Polysiloxane depolymerization with dimethyl carbonate using alkali metal halide catalysts

Masaki Okamoto, Sumiko Suzuki, Eiichi Suzuki

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Polydimethylsiloxane terminated by a methyl group was almost completely depolymerized in the mixture of dimethyl carbonate (DMC) and methanol using alkali metal halide catalysts to form dimethoxydimethylsilane (DMDMS) and methoxytrimethylsilane (MTMS) monomers. The various alkali metal halides tested as catalysts gave the same monomer yield. The depolymerization rate depended on the kind of alcohol but not on dialkyl carbonate. The results indicate that the siloxane bond is cleaved by methanol attack to form the corresponding monomers together with water and that dimethyl carbonate reacts with water formed as a byproduct to give methanol, whose amount is the same as that of the methanol consumed for cleavage of siloxane bonds. Therefore, dimethyl carbonate, not methanol, acts as the depolymerization reagent in the apparent reaction. Depolymerization of poly(methylphenylsiloxane-ran-dimethylsiloxane) and poly(methylvinylsiloxane-ran-dimethylsiloxane) with dimethyl carbonate in methanol using potassium fluoride catalyst also proceeded to obtain dimethoxymethylphenylsilane and dimethoxymethylvinylsilane, respectively, together with dimethoxydimethylsilane and methoxytrimethylsilane from polydimethylsiloxane parts. Silicone rubber containing silica as an additive was also depolymerized to form dimethoxydimethylsilane together with a small amount of tetramethoxysilane formed from silica additive. Therefore, the depolymerization with DMC using alkali metal salt catalyst can be counted on for recycling silicone waste.

Original languageEnglish
Pages (from-to)239-245
Number of pages7
JournalApplied Catalysis A: General
Volume261
Issue number2
DOIs
Publication statusPublished - 2004 Apr 30
Externally publishedYes

Fingerprint

Siloxanes
Alkali Metals
Metal halides
Depolymerization
Alkali metals
Silicones
Methanol
Carbonates
Catalysts
Monomers
Polydimethylsiloxane
Silicon Dioxide
Silica
Dimethylpolysiloxanes
Silicone Elastomers
Water
Byproducts
Potassium
methyl carbonate
Recycling

Keywords

  • Depolymerization
  • Dimethyl carbonate
  • Polysiloxane
  • Recycling
  • Silicone

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

Cite this

Polysiloxane depolymerization with dimethyl carbonate using alkali metal halide catalysts. / Okamoto, Masaki; Suzuki, Sumiko; Suzuki, Eiichi.

In: Applied Catalysis A: General, Vol. 261, No. 2, 30.04.2004, p. 239-245.

Research output: Contribution to journalArticle

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N2 - Polydimethylsiloxane terminated by a methyl group was almost completely depolymerized in the mixture of dimethyl carbonate (DMC) and methanol using alkali metal halide catalysts to form dimethoxydimethylsilane (DMDMS) and methoxytrimethylsilane (MTMS) monomers. The various alkali metal halides tested as catalysts gave the same monomer yield. The depolymerization rate depended on the kind of alcohol but not on dialkyl carbonate. The results indicate that the siloxane bond is cleaved by methanol attack to form the corresponding monomers together with water and that dimethyl carbonate reacts with water formed as a byproduct to give methanol, whose amount is the same as that of the methanol consumed for cleavage of siloxane bonds. Therefore, dimethyl carbonate, not methanol, acts as the depolymerization reagent in the apparent reaction. Depolymerization of poly(methylphenylsiloxane-ran-dimethylsiloxane) and poly(methylvinylsiloxane-ran-dimethylsiloxane) with dimethyl carbonate in methanol using potassium fluoride catalyst also proceeded to obtain dimethoxymethylphenylsilane and dimethoxymethylvinylsilane, respectively, together with dimethoxydimethylsilane and methoxytrimethylsilane from polydimethylsiloxane parts. Silicone rubber containing silica as an additive was also depolymerized to form dimethoxydimethylsilane together with a small amount of tetramethoxysilane formed from silica additive. Therefore, the depolymerization with DMC using alkali metal salt catalyst can be counted on for recycling silicone waste.

AB - Polydimethylsiloxane terminated by a methyl group was almost completely depolymerized in the mixture of dimethyl carbonate (DMC) and methanol using alkali metal halide catalysts to form dimethoxydimethylsilane (DMDMS) and methoxytrimethylsilane (MTMS) monomers. The various alkali metal halides tested as catalysts gave the same monomer yield. The depolymerization rate depended on the kind of alcohol but not on dialkyl carbonate. The results indicate that the siloxane bond is cleaved by methanol attack to form the corresponding monomers together with water and that dimethyl carbonate reacts with water formed as a byproduct to give methanol, whose amount is the same as that of the methanol consumed for cleavage of siloxane bonds. Therefore, dimethyl carbonate, not methanol, acts as the depolymerization reagent in the apparent reaction. Depolymerization of poly(methylphenylsiloxane-ran-dimethylsiloxane) and poly(methylvinylsiloxane-ran-dimethylsiloxane) with dimethyl carbonate in methanol using potassium fluoride catalyst also proceeded to obtain dimethoxymethylphenylsilane and dimethoxymethylvinylsilane, respectively, together with dimethoxydimethylsilane and methoxytrimethylsilane from polydimethylsiloxane parts. Silicone rubber containing silica as an additive was also depolymerized to form dimethoxydimethylsilane together with a small amount of tetramethoxysilane formed from silica additive. Therefore, the depolymerization with DMC using alkali metal salt catalyst can be counted on for recycling silicone waste.

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