and29Si NMR Research Articles

Synthesis and characterization of poly(1-sila-cis-pent-3-enes) substituted with pendant pyridinyl groups

Poly[1-methyl-1-[3′-(3″-pyridinyl)propyl]-1-sila-cis-pent-3-ene], poly[1-phenyl-1-[3′-(3″-pyridinyl)propyl)-1-sila-cis-pent-3-ene], and poly[1-phenyl-1-(4′-pyridinyl)-1-sila-cis-pent-3-ene] were synthesized by the anionic ring-opening polymerization of 1-methyl-1-[3′-(3″-pyridinyl)propyl]-1-silacyclopent-3-ene, 1-phenyl-1-[3′-(3″-pyridinyl)propyl]-1-silacyclopent-3-ene, and 1-phenyl-1-(4′-pyridinyl)-1-silacyclopent-3-ene, respectively. These are the first polycarbosilanes which contain heterocyclic pyridine units as side-chain substituents. These polymers were characterized by1H,13C, and29Si NMR as well as by IR and UV spectroscopy. The molecular weight distributions were determined by gel permeation chromatography, glass transition temperatures, by differential seanning calorimetry: (DSC) and thermal behavior, by thermogravimetric analysis. (TGA).

Silphenylene and silphenylene-siloxane oligomers: Structure-property relationships

Some representative oligomers were prepared by polycondensation reactions of dimethyldichlorosilane with 1,4-di-Grignard reagent prepared from 1,4-dibromobenzene in diethyl ether. The structural characterization of the oligomers was carried out by FTIR and1H,13C, and29Si NMR spectroscopy. TheMn values were determined by vapor pressure osmometry. TheTg values were measured by DSC and the thermodegradation process was analyzed by TGA. In all cases the oligomers prepared in the absence of the blocking end group showed siloxane units in the main chain, which were quantified by1H and29Si NMR.29Si NMR was also used to determine the oligomer sequence. It was possible to correlate the\(\bar M_n \) and structure withTg and with temperature at 3% weight loss. The results agree with these obtained for structurally similar polymers.

Chemical modification of copoly(methylsilylene/1,4-phenylene) by Pt-catalyzed hydrosilation reactions with functionally substituted alkenes

Copoly(methyl-3′-biphenoxypropylsilylene 1,4-phenylene), copoly(methyl-3′-cyanopropylsilylene 1,4-phenylene), copoly(methyl-3′-ethoxypropylsilylene 1,4-phenylene), copoly(methyl-3′-phenoxypropylsilylene 1,4-phenylene), and copoly(methyl-4′,7′,10′,13′-tetraoxatetradecanylsilylene 1,4-phenylene) have been prepared by platinum-catalyzed hydrosilation graft reactions between poly (methylsilylene 1,4-phenylene) and appropriate functionally substituted alkenes. These polymers have been characterized by1H,13C, and29Si NMR as well as by FT-IR and UV-vis spectroscopy. The molecular weight distribution of these polymers has been determined by gel permeation chromatography (GPC), and their glass transition temperatures (Te) by DSC.

IR and29Si NMR investigation of the influence of alkaline modification on the structure of hydrothermally dealuminated Y zeolites

IR and29Si NMR investigation of the influence of alkaline modification on the structure of hydrothermally dealuminated Y zeolites

IR and29Si NMR investigation of the influence of alkaline modification on the structure of hydro thermally dealuminated Y zeolites

Using IR and29Si NMR spectroscopy the influence of alkaline modification on the structure of samples obtained by steaming the ammoniated form of NH4NaY zeolite (53% NH4+, Si/Al=2.37 pretreated under a moist atmosphere at 873 K) at 973 and 1073 K has been studied. Highly dealuminated forms of faujasite arise in the course of hydrothermal treatment as a result of the transfer of Al from the framework to extraframework hydroxide species accompanied by the formation of silica-type disiloxane bonds. The treatment of highly dealuminated samples with an aqueous solution of KOH at 353 K results in the partial regeneration of the crystallographic positions of Al in the framework. The structure of the sample modified with the alkali is identical to that of silicaalumina gel (Si/Al ≈ 2.2) “aged” in air for a long period of time.

