Anionische Kopolymerisation einiger cyklischer Polysiloxane

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Abstract
The anionic copolymerization of some cyclic polysiloxanes catalyzed by strong bases was studied. Copolymerizations were carried out with the use of dodecamethylcyclohexasiloxane and tetradecamethylcycloheptasiloxane as M1 and heptamethylvinyl‐cyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane as M2. LiOH, NaOH, and KOH were used as catalysts. The Mayo and Lewis method was applied in evaluating the copolymerization experiments. The values of the monomer reactivity ratios r1 and r2 obtained imply that changes in temperature do not practically affect the entry of cyclic polysiloxanes into the copolymer chain. On the other hand, copolymerization is strongly influenced by the activity of the catalyst. The character of the metal gegenion is shown in the reaction of the catalyst with the monomer in the first elementary step where it affects the equilibrium of the formation of the transition complex. It has presumably no effect on the second elementary step, i.e., the transformation and linearization of the cyclic part of the complex. The electronegative effect of the vinyl substitution on the Si atom of the cyclic tetramer results in an increased electropositivity of Si in the siloxane unit of the monomer and a decresaed electron density on oxygen of the silanolate group. As a result of these electron effects tetramethyltetravinylcyclo‐tetrasiloxane and heptamethylvinylcyclotetrasiloxane are more reactive as monomers than octamethylcyclotetrasiloxane.

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