Martel Zeldin

Thermal decomposition of poly(tetramethyloxydisilaethylene)

Thermal decomposition of poly[oxybis(dimethylsilylene)] having chains terminated with trimethylsiloxy groups was studied by thermogravimetry, pyrolysis-mass spectrometry, and infrared spectroscopy. The polymer is thermally less stable than poly(dimethylsiloxane). Depolymerization occurs at temperatures of 250–350°C, although this process also takes place at lower temperatures. The depolymerization produces cyclic oligomers of general formula [(Me2Si)2O]n, with predominant formation of the oligomern=2. The depolymerization is accompanied by processes which are referred to as restructurization because they change the structure of the polymer backbone. Decomposition may lead also to the formation of branching points. The shape of the thermograms taken under isothermal conditions is in agreement with an unzipping mechanism for depolymerization involving random initiation. Excluding the short initial period of the process, the unzipping is terminated at a restructurization point. A low activation energy points to initiation induced by electron transfer, presumably involving traces of contaminant. At higher temperatures, 350–600°C, loss of organic parts of the polymer takes place along with further restructurization. At higher temperatures the polymer was also found to undergo easily oxygenation of its backbone with atmospheric oxygen, which leads to the formation of siloxane groups.

Synthesis and reactivity of 1-methyl-4-ethynylpyridinium triflate

Abstract 1-Methyl-4-ethynylpyridinium triflate has been prepared by treatment of 4-ethynylpyridine with methyl triflate in methylene chloride. This new active acetylenic monomer trimerized to tris -1,3,5-(1-methylpyridinium-4-yl)benzene triflate when heated in aqueous solution. The new compounds were isolated and characterized.

Synthesis and characterization of pyridinyldisiloxanes and their bis-N-oxides

Abstract 2- ( A ) and 3-dimethylchlorosilylpyridine ( B ) were synthesized by reaction of the corresponding lithiopyridines with dimethyldichlorosilane at −76°C. The products were hydrolyzed in aqueous ammonia at room temperature to give the respective disiloxanes ( C and D ) which are stable, colorless distillable liquids. The dimers were characterized by IR, 1 H NMR and MS. The principal by-products of the syntheses were the bis -substituted derivatives. Additionally, the bis- N -oxide of D was prepared by reaction with m -chloroperoxybenzoic acid and characterized by IR, 1 H NMR and MS.

Synthesis and hydrolysis of fluoropyridinyl containing chlorosilanes

Abstract 2-Fluoro-3-dimethylchlorosilylpyridine (A) and 3-fluoro-4-dimethylchlorosilylpyridine (B) were synthesized from the corresponding fluoro-lithio-pyridines and dimethyldichlorosilane at −76°C. The liquid products were unstable on standing. A and B were hydrolyzed in aqueous ammonia at room temperature to give disiloxanes which are stable crystalline solids. The new compounds were characterized by IR, 1H NMR and MS.

Synthesis, characterization, and catalytic properties of polysiloxanes with pendant 4-(3-pyridinyl)butyl and 4-(1-oxypyridin-3-yl)butyl groups

New silane monomers with the pendant 4-(3-pyridine)butyl group have been synthesized by hydrosilation of 3-(3-butenyl)pyridine with MenSi(OEt)3-nH (n=0, 1) using a platinum catalyst. Only β-addition products were observed. The products were characterized by elemental analysis, infrared,1H- and13C-NMR spectroscopy, and gas chromatography-mass spectrometry. Hydrolysis-polycondensation of the difunctional monomer with a basic catalyst, Me4NOH, gave a mixture of cyclic oligomers, principally cyclic tetramer, and linear homopolymer. Under similar reaction conditions, the trifunctional monomer gave crosslinked material which was soluble in common organic solvents. The linear homopolymer and crosslinked polymer were trimethylsilyl end-blocked with hexamethyldisilazane. The cyclic and end-blocked polymers were characterized by elemental analysis and spectroscopic methods. Molecular weights of the polymers were obtained by end-group analysis using1H-NMR spectral data, size exclusion chromatography, and direct insertion-probe mass spectrometry. The cyclic, linear, and crosslinked materials were N-oxidized withm-chloroperoxybenzoic acid and characterized by spectroscopic methods. The polymeric N-oxide derivatives were shown to be effective transacylation catalysts in the synthesis of mixed carboxylic acid anhydrides in immiscible solvents (H2O/CH2Cl2) under phase-transfer conditions. The implications of the results on the mechanism of catalysis are discussed.

