Preparation of nanocrystalline metal oxides and intermetallic phases by controlled thermolysis of organometallic coordination polymers

Organometallic coordination polymers of the super-Prussian blue type [(Me₃Sn)_nM(CN)₆] (Me=CH₃; n=3, 4; M=Fe, Co, Ru) were subjected to thermolysis in different atmospheres (air, argon, hydrogen/nitrogen). In air, oxides were found: Fe₂O₃/SnO₂ (crystalline and nanocrystalline), Co₂SnO₄ and RuO₂. In argon and in hydrogen, the intermetallic phases FeSn₂, CoSn₂, Ru₃Sn₇ and Fe₃SnC were obtained. A detailed mechanistic study was carried out using thermogravimetry (TG), X-ray diffraction (XRD), X-ray absorption spectroscopy (EXAFS) at Fe, Co, Ru and Sn K-edges, infrared spectroscopy (IR) and elemental analysis. Below 250°C, Me₃SnCN and (CN)₂ are released, whereas above 250°C oxidation or pyrolysis leads to the corresponding oxides or intermetallic phases. Polymeric cyanides containing at least two metals have turned out to be suitable precursors to prepare well-defined oxides and intermetallic phases at comparatively low temperature.     

The medium dependence of the rates of base cleavage of carbon—silicon and—tin bonds

Rates of cleavage of Me₃MR compounds (M = Si, R = m-ClC₆H₄CH₂, p-NO₂C₆H₄CH₂, Ph₂CH, 9-fluorenyl, and 2-benzothienyl; M = Sn, R = m-ClC₆H₄CH₂, Ph₂CH, 2-benzothienyl) have been measured in Me₂SO/MeOH/MeONa, Me₂SO/EtOH/EtONa, and Me₂SO/H₂O/HONMe₄ media containing varying amounts of the hydroxylic component. The variations in the slopes of the log k_rel  H plots are consistent with the view that a water or alcohol molecule provides electrophilic assistance in the rate-determining step for the tin compounds with R = m-ClC₆H₄CH₂ and 2-benzothienyl, while for the silicon compounds, and possibly for the tin compound with R = Ph₂CH, carbanions are liberated in the rate-determining step.     

Acetonitrile-dependent oxyphosphorylation: A mild one-pot synthesis of β-ketophosphonates from alkenyl acids or alkenes

An efficient one-pot synthesis of β-ketophosphonates has been developed, via the reaction of α,β-alkenyl carboxylic acids or alkenes with H-phosphonates and air oxygen, catalyzed by CuSO₄·5H₂O in CH₃CN. CH₃CN plays a decisive role, probably by forming an active oxygen complex [(MeCN)_nCu^II-O-O·].     

Lignin-type, α,β-unsaturated aldehydes of lignin-type in organic solvents

A 1:1 reaction of [HO(CH₂)₃]₃P with 4-hydroxy-3-methoxy-cinnamaldehyde (coniferaldehyde) or 3,5-dimethoxy-4-hydroxycinnamaldehyde (sinapaldehyde) in acetone at room temperature affords phosphonium zwitterions of the type R₃P⁺CH(4-O^?-Ar)CH₂CHO; other phosphines [R = Et, n-Bu, (CH₂)₂CN, and p-Tol] do not react under the same conditions. In alcohols R??OH(D) [R?? = CD₃, Et, (CD₃)₂CD, s-Bu, HOCH₂CH₂], the above phosphines (except the cyano-derivative) and those where R = i-Pr, Cy, Me₂Ph, MePh₂ do react within an equilibrium established between the reactants and the zwitterion-hemiacetal products R₃P⁺CH(4-O^?-Ar)CH₂CH(OH)(OR??) that are formed as a mixture of two diastereomers. The nature of the phosphine and the alcohol affects the equilibrium and the diastereomeric ratio.     