Sol-Gel Synthesis of Protoenstatite

ABSTRACTProtoenstatite, a high-temperature polymorph of enstatite (MgSiO3), is generally not stable at room temperature, and is difficult to synthesize. Using a recently developed, hydrogen peroxide-assisted, sol-gel synthesis, protoenstatite was synthesized in a form that was stable at room temperature. Its crystallization was strongly dependent on processing conditions, particularly on the manner in which the xerogel was formed and fired. Xerogels prepared by evaporation, sprav-drying and freeze-drying were compared by XRD, HTXRD, BET, TG/DTA, and 29Si NMR methods. When samples were prepared by evaporation or spray-drying, the result was a mixture of polymorphs. Only the freeze-dried precursor yielded protoenstatite at a lower temperature and within a shorter time than any previously reported.

Partial and complete hydrogenation of poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene)

Poly(1-methyl-1-phenyl-1-silapentane)(II), andblock copoly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene/1-methyl-1-phenyl-1-silapentane) (block-III) have been prepared by catalytic hydrogenation of poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene)(I) over 5% palladium on carbon. These polymers have been characterized by1H,13C and29Si NMR as well as IR spectroscopy. Molecular weight distributions have been evaluated by gel permeation chromatography (GPC). Thermal stabilities have been measured by thermogravimetric analysis (TGA). Glass transition temperatures (Tg's) have been determined by differential scanning calorimetry (DSC).

Synthesis, characterization, and platinum-catalyzed hydrosilation cross-linking of copoly(methylsilylene/1,4-phenylene/methylvinylsilylene): Properties of aromatic carbosilane thermosets

Low molecular weight copoly(methylsilylene/1,4-phenylene/methylvinylsilylene) (I) has been prepared by the reaction of a mixture of methyldichlorosilane and methylvinyldichlorosilane with the di-Grignard reagent prepared fromp-dibromobenzene.I has been characterized by1H,13C, and29Si NMR as well as FT-IR spectroscopy. Its molecular weight distribution has been determined by gel permeation chromatography (GPC), its thermal stability in nitrogen evaluated by thermogravimetric analysis (TGA), and its glass transition temperature (Tg) measured by differential scanning calorimetry (DSC). Platinum-catalyzed hydrosilation cross-linking ofI yields a thermoset material. The bending modulus (logE′), tan·, andTg of these cross-linked materials have been measured by dynamic mechanical thermal analysis (DMTA). Carbon fabric treated with catalytic amounts of platinum has been coated withI. Multilayers of coated carbon fabric have been consolidated (cured) to yield aromatic carbosilane/carbon composite materials. The interlaminar shear strength of these materials has been determined by short beam shear. Flexure strength and modulus of elasticity of these composite samples have been measured. The ultimate compressive strength and compression modulus as well as the tensile strength and elastic modulus of these have been determined.

Synthesis, characterization, and platinum-catalyzed cross-linking of 1,4-bis(1-methyl-1-silacyclobutyl) benzene, co-oligo(1-silacyclobut-1-ylidene-1,4-phenylene), and co-oligo(1-silacyclobut-1-ylidene-4,4?-diphenylene)

1,4-bis(1-Methyl-1-silacyclobutyl)benzene (I) has been prepared by the reaction of 1-chloro-1-methyl-1-silacyclobutane with the di-Grignard reagent prepared fromp-dibromobenzene. In a similar manner, co-oligo(1-silacyclobut-1-ylidene-1,4-phenylene) (II) and co-oligo(1-silacyclobut-1-ylidene-4,4′-biphenylene) (III) have been prepared by condensation oligomerization between 1,1-dichloro-1-silacyclobutane and the di-Grignard reagents prepared fromp-dibromobenzene and 4,4′-dibromobiphenyl, respectively. These have been characterized by1H,13C, and29Si NMR as well as FT-IR and UV spectroscopy. The molecular weight distributions of these co-oligomers have been determined by GPC. Their thermal stabilities have been evaluated by TGA. Thermal degradation of these co-oligomers in nitrogen gives high (60%) char yields. The stability of these chars in air has been determined. TheTg's of these co-oligomers have been measured by DSC. Platinum-catalyzed ring opening of the silacyclobutane rings ofI,II, andIII cross-links these to thermoset materials. The bending moduli (logE′), tan δ, andTg's of these materials have been determined by DMTA. The dielectric constant and dissipation factor of cross-linkedII are reported.

