Dehydrocoupling Polymerization Research Articles

Synthesis of poly(silyl ether)s via copper-catalyzed dehydrocoupling polymerization

The development of efficient method to prepare poly(silyl ether)s (PSEs) is highly desirable. Herein, an environmentally sustainable copper-catalyzed dehydrocoupling polymerization was developed with good yields and high molecular weight (up to 48,400 of Mn and up to 97% yield). Monomers of different types (AB type or AA and BB type) are suitable to afford PSEs. The PSEs show good thermal stability and low glass-transition temperature.

Cobalt-catalyzed selective dehydrocoupling polymerization of prochiral silanes and diols

As a kind of material possessing thermal stability, biocompatibility and degradability, polysilylethers (PSEs) have potential applications. Different catalytic systems have been developed for the synthesis of PSEs. However, the resulted PSEs have similar structure, which is unfavorable for adjusting its properties. We herein synthesized a series of novel PSEs with pendant SiH groups via cobalt-catalyzed selective dehydrocoupling polymerization. Various diols and prochiral silanes are suitable for this method. This novel PSEs could also be obtained via a Co-catalyzed one-pot two-step process. Furthermore, asymmetric dehydrocoupling polymerization was studied and high-Mn PSE was obtained. After the cleavage of PSE by methyl magnesium iodide, chiral silane was obtained with high yield and moderate enantioselectivity.

Investigating the Microstructure of Poly(cyclosilane) by 29Si Solid-State NMR Spectroscopy and DFT Calculations

Using high-resolution magic angle spinning (MAS) solid-state NMR spectroscopy and density-functional theory (DFT) calculations, we determine the microstructure of the silicon-based functional polymer poly(1,4Si6) arising from the dehydrocoupling polymerization of cyclosilane 1,4Si6. 1H–29Si refocused-INEPT solid-state NMR experiments allow the unambiguous determination of the number of attached protons to a silicon atom for each 29Si NMR signal in 1,4Si6 and poly(1,4Si6). One-dimensional 1H → 29Si cross-polarization MAS (CPMAS) NMR spectra of poly(1,4Si6) show the development of SiH resonances upon polymerization, and peak integration indicates an average degree of polymerization of 20. The 1H → 29Si CPMAS spectrum of poly(1,4Si6) also shows two sets of isotropic signals, suggesting the presence of at least two distinct species. Two-dimensional 29Si dipolar double-quantum–single-quantum and single-quantum–single-quantum homonuclear correlation NMR spectra reveal similar connectivity in the two species, po...

Synthesis of Poly(silyl ethers) via Iridium-Catalyzed Dehydrocoupling Polymerization

Poly(silyl ethers) (PSEs) are promising degradable materials, and the development of an efficient method to produce them from readily available materials is highly desirable. Herein, we present a dehydrocoupling polymerization of AB-type silyl alcohol monomers catalyzed by homogeneous iridium(I) complexes bearing a bisphosphine ligand. A series of PSEs containing aliphatic or aromatic linkers have been synthesized. The PDI of PSEs could be tuned by varying the ligand of iridium/bisphosphine complexes. Moderate to high yields of polymers with number-average molecular weights (Mn) up to 9.27 × 104 were obtained. The PSEs possess good thermal stability and low glass-transition temperature (Tg = −42 to −83 °C).

Metallocene influence on poly(cyclosilane) structure and properties

Poly(cyclosilane)s, conjugated polymers inspired by crystalline silicon, are synthesized by group 4 metallocene-promoted dehydrocoupling polymerization.

