Silacyclobutane as 'Carbanion Pump' in Anionic Polymerization.III.Synthesis of Di- and Tri-block Copolymer by 'Diphenylsilacyclobutane-Potassium tert-Butoxide System'

摘要

Efficiency of formation of carbanion from a combination of an alkaline metal tert-butoxide and a silacycle (carbanion pump efficiency) was studied in the presence of diphenylethylene.Combination of a silacyclobu-tane with potassium counter ion was the most effective among the silacycles studied (1:1 molar ratio).Sodium and lithium counter ions gave low efficiency.When 2-times 1,1-diphenylethylene was used,diphenylsilacyclobutane with potassium counter ion was found superior to dimethylsilacyclobutane-potassium,and produced (tert-butoxy)diphenyl-(5,5-diphenylhexyl)silane as the major trapped product of initially formed carbanion.However,(tert-butoxy)diphenyl-propylsilane and diphenylpropylsilanol were also formed as non-trapped products in 1 to 27% depending on the reaction conditions,especially when tetrahydrofuran-hexane (9:1) was used.Hydrogen elimination from initially formed intermediate was suggested.With 4-times diphenylethylene,or reaction in tetrahydrofuran-hexane (1:1),(tert-bu-toxy)(5,5-diphenylhexyl)silane was produced in 95% yield after treatment with methyl iodide,accompanied by only 1-2% (tert-butoxy)diphenylpropylsilane as non-trapped product,and tert-butoxy anion was converted to carbanion in as high as 97% yield.This carbanion pump system was applied in the syntheses of poly(ethylene oxide)-block-poly-styrene,poly(ethylene oxide)-block-polystyrene-block-poly(ethylene oxide),poly(ethylene oxide)-block-poly(methyl methacrylate),and poly(ethylene oxide)-block-poly(methyl methacrylate)-block-poly(ethylene oxide).