Effects of substitution and terminal groups for liquid-crystallinity enhanced luminescence of disubstituted polyacetylenes carrying chromophoric terphenyl pendants

Liquid-crystalline and light-emitting poly(2-alkyne)s containing terphenyl cores with hexamethyleneoxy spacers,and cyano or n-propoxy tails -[CH3C=C(CH2)6O-terphenyl-R]n-,where R=CN,CH3PA6CN,R=OCH2CH2CH3,CH3PA6OPr,were synthesized.The effects of the substitution and terminal groups on the properties,especially the mesomorphic and optical properties of the polymers,were investigated.The disubstituted acetylene monomers (CH3A6CN,CH3A6OPr) were pre- pared through multistep reaction routes and were polymerized by WCl6-Ph4Sn in good yields (up to 82%).All the monomers and CH3PA6CN exhibited the enantiotropic SmA phase with a monolayer arrangement at elevated temperatures,whereas CH3PA6OPr formed a bilayer SmAd packing arrangement.Upon excitation at 330 nm,strong UV and blue emission peaks at 362 and 411 nm were observed in CH3PA6OPr and CH3PA6CN,respectively.The luminescent properties of CH3PA6CN and CH3PA6OPr have been improved by introducing the methyl substituted group,and the quantum yield of the polymer with cyano tail CH3PA6CN (φ= 74%) was found to be higher than that of CH3PA6OPr (φ= 60%).Compared to polyacety- lene parents,both CH3PA6OPr and CH3PA6CN showed a narrower energy gap.This demonstrated that the electrical con- ductivities of polyacetylenes could be enhanced by attaching appropriate pendants to the conjugated polyene backbones.     

Functionalization and further crosslinking of the nicalon polycarbosilane based on its metalation with the n-butyllithium—postassium t-butoxide reagent

Reaction of the Nicalon polycarbosilane with the n-BuLi/Me₃COK reagent resulted in metalation of approximately one CH₂ group in four. Reaction of the metalated polymer with Me₂ (CH₂ = CH)SiCl gave a Me₂(CH₂ = CH)Si-substitued Nicalon polycarbosilane. The polymer was heated with different amounts of the [(MeSiH)_～0.8(MeSi)_～0.2]_n polysilane in the presence of azobisisobutyronitrile in refluxing benezene. Hydrosilylation by the Si? H-containing polysilane of the CH₂?CH groups of the Me₂(CH₂?CH) Si-substituted Nicalon polycarbosilane gave a new hybrid polymer (when appropriate quantities of reactant polymers were used) whose pyrolyis in a stream of argon to 1000°C left a ceramic residue in 77% yield whose elemental analysis indicated a nominal composition of 91% by weight SiC and 9% C.     

Stepwise thermal degradation of a polybenzimidazole foam

The stepwise thermal degradation of a polybenzimidazole (PBI) foam, prepared from 3,3′-diaminobenzidine and isophthaldiamide, has been studied under conditions of pyrolysis and nonflaming oxidative degradation in a thermal analyzer using gas and liquid chromatographic separation and mass spectrometric and infrared detection techniques. The recoveries of sample weight, as degradation products, were quantitative over the entire temperature ranges studied (100–300, 300–570, 570–700, and 700–1000°C for pyrolysis; and 100–570 and 570–900°C for nonflaming oxidation). In pyrolysis, 17 volatile compounds were identified with NH₃ and CH₄ accounting for 94 and 57 mole % of the total mass loss between 300–570 and 570–700°C, respectively. Above 700°C, HCN and H₂ were formed from degradation of arylnitrile-containing oligomers. The thermal and oxidative degradation of three substituted benzimidazole monomers was also studied, and the relative ratios of N₂, NH₃, and HCN that were produced from each, when compared with PBI, support a mechanism for degradation that favors cleavages that least alter the conjugation of the polymer backbone. In the presence of air, PBI formed stable oxygen-containing residues that decomposed at high temperatures to N₂, CO₂, and H₂O almost exclusively. Large quantities of H₂ and N₂ from model compounds support results from PBI that suggest that degradation begins with total erosion of the imide ring at 570°C and the formation of more condensed heterocyclic species. These quantitative techniques are generally applicable to the study of all polymeric materials.     

