Metal ion initiated charge-transfer photopolymerization of tetrahydrofuran. A mechanistic investigation

Michael E. Woodhouse, Frederick D. Lewis, Tobin J Marks

Research output: Contribution to journalArticle

64 Citations (Scopus)

Abstract

Irradiation of dilute solutions of salts of Ag(I), Cu(II), Cu(I), and Tl(I) having suitable noncoordinating anions in tetrahydrofuran results in the formation of polytetrahydrofuran in yields comparable to those for acid-catalyzed (dark) polymerization. The yield of polymer is dependent upon the identity and concentration of metal ion, the anion, the duration of irradiation, and the dark time following irradiation. The observed polymer-yield dependencies upon metal ion and anion at low conversions are Cu(II) > Ag(I) > Cu(I) ≫ Tl(I) and PF6- > SbF6- ≫ OTf- > BF4-. Both the counterion dependence and increase in polymer yield with dark time following photoinitiation are indicative of a cationic ring-opening polymerization process. Initiation of polymerization is proposed to occur via ligand-to-metal charge-transfer excitation of the metal ion-ether complex to generate oxidized ether and reduced metal, which precipitates from solution. The ether cation radical reacts further to form reactive intermediates known to initiate the cationic ring-opening polymerization of tetrahydrofuran. Evidence in support of the proposed mechanism of initiation and polymerization is presented. The initiation of thermal and photochemical ring-opening polymerization of several other ethers by metal salts is also described.

Original languageEnglish
Pages (from-to)5586-5594
Number of pages9
JournalJournal of the American Chemical Society
Volume104
Issue number21
Publication statusPublished - 1982

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Photopolymerization
Ring opening polymerization
Polymerization
Ether
Anions
Metal ions
Charge transfer
Ethers
Polymers
Cationic polymerization
Metals
Irradiation
Ions
Negative ions
Salts
Cations
Precipitates
Ligands
Acids
Positive ions

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Metal ion initiated charge-transfer photopolymerization of tetrahydrofuran. A mechanistic investigation. / Woodhouse, Michael E.; Lewis, Frederick D.; Marks, Tobin J.

In: Journal of the American Chemical Society, Vol. 104, No. 21, 1982, p. 5586-5594.

Research output: Contribution to journalArticle

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AB - Irradiation of dilute solutions of salts of Ag(I), Cu(II), Cu(I), and Tl(I) having suitable noncoordinating anions in tetrahydrofuran results in the formation of polytetrahydrofuran in yields comparable to those for acid-catalyzed (dark) polymerization. The yield of polymer is dependent upon the identity and concentration of metal ion, the anion, the duration of irradiation, and the dark time following irradiation. The observed polymer-yield dependencies upon metal ion and anion at low conversions are Cu(II) > Ag(I) > Cu(I) ≫ Tl(I) and PF6- > SbF6- ≫ OTf- > BF4-. Both the counterion dependence and increase in polymer yield with dark time following photoinitiation are indicative of a cationic ring-opening polymerization process. Initiation of polymerization is proposed to occur via ligand-to-metal charge-transfer excitation of the metal ion-ether complex to generate oxidized ether and reduced metal, which precipitates from solution. The ether cation radical reacts further to form reactive intermediates known to initiate the cationic ring-opening polymerization of tetrahydrofuran. Evidence in support of the proposed mechanism of initiation and polymerization is presented. The initiation of thermal and photochemical ring-opening polymerization of several other ethers by metal salts is also described.

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