Grafting of Vinyudene Chloride. Model Studies with Poly(Vinyl Alcohol) as Substrate

The modification of coatings resins by graft polymerization of vinylidene chloride should produce a coatings binder with improved barrier properties. For superior color stability, vinylidene chloride must be copolymer-ized with other monomers such as alkyl acrylates and methacrylates. Ceric ion initiation was used to graft vinylidene chloride free-radically onto a model alcohol-containing polymer, polyvinyl alcohol. The effects of various reaction parameters on vinylidene chloride grafting were studied. Graft copolymers were characterized using selective solvent extraction, FTIR, SEM, XES, DSC, and x-ray diffraction.     

偏氯乙烯悬浮聚合反应速率模型

通过实验研究了偏氯乙烯悬浮聚合反应动力学,比较了偏氯乙烯与氯乙烯聚合动力学行为的异同.在假定偏氯乙烯聚合反应发生在单体相和液固界面两个区域的基础上,提出了偏氯乙烯沉淀聚合反应速率模型.模型预测的转化率值几乎在全转化率范围内都与本文的偏氯乙烯悬浮聚合实验结果一致.     

Recent Mechanistic and Synthetic Developments in the Chemistry of Transition‐Metal Vinylidene Complexes

Transition‐metal vinylidene complexes are intermediates in a number of synthetically important transformations of alkynes. Underpinning these applications is the ability of various electron‐rich transition‐metal complexes to effectively facilitate the conversion of alkynes into their vinylidene tautomers. Recent experimental and theoretical studies have provided considerable insight into the mechanisms by which this process occurs and they are detailed herein. In particular, it has been demonstrated that different substituents on both the metal and the alkyne may have profound effects on both the kinetic and thermodynamic profiles of the alkyne/vinylidene tautomerisation. An important finding is that internal alkynes may be employed to prepare disubstituted vinylidene complexes under easily accessible conditions. This discovery brings to light a new facet of the potential synthetic applications of transition metal vinylidene complexes.     

聚偏氟乙烯的辐射交联及其交联度的XPS表征

本文首次用XPS研究了聚偏氟乙烯的辐射交联机理,交联度的XPS表征。计算出聚偏氟乙烯的β值为0.7,发现聚偏氟乙烯的辐射交联的溶胶分数与辐照剂量的关系符合我们提出的通式^[1]。用XPS方法求得聚偏氟乙烯的凝胶化剂量为1.59mrad。     

Experimental and computational evidence for gold vinylidenes: generation from terminal alkynes via a bifurcation pathway and facile C-H insertions

Facile cycloisomerization of (2-ethynylphenyl)alkynes is proposed to be promoted synergistically by two molecules of BrettPhosAuNTf(2), affording tricyclic indenes in mostly good yields. A gold vinylidene is most likely generated as one of the reaction intermediates on the basis of both mechanistic studies and theoretical calculations. Different from the well-known Rh, Ru, and W counterparts, this novel gold species is highly reactive and undergoes facile intramolecular C(sp(3))-H insertions as well as O-H and N-H insertions. The formation step for the gold vinylidene is predicted theoretically to be complex with a bifurcated reaction pathway. A pyridine N-oxide acts as a weak base to facilitate the formation of an alkynylgold intermediate, and the bulky BrettPhos ligand in the gold catalyst likely plays a role in sterically steering the reaction toward formation of the gold vinylidene.     

Reactivity of ruthenium vinylidene complexes containing indenyl/dppe ligands and unsaturated bonds at Cδ with trimethylsilyl azide

This study presents a new reaction of cationic vinylidene complexes with Me?SiN? (TMSN?), which yields N-coordinated nitrile complexes 3. Treatment of a ruthenium acetylide precursor containing indenyl and dppe ligands with a series of organic halides produced the corresponding vinylidene complexes 2 in good yield. Further reaction of 2 with TMSN? at room temperature produced N-coordinated ruthenium nitrile complexes 3. Unlike the reaction of cyclopropenylruthenium complexes with TMSN?, which yielded different products depending on the substituent at Cγ, the vinylidene complexes containing unsaturated bonds at Cd yielded similar N-coordinated nitrile complexes. This transformation did not seemingly occur in the reaction of ruthenium vinylidene complexes containing Cp and PPh? ligands with TMSN?. Deprotonation of these vinylidene complexes yielded cyclopropenyl or thermodynamic furylruthenium complexes, depending on the substitute at Cγ. Subsequent reactions of the cyclopropenyl or furylruthenium complexes with TMSN? afforded different products.     

Fluorocyclopropanes. IV. Copolymers of perfluorocyclopropene

Perfluorocyclopropene undergoes free-radical copolymerization with ethylene, isobutylene, cis- and trans-2-butene, vinyl acetate, methyl vinyl ether, vinyl chloride, styrene, acrylonitrile, tetrafluoroethylene, vinyl fluoride, and vinylidene fluoride. The copolymerization proceeds most readily with electron-rich olefins such as methyl vinyl ether (to yield a 1:1 copolymer), but conditions were found to give copolymers with electron-deficient olefins such as tetrafluoroethylene and vinylidene fluoride. Copolymers with methyl vinyl ether, tetrafluoroethylene, vinyl fluoride, and vinylidene fluoride were examined in detail. Evidence is presented that the perfluorocycloproply ring is incorporated intact into the copolymer and can be subsequently isomerized to a perfluoropropenyl unit by heating at 200–300°C.     