Direct synthesis of CdS nanoparticles via simple one-pot calcination of new two-dimensional Cd(II) coordination polymer

Assembly of quinoxaline with Cd(II) in the presence of SCN^? anion produces a new coordination polymer [Cd(Quinoxaline)(SCN)₂(CH₃CN)] _n [Cd(Quinoxaline)₂(SCN)₂] _n (1) and is characterized by IR, ¹H NMR and ¹³C NMR spectroscopy. The single-crystal X-ray data of compound 1 show that this coordination polymer grows in two-dimensional supramolecular structure. In this polymer, the organic ligand chelate through its one nitrogen atom to cadmium(II) atom and thiocyanate anion acts as a bridge to two cadmium(II) atom in the chains. Also, nanoscale of CdS has been synthesized by calcination at 400, 500 and 600 °C under air atmosphere and characterized by scanning electron microscopy, X-ray powder diffraction and energy-dispersive X-ray. The thermal stability of compound 1 was studied by thermal gravimetric and differential thermal analyses.     

Jahn-teller effects in the MNDO approximation: structures of the molecular cations of some simple organoberyllium compounds

The MNDO method gives geometries for the molecular cations of organoberyllium compounds of types BeR₂ and HBeR (R = CH₃, CHCH₂, CCH, CN, C₅H₅), of C₄H₄Be and CH₃BeBeH₃ and of the series CH_4?n(BeH)_n (n = 0–4) which have symmetries in precise accord with the predictions of the Jahn-Teller theorem. In the series CH_4?n(BeH)_n and CH_4?n(BeH)_n⁺, the barriers to inversion via a planar intermediate decrease with increasing n, are significantly smaller for the cations than for the neutral molecules, and are zero for CH(BeH)₃⁺ and C(BeH)₄⁺, both of which have their minimum energy when strictly planar at carbon.     

An ESR study of PMMA mechanoradicals and of their interaction with oxygen

Analysis of ESR spectra of mechanoradicals from poly(methyl methacrylate) reveals that after mechanical degradation in vacuo at 77°K, the sample contains two types of primary radicals? CH₂? C(CH₃)(COOCH₃) (I) and CH₂? C(CH₃)(COOCH₃)? CH₂ (II) produced by the breaking of the polymer chain, and secondary radicals ? CH₂? C(CH₃)(COOCH₃)? CH? C(CH₃)? (COOCH₃)? CH₂? (III). With increasing temperature, radical I remains stable while II reacts with methylene hydrogen of the polymer chain giving rise to the secondary radical III, which decays and finally disappears as the temperature rises. After admission of oxygen at 113°K, the polymer radicals react with oxygen with formation of polymer peroxy radicals ROO. and diamagnetic dimers. With increasing temperature the latter dissociate again to the original polymer peroxy radicals which gradually decay, if the temperature is increased further. The present results are compared with earlier ones obtained on poly(ethylene glycol methacrylate) (PGMA).     

Synthesis of comb‐type polycarbosilanes via nucleophilic substitution reactions on the main‐chain silicon atoms

A series of comb‐type polycarbosilanes of the type [Si(CH₃)(OR)CH₂]_n {where R = (CH₂)_mR′, R′ = ? O‐p‐biphenyl? X [X = H (m = 3, 6, 8, or 11) or CN (m = 11)], and R′ = (CF₂)₇CF₃ (m = 4)} were prepared from poly(chloromethylsilylenemethylene) by reactions with the respective hydroxy‐terminated side chains in the presence of triethylamine. The product side‐chain polymers were typically greater than 90% substituted and, for R′ = ? O‐p‐biphenyl? X derivatives, they exhibited phase transitions between 27 and 150 °C involving both crystalline and liquid‐crystalline phases. The introduction of the polar p‐CN substituent to the biphenyl mesogen resulted in a substantial increase in both the isotropization temperature and the liquid‐crystalline phase range with respect to the corresponding unsubstituted biphenyl derivative. For R = (CH₂)₁₁? O‐biphenyl side chains, an analogous side‐chain liquid‐crystalline (SCLC) polysiloxane derivative of the type [Si(CH₃)(O(CH₂)₁₁? O‐biphenyl)O]_n was prepared by means of a catalytic dehydrogenation reaction. In contrast to the polycarbosilane bearing the same side chain, this polymer did not exhibit any liquid‐crystalline phases but melted directly from a crystalline phase to an isotropic liquid at 94 °C. Similar behavior was observed for the polycarbosilane with a fluorocarbon chain, for which a single transition from a crystalline phase to an isotropic liquid was observed at ?0.7 °C. The molecular structures of these polymers were characterized by means of gel permeation chromatography and high‐resolution NMR studies, and the crystalline and liquid‐crystalline phases of the SCLC polymers were identified by differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 984–997, 2003     

