetically stable. The implications this has for conformational analysis in general are being pointed out. While the novel crystal structure has not been solved, the present study at least eliminates the previously believed categoric objections to it being associated with isotactic chains and, beyond this, opens up new perspectives as regards conformational possibilities in polyolefins. The more general problems concerning the nature and origin of the gelation phenomenon nevertheless remain.
Zusätzliches Material:
3 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1980.180180106
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