Chemical transformations of functional polycarbosilanes

The functional polycarbosilane [Si(X2)C2H4] n , whereX2=Cl2 (1), was chemically transformed into the corresponding polymers, whereX2=F2 (3), (2-N, N-dimethylbenzylamino)(H) (5), (9-N,N-dimethyl-1-naphthylamino)(H) (6), (1-C10H7)(H) (7), Me2 (8a), (Me3SiNH)2 (10), and (vinyl)(H) (11). The functional polycarbosilane, whereX2=H2 (2), was converted into the polymers, whereX2=Me(H) (8b) and (OMe)2 (9). Reaction of3 with KF in the presence of 18-crown-6 gave rise to the poycarbosilane4 containing both pentacoordinate and tetracoordinate silicons in the proportion of 1:15 as shown by quantitative19F and29Si NMR. Conversion of a greater proportion of silicon atoms to the pentacoordinate state was not possible because of insolubility of the resulting ionomer in the reaction medium.

Study of trimethylsilylated aerosil by IR and29Si NMR spectroscopy

Study of trimethylsilylated aerosil by IR and29Si NMR spectroscopy

Synthesis of poly[(silanylene)thiophene

Poly[(silanylene)thiopene]s, copolymers with alternating thiophene, 2,2′-bithiophene, or 2,2′:5′,5″-terthiophene and mono-, di-, or tetrasilanylene units, were prepared by condensation of the dilithium salts of the thiophenes or the bis(2′-thienyl)silanes with α,ω-dichlorosilanes in diethylether. The polymers were characterized with1H,13C, and29Si NMR, UV, IR, GPC, TGA, and elemental analyses. UV absorption maxima of these polymers all show a red shift with increasing length of the polymer backbone, suggesting that conjugation occurs through the combined σ-Si and π-thiophene backbone.

Synthesis and characterization of poly(3,4-benzo-1-phenyl-1-silapentene) and poly(3,4-benzo-1-silapentene)

Low molecular weight poly(3,4-benzo-1-phenyl-1-silapentene) (I) has been prepared by the anionic ring opening polymerization of 3,4-benzo-1-phenyl-1-silacyclopentene (II), co-catalyzed by methyllithium and HMPA in THF at low temperature. Poly(3,4-benzo-1-silapentene) (III) has been prepared similarly by polymerization of 3,4-benzo-1-silacyclopentene (IV) except that HMPA has NOT been utilized in this latter case. I and III have been characterized by1H,13C, and29Si NMR as well as by IR and UV spectroscopy. The low molecular weight of I and III permits end group analysis by29Si NMR. The molecular weight distributions of I and III have been determined by gel permeation chromatography (GPC) and their thermal stability by thermogravimetric analysis (TGA).

Synthesis of poly(1-methyl-1-phenyl-1-silapentane) by chemical reduction of poly)1-methyl-1-phenyl-1-sila-cis-pent-3-ene with diimide

Poly(1-methyl-1-phenyl-1-silapentane) (I) has been prepared by the chemical reduction of the carbon-carbon double bonds of poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene (cis-II) with diimide, which was generatedin-situ by the thermal decomposition ofp-toluenesulfonhydrazide in refluxing toluene. At lower temperature (100°C),cis-II is isomerized byp-toluenesulfinic acid to lower molecular weight poly(1-methyl-1-phenyl-1-sila-cis andtrans-pent-3-ene) (cis/trans-II). Protodesilation of I with trifluoromethanesulfonic acid yields poly(1-methyl-1-trifluoromethanesulfonyl-1-silapentane) (III). The structures of I andcis/trans-II have been characterized by1H,13C and29Si NMR, GPC, TGA and elemental analysis. The structure of I has been characterized spectroscopically by1H,13C,19F and29Si NMR.