Metallation studies of organofunctional trisiloxanes

Summary The organofunctional trisiloxanes Me₃SiOSiMe(R)OSiMe₃ [R=(CH₂)₂PPh₂, (CH₂)₃C₅H₄N, (CH₂)₃CN, (CH₂)₂Ph, (CH₂)₂SPh, CH=CH₂ and CH₂CH=CH₂] have been reacted with metal halide and-carbonyl moieties in order to determine the coordination preferences of materials being used as models for metallated longchain linear functionalised polysiloxanes. The products [Me₃SiOSiMe(R)OSiMe₃]₃ML_n [R=(CH₂)₂PPh₂, ML_n=RhCl],cis-[Me₃SiOSiMe(R)OSiMe₃]₂ML_n [R=(CH₂)₂PPh₂ or (CH₂)₃C₅H₄N, ML_n=Mo(CO)₄],trans-[Me₃SiOSiMe(R)OSiMe₃]₂ML_n[R=(CH₂)₂PPh₂, ML_n=NiCl₂, PdCl₂, PtCl₂ and [Rh(CO)Cl] and [Me₃SiOSiMe(R)OSiMe₃]ML_n [R=(CH₂)₂PPh₂, ML_n=Mo(CO)₃(2,2-bipyridine); R=(CH₂)₂Ph, ML_n=Mo(CO)₃; R=(CH₂)₃C₅H₄N, (CH₂)₃CN, or (CH₂)₂SPh, ML_n=Rh(CO)₂Cl; R=CH=CH₂ or CH₂CH=CH₂, ML_n=Fe(CO)₄] have been isolated and characterised spectroscopically in the course of these studies.     

Allycyanide gauche revisited

The microwave spectrum of the ground state of the gauche rotamer of allylcyanide (CH₂=CHCH₂ CN) has been remeasured. The obtained rotational constants A = 19 707.9 ± 0.1, B = 2 619.74 ± 0.05 and C = 2 497.43 ± 0.05 (in MHz) were in good agreement with a structural model. The dipole moment components were also fitted as |μ_a| = 3.50 ± 0.05, |μ_b| = 1.70 ± 0.02 and |μ_c| = 0.19 ± 0.04 (in Debye). The results are in both cases in good agreement with a CCCC dihedral angle near the expected 120°.     

Effects of Chain Ends on Thermal and Mechanical Properties and Recyclability of Poly(γ-butyrolactone)

This work investigates effects of poly(γ-butyrolactone) (PγBL) with different initiation and termination chain ends on five types of materials properties, including thermal stability, thermal transitions, thermal recyclability, hydrolytic degradation, and dynamic mechanical behavior. Four different chain-end-capped polymers with similar molecular weights, BnO-[C(=O)(CH₂)₃O]_n-R, R = C(=O)Me, C(=O)CH=CH₂, C(=O)Ph, and SiMe₂CMe₃, along with a series of uncapped polymers R′O-[C(=O)(CH₂)₃O]_n-H (R′ = Bn, Ph₂CHCH₂) with M_n ranging from low (4.95 kg mol⁻¹) to high (83.2 kg mol⁻¹), have been synthesized. The termination chain end R showed a large effect on polymer decomposition temperature and hydrolytic degradation, relative to H. Overall, for those properties sensitive to the chain ends, chain-end capping renders R-protected linear PγBL behaving much like cyclic PγBL. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2271–2279     

