Vinylidene Groups Research Articles

High-Field Nuclear Magnetic Resonance Studies Reveal New Structural Landscape of Sulfur-Vulcanized Natural Rubber.

Despite intensive research efforts over the past 3 decades, the structural analysis of sulfur-vulcanized natural rubber (NR) remains challenging owing to the complexity and low population of its sulfur moieties. Herein, solid vulcanized NR samples and NR samples reacted with sulfur and other reactants in an organic solvent were analyzed by solid-state NMR with fast magic-angle spinning and solution NMR, respectively. The present high-field two-dimensional NMR analysis revealed six novel sulfur moieties in these samples, including cyclic sulfides, cyclic di/polysulfides, and crosslinked structures with a vinylidene group. While previous studies reported a variety of sulfur-crosslinked structures in NR, our analysis identified only two dominant types of crosslinked structures that matched those reported previously. Our NMR assignments for the crosslinked structures were inconsistent to a large extent with those presented in the previous studies; thus, in the current work, the crosslinked structures were reassigned using the new data. Based on quantitative NMR analysis, this study also provides the first tangible evidence that cyclic rather than crosslinked sulfides can be the dominant sulfur moieties in vulcanized NR. These results may drastically alter the previously established structural landscape of sulfur-vulcanized NR.

Enhanced Stability and Emission Properties of Perylene Dyes by Surface Tethering: Preparation of Fluorescent Ru Nanoparticle Suspensions by Alkyne Linker Chemistry

Spherical ruthenium nanoparticles (NPs) with a narrow size distribution were synthesised in ethanol by a facile low-temperature solvothermal process without the assistance of templates, structure-directing agents or post annealing/reduction treatments. Surface passivation with a fluorescent perylene dye (EP), and with silane ligands (ETMS), both initially bearing alkyne groups and subsequently forming vinylidene linkages, provided stable suspensions of the marginally soluble free EP. Quantitative analysis of the suspension gave an estimated EP surface coverage of 15 %, corresponding to an EP/ETMS mole ratio of ≈1:6. Photophysical evaluation of the bound and free dye revealed similar absorption bands and extinction coefficients and improved properties for the bound state, including enhanced fluorescence in the visible range for the bound dye, an extended absorption range into the near-UV providing strong emission in the visible, and significantly improved photostability. The physical basis of the enhanced photophysical properties, potential routes to further improvements and the implications for applications are discussed.

Содержание двойных связей в полиэтилене

The content of double bonds in high-pressure polyethylene of various brands obtained from Russian and foreign manufacturers was studied. The essence of the method was to build a calibration curve on an infrared Fourier spectrometer for standard substances with a previously known arrangement of the double bond, saturation of double bonds in the initial polyethylene using gaseous bromine, and subsequent assessment of the locations and number of double bonds in the studied brands of high pressure polyethylene. The calibration substances were trans-4-decene with a purity of 96%, 1-decene with a purity of 95%, and 2-methyl-1-heptene with a purity of 98%. To record infrared spectra, calibration substances were dissolved in carbon disulfide with a purity of 99.5%. The spectra of the calibration substances were recorded in the transmission mode. The recording of the spectra of the high-pressure polyethylene samples was carried out in the reflection mode. To calculate the molar adsorption coefficient of individual calibration substances, the areas of the peak absorption of individual substances were allocated. The Peak Separation NETZSCH software was used for this purpose. For all analyzed samples, both brominated and not brominated, the ratio of the areas of absorption peaks was calculated. For each sample of high-pressure polyethylene, the content of trans-vinylidene, vinyl, and vinylidene groups C=C per 1000 carbon atoms was determined. The total number of double bonds was calculated as the sum of all analyzed bonds contained in the polyethylene sample. The accuracy of the analysis method performed by a single laboratory on a single sample is ±10% of double bonds per 1000 carbon atoms. The technique allows one to evaluate such a characteristic of low density polyethylene as the content of double bonds. This characteristic is essential for the efficient development of crosslinkable polyethylene compounds.