Synthesis of a Fragment of Crystalline Silicon: Poly(Cyclosilane)

AbstractWe report a strategic synthesis of poly(cyclosilane), a well‐defined polymer inspired by crystalline silicon. The synthetic strategy relies on the design of a functionalized cyclohexasilane monomer for transition‐metal‐promoted dehydrocoupling polymerization. Our approach takes advantage of the dual function of the phenylsilyl group, which serves a crucial role both in the synthesis of a novel α,ω‐oligosilanyl dianion and as a latent electrophile. We show that the cyclohexasilane monomer prefers a chair conformation. The monomer design ensures enhanced reactivity in transition‐metal‐promoted dehydrocoupling polymerization relative to secondary silanes, such as methylphenylsilane. Comprehensive NMR spectroscopy yields a detailed picture of the polymer end‐group structure and microstructure. Poly(cyclosilane) has red‐shifted optical absorbance relative to the monomer. We synthesize a σ–π hybrid donor–acceptor polymer by catalytic hydrosilylation.

Synthesis of a Fragment of Crystalline Silicon: Poly(Cyclosilane).

We report a strategic synthesis of poly(cyclosilane), a well-defined polymer inspired by crystalline silicon. The synthetic strategy relies on the design of a functionalized cyclohexasilane monomer for transition-metal-promoted dehydrocoupling polymerization. Our approach takes advantage of the dual function of the phenylsilyl group, which serves a crucial role both in the synthesis of a novel α,ω-oligosilanyl dianion and as a latent electrophile. We show that the cyclohexasilane monomer prefers a chair conformation. The monomer design ensures enhanced reactivity in transition-metal-promoted dehydrocoupling polymerization relative to secondary silanes, such as methylphenylsilane. Comprehensive NMR spectroscopy yields a detailed picture of the polymer end-group structure and microstructure. Poly(cyclosilane) has red-shifted optical absorbance relative to the monomer. We synthesize a σ-π hybrid donor-acceptor polymer by catalytic hydrosilylation.

Titanocene and ansa-titanocene complexes bearing 2,6-bis(isopropyl)phenoxide ligand(s). Syntheses, characterization and use in catalytic dehydrocoupling polymerization of phenylsilane

Aryloxychloro and bis(aryloxy) titanocenes of general formula L2TiCl2–x(OAr′)x where L = η5-C5H5 (x = 1 (1) and 2 (2)), L2 = SiMe2(η5-C5H4)2 (x = 1 (3) and 2 (4)), and Ar′ = 2,6-(CHMe2)2C6H3 were prepared by the reaction of corresponding titanocene dichloride with LiOAr′ and characterized by spectroscopic methods and compound 3 by single crystal X-ray diffraction analysis. The bulky aryloxy ligand in 1 and 3 exerts a hindered rotation around the Ti–O bond on the 1H NMR time scale, resulting in its dynamic behavior in CDCl3 solution. Variable temperature NMR measurements proved the rotation barrier in 3 (ΔG‡298 = 13.9 ± 0.3 kcal/mol) to be lower than that in 1 (ΔG‡298 = 14.7 ± 0.2 kcal/mol) as a consequence of the more open titanocene shell in the ansa-structure of 3. The catalytic behavior of complexes 1–4, [(η5-C5H5)2TiCl2] and [{SiMe2(η5-C5H4)2}TiCl2], was examined in dehydrocoupling polymerization of phenylsilane under comparable conditions, showing a remarkable higher activity for the titanocene complexes with regards to the ansa-titanocene ones. The order of catalytic activities 2 ~ 1 > [(η5-C5H5)2TiCl2] >> [{SiMe2(η5-C5H4)2}TiCl2] ~ 3 ~ 4 reveals the aryloxy ligands to have an enhancing effect on activity in the titanocene series.