Synthesis and Characterization of 3-Pyridinyl Substituted Ethoxysilane Monomers

Abstract Three methods for the synthesis of silane monomers containing 3-pyridinyl and ethoxy groups have been explored: (a) reaction of 3-lithiopyridine (1) with chlorosilanes followed by ethanolysis; (b) reaction of 1 with MeSi(OEt)3-nCln (n = 0, 1); and (c) reaction of 3-bromopyridine with magnesium and MeSi(OEt)3. Method (a) involved several reaction steps, gave low product yields, and entailed the handling and transfer of highly moisture sensitive intermediates. Method (b) gave the best yield of mono-substituted product (60%) but was accompanied by di-substitution product (11%). Method (c) was a convenient, one-step/one-pot experiment, which gave a lower yield of mono-substituted product (45%) but without multiple substitution. Six new compounds (3-Py)SiMe2(OEt), 3-PySiMe(OEt)2, 3-PySi(OEt)3, (3-Py)2SiMe2, (3-Py)2SiMe(OEt), and (3-Py)2Si(OEt)2) were prepared and characterized by elemental analysis, and IR, 1H-NMR, 13C-NMR and MS spectrometry.

Kinetics of thermal depolymerization of trimethylsiloxy end-blocked polydimethylsiloxane and polydimethylsiloxane-N-phenylsilazane copolymer

Abstract The thermal degradation of Me 3 SiO end-blocked polydimethylsiloxane (eb-PDMS) and polydimethylsiloxane- N -phenylsilazane (eb-PDMS-NPhSz) copolymer was studied. For both polymers, relative degree of polymerization( DP / DP 0 ) as a function of conversion ( C = 1 − W / W 0 ) data were obtained. For eb-PDMS with three different molecular weights, the results were consistent with a mechanism involving a rate-determining random siloxane bond cleavage initiation step followed by a rapid and complete depropagation of the active fragments evolving volatile cyclic oligomers. Rate constants for initiation were obtained at four temperatures from plots of DP −1 vs. time for eb-PDMS of M n = 6.83 × 10 4 . An Arrhenius activation energy of ∼ and is consistent with a SiOSi scission transition state. The degradation of eb-PDMS-NPhSz appears to follow the same depolymerization process evolving cyclic oligomers. Although DP / DP 0 vs. C data suggest a random cleavage-complete depolymerization mechanism, an Arrhenius plot suggests a more complex degradation mechanism. The role of impurities as degradation catalysts is discussed.

Laser induced decomposition of 3-pyridinyl(trimethyl)-and 3-pyridinyl(triethoxy)silane

The gas-phase thermal decomposition of the title compounds, induced by a cw CO2 laser and photosensitized by SF6, leads to the formation of several volatile carbonaceous products (hydrocarbons and ethers) and oligomeric deposits which contain almost all of the silicon from the parent compounds. These materials consist of a low- and a high-molecular weight component and contain only a small part of the nitrogen incorporated in the pyridinyl group or bonded to oxygen.

Water-soluble polysiloxanes with pendant 1-oxypyridin-3-yl groups

Polysiloxanes with 1-oxypyridin-3-yl groups bonded to silicon were prepared by base-catalyzed hydrolysis-polycondensation of dialkoxy silane monomers. The polymers were characterized by IR,1H-NMR, and13C NMR spectra. Polymers bearing 1-oxypyridin-3-yl functions were soluble in organic solvents like CH2Cl2 or MeOH. The solubility in H2O increased with increase in molecular weight. The distribution coefficient for materials with different molecular weight in a water/CHCl3 mixture is reported. Quasi-elastic light-scattering data indicate that the Stokes diameter for the polymer with molecular weight 9000 increases in the order H2O<MeOH<CH2Cl2. Structural ramifications of the solvent effect are suggested.