Itaconic acid derivatives: structure, function, biosynthesis, and perspectives

Itaconic acid possessing a vinylidene group, which is mainly produced by fungi, is used as a biobased platform chemical and shows distinctive bioactivities. On the other hand, some fungi and lichens produce itaconic acid derivatives possessing itaconic acid skeleton, and the number of the derivatives is currently more than seventy. Based on the molecular structures, they can be categorized into two groups, alkylitaconic acids and α-methylene-γ-butyrolactones. Interestingly, some itaconic acid derivatives show versatile functions such as antimicrobial, anti-inflammatory, antitumor, and plant growth-regulating activities. The vinylidene group of itaconic acid derivatives likely participates in these functions. It is suggested that α-methylene-γ-butyrolactones are biosynthesized from alkylitaconic acids which are first biosynthesized from acyl-CoA and oxaloacetic acid. Some modifying enzymes such as hydroxylase and dehydratase are likely involved in the further modification after biosynthesis of their precursors. This contributes to the diversity of itaconic acid derivatives. In this review, we summarize their structures, functions, and biosynthetic pathways together with a discussion of a strategy for the industrial use. KEY POINTS: • Itaconic acid derivatives can be categorized into alkylitaconic acids and α-methylene-γ-butyrolactones. • The vinylidene group of itaconic acid derivatives likely participates in their versatile function. • It is suggested that α-methylene-γ-butyrolactones are biosynthesized from alkylitaconic acids which are first synthesized from acyl-CoA and oxaloacetic acid.

IR spectroscopy research of the influence of UV radiation on stabilized polyethylene composites

The paper presents the results of the IR spectroscopy study of the effect of UV radiation on polyethylene composites containing various climatic stabilizers. These composites are used for storage and transportation of hydrocarbon materials to remote areas of the Republic of Sakha (Yakutia), in which where are both large fluctuations in average annual temperature and a high level of solar radiation. It was found that UV radiation affecting the surface of the composites produces radical reactions with the formation of oxidized products, as well as unsaturated bonds. The following products were detected: carboxylic acids, esters, aldehydes, and compounds containing vinylene and vinylidene groups. It was shown that the number of vinyl groups after irradiation decreases. It has been suggested that a high concentration of vinylidene groups may indicate the effectiveness of the stabilizer against UV radiation. From the comparison of the obtained results with the studies of the features of polyethylene aging under UV radiation described by other authors, it was observed that there is a frequency shift corresponding to the fluctuation of the vinylidene group, which may indicate the formation of cyclic structures. Besides, it was shown that the results are in good agreement with the data obtained during long-term climatic tests of similar composites described in a previous publication by the authors.

An outstanding heat-resistant hydroxyl boron–silicone oil with hyperconjugation action in backbone

A high heat-resistant hydroxyl boron–silicone vinylidene oil (HBSVO) was synthesized by copolymerizing hydroxyl polyborosiloxane oil (HPBSO) prepolymer with fumaryl chloride. The temperature at 5% mass loss (T5), 10% mass loss (T10), and maximum decomposition rate (Tmax) of HBSVO was 515, 550, and 600 °C, respectively. The structure –Si–O–B–O–C(=O)–CH=CH–C(=O)– in the backbone of HBSVO might cause a tendency to form a five-member ring structure by hyperconjugation action between boron atom and vinylidene groups. The hyperconjugation action, which improved the heat-resistant and hydrolysis-resistant properties of HBSVO, was confirmed by UV spectroscopy, 11B-NMR, and 1H-NMR. The chemical moieties (–Si–O–B–O–C(=O)–CH=CH–C(=O)–) were also identified by Fourier transform infrared (FT-IR) and 29Si-NMR (CDCl3) spectroscopies.