Precise Synthesis of Poly(silphenylenesiloxane)s with Epoxy Side Functional Groups by Tris(pentafluorophenyl)borane as a Catalyst

1,ω-Dimethylhydroxysilyl, -dimethylhydrosilyl, -dimethylmethoxysilyl -terminated tetramethylsilphenylenesiloxane prepolymers were prepared by sequential palladium-catalyzed dehydrocoupling polymerization of 1,4-bis(dimethylsilyl)benzene with water, reduction with lithium aluminium hydride, and palladium-catalyzed methanolysis. 1,4-Bis[(glycidyl- or cyclohexene oxide-functionalized alkyl)methylhydrosilyl]benzene and methyldimethoxysilanes with the same epoxy groups were synthesized by hydrosilylation of 1,4-bis(methyldihydrosilyl)benzene and methyldimethoxysilane with (terminal olefin-functionalized alkyl) substituted epoxides in the presence of platinum catalyst. 1,4-Bis[(glycidyl- or cyclohexene oxide-functionalized alkyl)methyl(hydroxy or methoxy)silyl]benzenes were obtained by hydrolysis and methanolysis of the hydrosilyl derivatives. Poly(silphenylenesiloxane)s with epoxy side groups were synthesized by hetero-polycondensation of the hydrosilane, hydroxysilane and methoxysilane functional groups in the prepolymer and 1,4-bis[(epoxy-functionalized alkyl)methylsilyl]benzene, or 1,1-dimethoxy(epoxy-functionalized alkyl)methylsilane in the presence of a catalyst. Tris(pentafluorophenyl)borane was found to be an excellent catalyst for the polymerization. Cross-linking a polymer with 1,4-diaminobenzene gave stretchable polymer film by solution cast method.

Synthesis and Optical Properties of Poly(2-substituted-9,9-dipropargylfluorene)s

Poly(9,9-dipropargylfluorene) and poly(2-substituted-9,9-dipropargylfluorene)s (X = Ac, Br, NO2) were prepared by the palladium-catalyzed dehydrocoupling polymerization reaction of 2-substituted-9,9-dipropargylfluorenes. The thermal and optical properties of the polymers have been investigated. The diacetylenic functions in polymer main chain started to be thermally crosslinked in the range of 143–177°C. The photoluminescence spectra of polymers were in the range of 407–410 nm, which are corresponded to the photon energy of 3.05–3.03 eV. The quantum yield of poly(DPF-Br) is the highest value (55.84%), which means probably the contribution of electron-donating character of Bromine at the 2-position of fluorene.

Ion Conductive Characteristics of Alkylborane Type and Boric Ester Type Polymer Electrolytes Derived from Mesitylborane

Alkylborane type and boric ester type polymer electrolytes bearing mesitylboron units were prepared by hydroboration polymerization or dehydrocoupling polymerization using mesitylborane. The obtained well-defined organoboron polymer electrolytes showed ionic conductivities of 3.05 × 10-5−5.22 × 10-6 S/cm at 50 °C in the presence of various lithium salts. The maximum conductivity was observed when LiTFSI was doped to boric ester type polymers. The lithium ion transference number was calculated to be 0.35−0.50, indicating a significant anion trapping effect of the organoboron unit. The alkylborane type polymer exhibited a higher lithium ion transference number due to stronger Lewis acidity of the alkylborane unit. The organoboron polymer electrolytes were subjected to polymer reaction with organolithium reagents in aim of immobilizing the anion to the polymer chain as borate anion. After the reaction with phenyllithium, ionic conductivities of 9.45 × 10-7−8.22 × 10-7S/cm were observed with a lithium ion transference number of 0.78−0.82. When pentafluorophenyllithium or naphthyllithium was employed as an organolithium reagent, the conductivity increased by 1 order of magnitude due to the improved dissociation degree of the lithium borate unit in the presence of electron-withdrawing substituent.

