J. Chojnowski, S. Rubinsztajn, L. Wilczek
Oct 1, 1987
Citations
0
Influential Citations
39
Citations
Journal
Macromolecules
Abstract
pentamethyldisiloxan-1-01 (3) were studied in dioxane and in methylene chloride solutions. The reaction is accompanied by some processes involving siloxane bond cleavage. The condensation of 1 in dioxane shows classical kinetics of ring formation with competing linear growth, complying with the dilution rule of cyclization enhancement. In contrast, this rule does not work for the process in methylene chloride since cyclization in this solvent exhibits the same second-order kinetics in the substrate as the intermolecular condensation. This is explained by the base autocatalysis of the process with the substrate, which picks up a proton from the silanol group exerting nucleophilic attack. This catalysis is intramolecular for linear growth and intermolecular for cyclic product formation (intra-inter catalysis). In dioxane solution this autocatalysis is not observed since it is dominated by the assistance of the solvent molecule. This mechanism was confirmed by comparison of kinetic results of the condensation of reactants 1,2, and 3 and by hydrogen bonding studies of these model oligomers.