Thermal degradation and evolved gas analysis of N,N′-bis(2 hydroxyethyl) linseed amide (BHLA) during pyrolysis and combustion

The thermal degradation of N,N′-bis(2 hydroxyethyl) linseed amide (BHLA) was investigated by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy and mass spectroscopy (TG–FTIR–MS). Thermogravimetric analysis revealed that the thermal degradation process can be subdivided into three stages: sample drying (<200 °C), main decomposition (200–500 °C), and further cracking (>500 °C) of the polymer. The compound reached almost 800 °C during pyrolysis and combustion. The activation energy at the second step during combustion was slightly higher than that of pyrolysis emissions of carbon dioxide, aliphatic hydrocarbons, carbon monoxide, and hydrogen cyanide, and other gases during combustion and pyrolysis were detected by FTIR and MS spectra. It was observed that the intensities of CO₂, CO, HCN, and H₂O were very high when compared with their intensities during pyrolysis, and this was attributed to the oxidation of the decomposition product.     

Allylbutyltin halides (CH2CHCH2)SnBu3−nCln (n = 0, 1, 2, 3). Preparation,carbon-13 NMR characterization and allylstannylation ability towards ketones and aldehydes

Mixed allylbutyltin halides (CH₂CHCH₂)SnBu_3-nCl_n (n = 0–3) have been prepared, and characterized by carbon-13 NMR spectroscopy. Their ability to bring about allylstannylation of ketones and aldehydes, to form organostannoxy compounds, Bu_3-nSnCl_nOC(R′)(R″)CH₂CHCH₂, has been shown to increase on increasing the value of n, that is on increasing the acceptor ability of the tin centre.     

Novel analytical method for determination of contents of backbone and terminal/branch vinyl acetate groups of poly(ethylene-co-vinyl acetate) using deacetylation reaction

Vinyl acetate (VA) groups in poly(ethylene-co-vinyl acetate) (EVA) exist in backbone, terminal, and branch positions. The VA moieties were converted to carbon-carbon double bonds (∼CH=CH∼) by deacetylation reaction. By deacetylation, the backbone VA group was converted to 1,4-unit (∼CH₂CH=CHCH₂∼) while the terminal and branch ones were converted to 1,2-unit (∼CH=CH₂). A novel analytical method for determination of ratio of backbone and terminal/branch VA contents was developed using off-line pyrolysis and transmission-Fourier transform infrared spectroscopy (FTIR). The analytical method included sample preparation of deacetylated EVA coated on NaCl window for transmission-FTIR analysis and calculation of backbone and terminal/branch VA contents using quantitative analysis of 1,4- and 1,2-units of the deacetylated EVA. Influence of deacetylation conditions (pyrolysis temperatures and times) on degree of deacetylation and other side reactions was also investigated, and proper deacetylation condition was suggested. From the experimental results, proper off-line pyrolysis condition of EVA coated on NaCl window was 300 °C for 60–80 min. The novel analytical method was reliable with the experimental error of below 5%.     

High intrinsic conductivity in ladder type polymers: Pyrolyzed BBB

Through electrical conductivity and ESR measurements of heat treated BBB-rigid-rod ladder polymers, we provide evidence for the existence of an irreversible transformation to another cross-linked ladder polymer with high intrinsic conductivity. The transformation occurs at a pyrolysis temperature, T_p ? 680°C. The results suggest a novel transport mechanism.     

High-frequency permittivity of nitriles of the series CH3(CH2)nCN

The propionitrile polarization characteristics at 20°C were calculated. The deformation molar polarization and permittivity of nitriles CH₃(CH₂) _n CN (n = 0, 1, 2, …) were determined.     

A thermodynamic study of the protonation of some sulphur-containing α,ω-diamines in aqueous solution

The protonation equilibria in aqueous solution of α,ω-thiadiamines of general formula (R)(R′)N(CH₂)_n,S(CH₂)_mNH₂ (R,R′= CH₃ or H) have been investigated potentiometrically and calorimetrically at 25° C in 0.5 mole dm^?3 KNO₃ solution. The enthalpy and entropy changes are discussed in terms of intrinsic proton affinities and solvation effects.