title: The polysiloxane cyclization equilibrium constant: a theoretical focus on small and intermediate size rings.
abstract: The nonlinear dependence of polysiloxane cyclization constants (log(K(x))) with ring size (log(x)) is explained by a thermodynamic model that treats specific torsional modes of the macromolecular chains with a classical coupled hindered rotor model. Several parameters such as the dependence of the internal rotation kinetic energy matrix with geometry, the effect of potential energy hindrance, anharmonicity, and the couplings between internal rotors were investigated. This behavior arises from the competing effects of local molecular entropy that is mainly driven by the intrinsic transformation of vibrations in small cycles into hindered rotations in larger cycles and configurational entropy.
authors.affiliation: CNRS, UMR 6296, Institut de Chimie de Clermont Ferrand (ICCF) , Photochimie, BP 80026, F-63171 Aubière, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Madeleine-Perdrillat
authors.forename: Florence
authors.initials: F
authors.lastname: Delor-Jestin
authors.forename: Pascal
authors.initials: P
authors.lastname: de Sainte Claire