The mechanism of the photochemical degradation of poly(di-n-alkylsilanes) in solution

Karatsu, Takashi; Miller, Robert D.; Sooriyakumaran, Ratnasabapathy; Michl, Josef

doi:10.1021/ja00185a060

Cited by 68 publications

(26 citation statements)

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“…Some hints as to the nature of the conical intersections responsible for the prevalent S 1 -S 0 radiationless decay are offered by observations of photochemical products 6,19 . (i) In a chain abridgement process, a dialkylsilylene is extruded, a new Si-Si bond is formed, and the silicon backbone is shortened by one Si atom.…”

Section: Electronic Excitation In Saturated Moleculesmentioning

confidence: 99%

Why do disilanes fail to fluoresce?

MacLeod

Michl

2011

Collect. Czech. Chem. Commun.

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In contrast to longer peralkylated oligosilanes, many of which fluoresce efficiently, disilanes and trisilanes exhibit no detectable fluorescence even at low temperatures. This is especially striking in the case of disilanes, whose S 1 -S 0 transition is quite strongly allowed, and which must have very efficient electronic excited state deactivation mechanisms. To identify them, we examine the lowest excited singlet state potential energy surface S 1 of Si 2 Me 6 with TDDFT (B3LYP/TZVP, PBE0/TZVP and BHLYP/TZVP) and ab initio (RICC2/TZVP and RIADC(2)/TZVP) methods and identify several shallow minima and nearby funnels. Relaxed excited state structures show strong valence rehybridization relative to the ground state, allowing optimal accomodation of the simultaneous presence of a negative and a positive charge in their Lewis structures. Efficient decay pathways and relations to longer oligosilanes are discussed.

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Section: Electronic Excitation In Saturated Moleculesmentioning

confidence: 99%

Why do disilanes fail to fluoresce?

MacLeod

Michl

2011

Collect. Czech. Chem. Commun.

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“…Production of dimethylsilylene by cleavage of SiOSi bond is the initial step in the reaction mechanism shown for the synthesis of polycarbosilane from PDMS by Yajima et al 9 The major reactions in photodegradation by UV light are homolysis to give silyl radicals and elimination of dimethylsilylene. 13,15,17,18 Since dimethylsilylene (monomer unit) is unstable, the first main peak (M) in the pyrogram can be assigned to be the product derived from it. The THERMAL DEGRADATION OF PDMS AND PTMDSSdimer unit tetramethyldisilene is also unstable and the second peak (D) is assigned to be the product derived from it.…”

Section: Pyrolysis Gc Studiesmentioning

confidence: 99%

“…10,11 Thermogravimetry of PDMS has been reported. 9 Although there have been several studies on photodegradation of permethylated linear and cyclic polysilanes, [12][13][14][15][16][17][18] literature shows no detailed studies on thermal degradation of PDMS. Pyrolysis of PDMS may produce cyclic oligomers as major products, similar to the pyrolysis behavior of polydimethylsiloxane reported earlier.…”

Section: Introductionmentioning

confidence: 99%

Thermal degradation of poly(dimethylsilylene) and poly(tetramethyldisilylene‐co‐styrene)

Radhakrishnan

2005

J of Applied Polymer Sci

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Thermal degradation of poly(dimethylsilylene) homopolymer (PDMS) and poly(tetramethyldisilylene-co-styrene) copolymer (PTMDSS) was investigated by pyrolysis-gas chromatography and thermogravimetry (TG). PDMS decomposes by depolymerization, producing linear and cyclic oligomeric products, whereas PTMDSS decomposes by random degradation along the chain resulting in each monomeric product and various other combination products. The homopolymer was found to be much less stable than the copolymer. The decomposition mechanisms leading to the formation of various products are shown. The kinetic parameters of thermal degradation were evaluated by different integral methods using TG data. The activation energies of decomposition (E) for the homopolymer and the copolymer are found to be 122 and 181 kJ/mol, respectively, and the corresponding values of order of reaction are 1 and 1.5. The observed difference in the thermal stability and the values of the kinetic parameters for decomposition of these polymers are explained in relation with the mechanism of decomposition.

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“…46 Furthermore, silyl radicals are clearly intermediates in the exhaustive photodecomposition of silane high polymers 4 7 -49 and on the basis of isotopic labeling studies, silyl radical disproportionation reactions have been proposed as the primary source of SiH containing oligomers at room temperature. 49 The case for propagating anions in the Wurtz-type polymerization seems somewhat better developed. First, there are substantial solvent effects observed in the presence of dipolar solvents or cation complexing species such as crown ethers and cryptands.…”

Section: Discussionmentioning

confidence: 99%

Low Temperature Wurtz-Type Polymerization of Substituted Dichlorosilanes

Miller

Ginsburg

Thompson

1993

Polym J

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ABSTRACT:We have studied the heterogeneous Wurtz-type polymerization of a number of substituted dichlorosilanes at low temperatures as a function of solvent, metal reductant, reaction temperature, reagent stoichiometry, and additives. At 65°C, aryl dichlorosilanes rapidly produce polymer while dialkyl substituted monomers do not in the absence of additives. While the rate of polymerization of the former is relatively insensitive to steric effects, it is greatly reduced by the presence of electron donating substituents. Reaction temperature is an important variable with higher temperatures producing lower yields of multimodal products. At 65°C substituted dichlorosilanes produce high molecular weight products at low monomer conversions independent of reagent stoichiometry in a manner more consistent with a chain growth process. Polymerization in the presence of potential hydrogen donating solvents and additives produced no evidence for hydrogen atom chain transfer which would be expected if trappable silyl radicals are intermediates. The evidence is more consistent with silyl anions rather than silyl radicals as the propagating species in the heterogeneous polymerization.

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The mechanism of the photochemical degradation of poly(di-n-alkylsilanes) in solution

Cited by 68 publications

References 1 publication

Why do disilanes fail to fluoresce?

Why do disilanes fail to fluoresce?

Thermal degradation of poly(dimethylsilylene) and poly(tetramethyldisilylene‐co‐styrene)

Low Temperature Wurtz-Type Polymerization of Substituted Dichlorosilanes

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