New copolymers of vinylidene fluoride

After a brief presentation of the standard non-functionalized copolymers of vinylidene fluoride, the preparation of new functionalized copolymers is described, by copolymerization of vinylidene fluoride, with other fluoromonomers and non-fluorinated monomers including at least one hydroxy or other functional group. The copolymers are analysed by the conventional methods. Examples of formulation show that these new copolymers are able to give coatings applicable outdoors and offering the same excellent durability as PVDF.     

One-Pot Synthesis of High-Strained Metal Vinylidene and Metal Carbyne

A novel one-pot reaction producing a metal vinylidene structure in a five-membered ring by cyclization of a multiyne has been achieved. The ring strain and the high stability of the cyclic metal vinylidene complexes have been analyzed experimentally and computationally. The metal vinylidene unit in a fused-ring complex is unreactive to both nucleophiles and electrophiles. It reacts however at the nearby carbonyl group achieving the unprecedented conversion of metal tributing factors for the aromaticity-driven process has been studied by DFT calculations.     

Degradation of vinylidene chloride/phenylacetylene (VDC/PA) copolymers. Effect of internal unsaturation on poly(vinylidene chloride) stability

The thermal degradation of vinylidene chloride/phenylacetylene copolymers containing small but varying amounts of phenylacetylene has been examined in both the solid phase and in bibenzyl solution. Incorporation of phenylacetylene into the poly(vinylidene chloride) structure greatly facilitates degradative dehydrochlorination. Indeed, the presence of phenylacetylene promotes the formation of polyene segments during the polymerization process so that all the copolymers, even at very low phenylacetylene loading, are tan in color. The decreased stability of polymers containing interal unsaturation arises from an increased rate of initiation for degradative dehydrochlorination. The propagation rate is largely unaffected by the level of unsaturation initially present in the polymer. The ratio of hydrogen chloride to stilbene formed for degradation of these copolymers in bibenzyl solution is approximately 35:1. This suggests that the chlorine atom of the initially-formed radical pair preferentially abstracts an adjacent hydrogen atom rather than interacting with solvent, i.e., the chain-carrying radical pair does not dissociate appreciably as the unzipping dehydrochlorination occurs. Thus random double bonds introduced in a variety of ways may be identified as principal defect sites responsible for the initiation of the degradative dehydrochlorination of poly(vinylidene chloride). Species which promote the degradation of poly(vinylidene chloride) probably do so by facilitating the introduction of random double bonds into the structure.     

Microhardness measurements of poly(methyl methacrylate) and poly(vinylidene fluoride) polyblends

The preparation of polymer blends of poly(methyl methacrylate) and poly(vinylidene fluoride) in different weight percentages is described. Vickers microhardness measurements have been made to study the effects of load and compositional ratio of the two polymers in polyblend. It is observed that poly(vinylidene fluoride) acts as a plasticizer for poly(methyl methacrylate). Evidence of increasing and decreasing strength of polyblends has been obtained for different compositional ratios of the two polymers.     

Transition metal vinylidene complexes as supramolecular building blocks: nucleobase-mediated self-assembly of crystals with hexagonal symmetry

Reaction of the ruthenium half sandwich compound RuCl(eta(5)-C(5)H(5))(PPh(3))(2) with the uracil (Ur) substituted alkyne HC[triple bond, length as m-dash]CUr in the presence of halide scavengers NH(4)X (X = PF(6), BF(4), OTf) results in the formation of the vinylidene complexes [Ru([double bond, length as m-dash]C[double bond, length as m-dash]CHUr)(eta(5)-C(5)H(5))(PPh(3))(2)][X] which crystallize in the hexagonal space group P6(3)/m. The hexagonal symmetry inherent to the system is due to the formation of a hydrogen bonded array mediated by the two sets of donor-acceptor units on the uracil, resulting in the formation of a cyclic "rosette" containing six ruthenium cations. In solution the (1)H and (31)P{(1)H} NMR spectra of the vinylidene complexes are both concentration and temperature dependent, in accord with the presence of monomer-dimer equilibria in which the rate of rotation of the vinylidene group is fast on the NMR timescale in the monomeric species, but slow in the dimers. The isoelectronic molybdenum-containing vinylidene complex [Mo(eta(7)-C(7)H(7))(dppe)([double bond, length as m-dash]C[double bond, length as m-dash]CHUr)][BF(4)] (dppe = 1,2-bis(diphenylphosphino)ethane) has also been prepared, but forms symmetric dimers in the solid state.     

