The coupling reaction of silyl hydrides with alkoxysilanes to produce siloxanes and hydrocarbons catalyzed by tris(pentafluorophenyl)borane was studied by gas chromatography and UV spectroscopy using model reagent systems:  Ph2MeSiH + Ph2MeSiOn-Oct (I) and Ph2MeSiH + Me3SiOn-Oct (II). Detailed kinetic studies performed for system I showed that the reaction is first order in both substrates and the rate is proportional to the catalyst concentration. A highly negative apparent entropy of activation points to a crowded transition state structure, leading to a significant dependence of the rate on steric effects. Studies of system II demonstrated that the exchange of the Si−H and Si−OR functionality accompanies the coupling process and in many cases is the dominating reaction in this system. Ultraviolet spectra recorded during the reaction show a distinct strong absorption band with λmax = 303−306 nm, which is due to an allowed electronic transition in the uncomplexed B(C6F5)3 molecule. This absorption also gives rise to intense fluorescence with a maximum of the emission band at 460 nm. When the borane is complexed by oxygen nucleophiles, such as water, alcohol, or silanol and is not active as a catalyst, it does not show the absorption in the 303−306 nm region. This absorption may serve as a measure of the concentration of the active uncomplexed catalyst in the reaction system. Since complexes of B(C6F5)3 with the alkoxysilane substrates and the disiloxane products are relatively weak, the catalyst appears in the reaction system mostly as an uncomplexed species and its concentration is not significantly changed during the reaction. The mechanism proposed includes the transient formation of a complex between hydrosilane, borane, and alkoxysilane in which H- is transferred from silicon to boron and an oxonium ion moiety is generated by interaction of alkoxysilane with positive silicon. The decomposition of the complex occurs by the H- transfer to one of the three electrophilic centers of the oxonium structure, which explains the competition between the siloxane formation and the Si−H/Si−OR exchange. In the case of alkoxysilanes derived from primary alcohols, H- is preferably transferred to silicon. However, for alkoxysilanes derived from a secondary alcohol, such as isopropyl alcohol, the secondary carbon is more readily attacked than silicon by H-, which leads to a high yield of mixed disiloxane.

Statistical and block all‐siloxane copolymers containing quaternary ammonium salt (QAS) groups with biocidal activity as lateral substituents were synthesized as models for the study of the effect of the arrangement of the QAS groups in the copolymer chain on their antimicrobial activity. The bioactive siloxane unit was [3‐n‐octyldimethylammoniopropyl]methylsiloxane, and the neutral unit was dimethylsiloxane. The copolymers also contained siloxane units with unreacted precursor 3‐chloropropyl or 3‐bromopropyl groups. A small number of units containing highly hydrophilic 3‐(3‐hydroxypropyl‐dimethylammonio)propyl groups were introduced to increase the solubility of the copolymers in water. The bioactive and bioneutral units were arranged in the polymer chain either in blocks or in statistical order. The block copolymers differed in the number and length of segments. The copolymers were obtained by the quaternization of tertiary amines by chloropropyl or bromopropyl groups attached to polysiloxane chains. The arrangement of the bioactive groups was controlled by the arrangement of the halogenopropyl groups in the bioactive copolymer precursor. All model siloxane copolymers showed high bactericidal activity in a water solution toward the gram‐negative bacteria Escherichia coli and the gram‐positive bacteria Staphylococcus aureus. However, no essential differences in the activities of the copolymers with block and statistical arrangements of units were detected. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2939–2948, 2003

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