Ring opening metathesis polymerization of 1,1-diphenyl-1-sila-cyclopent-3-ene

1,1-Diphenyl-1-silacyclopent-3-ene (I) has been polymerized by ring opening metathesis using tungsten hexachloride and either cyclopentene or cyclohexene as an initiator, with or without tetraphenyltin as a cocatalyst. The product polymer poly(1,1-diphenyl-1-sila-cis-pent-3-ene) (II) has been characterized by1H,13C, and29Si NMR and IR spectroscopy.

Anions and radicals as intermediates in the reductive coupling of disubstituted dichlorosilanes with sodium

Polymerization of four monomers with alkenyl groups: allylmethyldichlorosilane, allylphenyldichlorosilane, 5-hexenylphenyldichlorosilane and 5-hexenylmethyldichlorosilane was studied by reductive coupling with sodium in the presence of ultrasound at ambient temperatures. Soluble homopolymers and copolymers with phenylmethyldichlorosilane with molecular weights Mn >10,000 were obtained for the first three monomers. UV and29Si NMR studies indicate a high degree of Si-Si catenation for allyl derivatives. Approximately half of the alkenyl groups remain in the polymer after a few hours. This indicates that after the formation of the polysilane backbone alkenyl groups are predominantly trapped intramolecularly in a process resembling cyclopolymerization of diallylsilanes. The main mechanistic conclusion is that in the reductive coupling process radicals are present as short living intermediates which are rapidly reduced to anions at higher polymerization degrees, but which are efficiently trapped at a monomeric or dimeric level. Thus, electron transfer proceeds in two one-electron transfer steps from a chloroterminated chain to a radical, and then to a macromolecular silyl anion. The latter reacts with a monomer via a nucleophilic substitution. Polymerization is an anionic chain growth process.

Reductive silylation of chloroprene

Copolymers made up of 1,4-(2-trimethylsilyl-1,3-butadiene) (I) and 1,4-(2-chloro-1,3-butadiene) (II) units have been prepared by reaction of chloroprene with trimethylchlorosilane and sodium dispersion in THF. The ratio of I∶II units in the copolymers have been determined by IR,1H NMR and elemental analysis. The E∶Z ratio of these units has been determined by1H NMR.13C and29Si NMR of these copolymers is discussed.

Comb polysiloxanes with ?-hydroxyoligo(oxyethylene) side chains

Comb-like polysiloxanes with pendant chains of the type (CH2)3(OCH2 CH2)nOH (n=0, 8 or 15) were synthesized by hydrosilylation of poly(methylsiloxane) with the corresponding monoallyl glycols in which the hydroxyl group was protected with tetrahydropyran. The polymers were characterized by1H and29Si NMR, and by GPC and DSC. A considerable fraction of small cycles is formed for the n=o compound during the deprotection reaction. Side chain crystallization occurs but is slower than for polymers containing side chains with terminal methoxy groups.

Trimethylsilyl derivatives of 2,2-dimethylhydrazides of aromatic acids

Trimethylsilyl derivatives of the dimethylhydrazides of aromatic acids have been prepared.1H,13C, and29Si NMR spectroscopy were used to establish that these derivatives are the dimethylhydrazones of the trimethylsilyl esters of the aromatic acids exclusively in the Z configuration.

Silylotropy and the29Si NMR spectrum of 2-[dimethyl(pentafluorophenyl)siloxy]-2-penten-4-one

1H,13C, and29Si NMR spectroscopy was used to study the structure and silylotropy of 2-[dimethyl(pentafluorophenyl)siloxy]-2-penten-4-one. The temperature dependence of the29Si NMR chemical shifts indicated the existence of an intermediate with pentacoordinated silicon.