Synthesis and characterization of poly(silphenylenesiloxane)s containing functional side groups, a study to high-temperature elastomer

Poly(silphenylenesiloxane)s containing hydride or vinyl functional side groups were successfully synthesized by deaminative polycondensation of bis(aminosilane)s having the functional groups with monomeric or polymeric bis(silanol). The bis(silanol) prepolymer was prepared by palladium-catalyzed dehydrocoupling polymerization of 1,4-bis(dimethylsilyl)benzene with water. 1H, 13C, and 29Si NMR revealed that the polymers have exactly alternating structure of the starting component units. The poly(silphenylenesiloxane)s containing functional side groups have low Tgs ranging from — 23 to — 40 ˚C, and exhibit good thermal stability in both nitrogen and air atmosphere. For example, the most thermally stable polymer 3b-alt, having vinyl side groups on half silicon atoms, has Tg at —33˚C which is 11˚C lower than that of the all-methyl substituted PTMPS, and shows the highest degradation temperature at 4988C in nitrogen and 5218C in air. The TGA residues at 800˚C are 67% in nitrogen and 54% in air. Isothermal studies revealed 3b-alt only lost 2.5% weight after 5h at 4008C in nitrogen. © 2003 Elsevier Science Ltd. All rights reserved.

Linear and Hyperbranched Poly(silyl ester)s: Synthesis via Cross-Dehydrocoupling-Based Polymerization, Hydrolytic Degradation Properties, and Morphological Analysis by Atomic Force Microscopy

Poly(silyl ester)s with differing compositions and architectures were synthesized via cross-dehydrocoupling polymerizations of AB and AB2 monomers. Three poly(silyl ester)slinear poly(dimethylsilyl benzoate), linear poly(diisopropylsilyl benzoate), and hyperbranched poly(dimethylsilyl benzoate)were synthesized through the dehydrocoupling polymerization of 4-(dimethylsilyl)benzoic acid, 4-(diisopropylsilyl)benzoic acid, and 3,5-bis(dimethylsilyl)benzoic acid, respectively, as 10 M solutions in ethylene glycol diethyl ether in the presence of 0.25 mol % of 10 wt % palladium on activated carbon at 100 °C under argon for 1−3 days. The characterization of each polymer included infrared (IR), 1H NMR, 13C NMR, and 29Si NMR INEPT spectroscopies, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The degree of branching of hyperbranched poly(dimethylsilyl benzoate) was 51%, as determined by 1H NMR spectroscopy, with spectral analysis confirmed throug...

Dehydrocoupling reactions of hydrosilanes with group 4 metallocenes Cp2MY2 (M = Ti, Zr, Hf; Y = F, OPh, NMe2)

Dehydrocoupling polymerization of phenylsilane with group 4 metallocene precatalysts Cp2MY2 (M = Ti, Zr, Hf; Y = F, OPh, NMe2) under comparable conditions has been examined. All nine title metallocenes produced polysilane products which ranged in molecular weight from 1100 to 4400 and exhibited ratios of linear to cyclic products from ~2 to 30. The highest molecular weight polysilanes observed for each metal were obtained from Cp2M(NMe2)2 and the highest percentage of linear polysilane was found with Cp2Hf(NMe2)2. The near stoichiometric reactions of Cp2MY2 with PhSiH3, PhMeSiH2, and Ph2MeSiH were monitored by 1H, 19F and 29Si NMR spectroscopy and in all cases exchange products containing Si-Y were identified. Metal hydride species could be observed only with Cp2TiY2.Key words: metallocene, dehydrocoupling, polymerization, hydrosilanes, polysilane.

New Structures of Preceramic Polysilazanes Synthesized by Transition Metal Catalysis

ABSTRACTFurther capability of silazane dehydrocoupling polymerization catalyzed by ruthenium carbonyl (20–200 ppm) is demonstrated in a series of reactions. Ammonia and monomethylamine are used as reactants to bridge oligomers and polymers containing Si-H bonds to provide higher molecular weight polymers with higher latent reactivity and to increase the ceramic yields and the nitrogen-to-carbon ratio in the final ceramic compositions. New types of tractable polymers containing cyclomers having [MeSiHNH] units with molecular weights over 2000 d are formed. Various polymeric properties (e.g., viscosities, softening and melting points) and ceramic yields up to 80–85 wt% are obtained by controlling the catalytic reaction conditions.