J. Chojnowski, L. Wilczek
Jan 5, 1979
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0
Influential Citations
41
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Journal
Macromolecular Chemistry and Physics
Abstract
The polymerization of hexamethylcyclotrisiloxane (D3) was studied in methylene chloride solution in the presence of trifluoromethanesulfonic acid as catalyst. The reaction occurs mostly by addition of monomer to the ends of growing molecular chains. However, an important role is played by cleavage of a siloxane bond in the monomer by acid or water as well as by reverse processes of silanol and/or +ylester end group condensation to siloxane linkages. The latter account for the formation of large amounts of cyclic products and for the coupling of linear chain fragments. They are also responsible for the regeneration of the catalyst leading to establishment of stationary concentrations of reactive species in the polymerization system. The involvement of the above mentioned processes of condensation and siloxane bond cleavage contributes to a dramatic change in kinetics of the polymerization with introduction of water into the reaction system. In particular, the polymerization when carried out without water addition shows three interconnected features: 1 Strong acceleration of the rate with addition of small amounts of water to the system. 2 An apparent negative value of the activation energy. 3 Increase of the rate with decreasing initial concentration of the monomer. Above a certain level of water content the polymerization rate is only slightly dependent on the concentration of water. The energy of activation is 50 kJ/mol and the reaction is of 1st order in monomer, internally as well as externally.