Effect of poly(ethylene glycol) on the dielectric properties of poly(vinylidene fluoride)/BiFeO<Subscript>3</Subscript>/poly(ethylene glycol) composite films for electronic applications

In the present work a series of poly(vinylidene fluoride)/BiFeO₃/poly(ethylene glycol) composite films were prepared by solvent casting method with poly(vinylidene fluoride) as polymer matrix, bismuth ferrite as ceramic filler and poly(ethylene glycol) as binding agent as well as enhancer. The structural analysis of the composite films by X-ray diffraction confirms that the composites have a distorted rhombohedral structure. The micro-structural analysis shows that the use of poly(ethylene glycol)in the composite films enhances the homogeneity as well as compatibility of BiFeO₃ particles within the poly(vinylidene fluoride) matrix. The dielectric and electrical study done by impedance analyzer reveals that with an increase in poly(ethylene glycol) concentration, there is a subsequent increase in dielectric constant as well as AC electrical conductivity. Finally, the ferroelectric behavior of the composite confirms that the ferroelectric properties of the composites are enhanced by the addition of BiFeO₃ with an increase in poly(ethylene glycol) concentrations. These preliminary results give an idea for possible applications of this type of composites in the field of electronic applications.     

A rare eta2-butadienyl complex from an alkyne double insertion with double vinylidene rearrangement

A rare eta2-butadienyl Ir(III) complex with a weak Ir...C bond is formed from 1-alkyne double insertion with the independent double alkyne to vinylidene rearrangement. A reaction intermediate is isolated, and labeling and crossover experiments indicate the intramolecularity of both alkyne to vinylidene rearrangements.     

Morphology Evolution of Poly（vinylidene fluoride） Membranes during Supercritical CO2 Assisted Phase Inversion

A supercritical carbon dioxide（Sc CO2） assisted phase inversion was developed to produce microporous poly（vinylidene fluoride）（PVDF） membranes whose morphology characteristics arise from both liquid-liquid demixing and solid-liquid demixing（crystallization）. This result was confirmed by Fourier transform infrared spectroscopy（FTIR）, from which both α and β crystals were found. As revealed by contact angle experiment, the PVDF membranes prepared via Sc CO2 assisted phase inversion were more hydrophobic compared with the control membrane produced via conventional immersionprecipitation technique. In particular, the sample with 15 wt% PVDF prepared at 45 °C and 13 MPa exhibited a contact angle of 142°, which was mainly caused by the multilevel micro- and nano- structure. The effects of polyethylene glycol（PEG）, polyvinyl pyrrolidone（PVP） and lithium chloride（Li Cl） on the structures and crystal form were investigated. PVP promoted the formation of β phase crystal form, while PEG boosts the evolution of α phase. Li Cl restrained the crystallization degree of PVDF membrane under Sc CO2.     

Unexpected Chemistry from the Homogeneous Thermal Decomposition of Acetylene: An ab initio Study

The formation of the aromatic ring during the formation of polycyclic aromatic hydrocarbons (PAHs) remains controversial and the experimental evidence is still lacking. Moreover, the formation mechanism of benzene from acetylene in the gas phase has also puzzled organic chemists for decades. Here, ab initio molecular dynamics simulations and electronic structure calculations provide compelling evidence for an unexpected competitive reaction pathway in which the aromatic ring is formed through successive additions of vinylidene. Moreover, no collisions cause bond dissociation of the acetylene molecule during the formation of benzene in this work. This study reveals the key role for the vinylidene carbene and determines the lifetime of vinylidene.     

Toward the spectroscopic identification of vinylidene,H2CC

The singlet electronic ground state of vinylidene will be very difficult to observe spectroscopically, as it rapidly tunnels through a small (≈5 kcal mol^?1) barrier to acetylene. Triplet vinylidene should have a much longer lifetime, and several predictions of its properties are reported here. These include the infrared spectrum and a characterization of the allowed ³B₂-³A₂ electronic transition.     

Structure and properties of nanocomposites based on zinc sulfide and poly(vinylidene fluoride)

The structure and properties of nanocomposites based on zinc sulfide and poly(vinylidene fluoride) were studied. The nanocomposite material was prepared by the matrix isolation technique: ZnS nanoparticles are formed by chemical reactions in a poly(vinylidene fluoride) powder of particle size 0.5–1.0 μm.     

Carbonization of polytetrafluoroethylene surface by UV-induced grafting of vinylidene chloride

A method has been developed for modifying the surface layer of polytetrafluoroethylene by incorporation of poly(vinylidene chloride) via UV radiation-initiated graft polymerization of vinylidene chloride from the vapor phase using a PRK-4 mercury lamp. By the subsequent treatment of the composition with aqueous ammonia, dehydrochlorination (carbonization) of the grafted poly(vinylidene chloride) has been performed. The kinetics of UV grafting and the distribution of the carbonized phase in the polytetrafluoroethylene matrix have been studied. A material with the carbonized surface layer of a 10—30 μm thickness and a contact angle of about 57° remaining stable over time has been obtained.     

Activation of metal-acyl oxygen atoms by triflic anhydride: a simple synthetic route to reactive cationic vinylidene complexes

(η⁵-Cyclopentadienyl) (acyl) (carbonyl) (tertiary phosphine) iron complexes react rapidly with trifluoromethanesulfonic acid anhydride to afford cationic vinylidene complexes, via the intermediacy of cationic carbene complexes. Spectroscopic and chemical characterizations of these vinylidene complexes are reported.