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Thermochemistry of Redistribution of Poly[oxymulti(dimethylsilylenes)], —[(Me 2 Si) m O] n —, to Polysiloxanes and Polysilanes. Theoretical Study
Author(s) -
Cypryk Marek
Publication year - 2001
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/1521-3919(20010301)10:3<158::aid-mats158>3.0.co;2-r
Subject(s) - thermochemistry , chemistry , disproportionation , heterolysis , redistribution (election) , enthalpy , standard enthalpy of formation , exothermic reaction , homolysis , ab initio , standard enthalpy of reaction , computational chemistry , thermodynamics , catalysis , organic chemistry , radical , politics , political science , law , physics
Poly[oxymulti(dimethylsilylenes)], —[(Me 2 Si) m O] n —, are thermodynamically unstable and undergo exothermic base‐catalyzed bond redistribution producing polydimethylsiloxanes and polydimethylsilanes. The enthalpy and free energy of redistribution of model hydrogen‐substituted polyoxydisilylenes, —[(H 2 Si) 2 O] n — were calculated by ab‐initio methods (DFT and CBS‐4). Thermochemistry of polyoxydisilylene disproportionation was compared with analogous hypothetical reaction of poly(ethylene oxide). The enthalpies of reactions were calculated to be ca. –10 kcal/SiSiO and –6 kcal/CCO, respectively. Calculations show that the thermodynamic stability of polysiloxanes and polyacetals, respectively, due to the n O → σ* XO hyperconjugation, where X = Si, C, is the main driving force for these reactions. The difference in reactivity between polyoxymultisilylenes and polyethers has a kinetic origin and may be explained by the difference in activation energies associated with heterolytic cleavage of the X—X and X—O bonds.