Functionalized Polyesters with Tunable Degradability Prepared by Controlled Ring-Opening (Co)polymerization of Lactones

Various well-defined diblock copolymers with poly(α-methylene−β-butyrolactone) (PMβBL) segment were prepared by salen–aluminum complexes or aminoalkoxybis(phenolate)yttrium amido complex mediated living ring-opening polymerization of racemic α-methylene-β-butyrolactone (rac-MβBL) and different lactones via one-pot, two-step method. These diblock copolymers all consist of semicrystalline and amorphous segments, possessing both a melting point and a glass transition temperature. With the use of simple salenAlMe with bulky (tert-butyldimethylsilyl) groups on the phenolate ortho position as catalyst in conjunction with equivalent benzyl alcohol, MβBL and β-butyrolactone (BL) have nearly identical reactivity in their copolymerization, affording the copolymers P(MβBL-ran-BL) with random distributions of the two monomers. Notably, these copolymers exhibited tunable degradability in the presence of Lewis base, dependent on the MβBL unit content in the random copolymers. Moreover, the vinylidene groups in P(MβBL-r...

Photodegradation characterization and heterogeneity evaluation of the exposed and unexposed faces of stabilized and unstabilized LDPE films

The impact of climatic ageing on the characteristics of both unexposed and exposed faces of unstabilized and stabilized LDPE films was investigated. The effects on chemical and mechanical properties and on the heterogeneity in the films properties were discussed. The exposure periods were 8 and 21months for the unstabilized and stabilized films, respectively. The ATR-FTIR spectra detected initial presence of vinylidene groups that disappeared after 4months of weathering for both faces of the unstabilized films and disappeared earlier for stabilized films. It identifies also a progressive evolution of other photooxidation products, i.e. vinyl and carbonyl groups. The stabilized film demonstrated much better mechanical stability. Considerable reduction in the tensile toughness of unstabilized film was observed. The unstabilized film became quite fragile after 6months of exposure to sunlight to the extent it cannot be tested, while the stabilized film was exposed up to 21months exhibiting much higher durability. The microhardness MH measurements show increasing trend with weathering time and the impact on the exposed face of the unstabilized film was more severe. The ageing resulted in heterogeneity in the films properties and the MH and ATR-FTIR techniques could be used to evaluate its level.

A quantum chemical study of the effect of phosphine ligand on the structure of the Mn and Fe vinylidene binuclear complex

Structures and relative energies of binuclear iron-manganese complexes with the phosphine ligand L, which exist in vinylidene Cp(CO)(L)MnFe(μ-C=CHPh)(CO)4 (2) and benzylidene ketene η4-{C[Mn(CO)(L)Cp]∙ ∙(CO)CHPh}Fe(CO)3 (3) forms are calculated by the B3LYP density functional method. Four isomers with different positions of ligand L relative to the phenyl ring (conformers a and b) and the substituent Ph relative to the С=С bond (conformers E and Z) are considered for each form and their relative stability is determined. It is shown that all isomers of 2 have approximately the same energy (within 4 kcal/mol) whereas the energies of isomers of 3 differ within 21 kcal/mol. Isomer 3Ea in which the PPh3 ligand contacts with the phenyl substituent of the vinylidene group is most energetically favorable. It is found that with an increase in the L ligand size in the order PH3 < PH2Ph < PHPh2 < PPh3 the Mn–P bond length increases to 2.37 A in the most stable isomer of form 3 and to 2.43 A in the isomers of 2 and three conformers of 3. A more substantial increase in the Mn–P bond length in complexes 2 and 3 correlates with their lower stability as compared to isomer Ea of 3, which is consistent with experimental data on the presence of only one conformer 3Ea in solution.

Transformation of carbonyl to vinylidene groups in the π-conjugated peripheral substituent of chlorophyll derivatives by Tebbe reagent

The 131-oxo-moiety of chlorophyll-a derivatives including methyl (pyro)pheophorbides-a, mesopyropheophorbide-a, and bacteriopheophorbide-d possessing vinyl, ethyl, and 1-hydroxyethyl groups, respectively, at the 3-position was transformed into the corresponding exo-methylene group by treatment of Tebbe reagent. The synthetic procedures were useful for the regioselective conversion of the carbonyl to vinylidene group at the 3-position and naturally occurring chlorophyll-d (3-CHO) was successfully modified to chlorophyll-a (3-CHCH2). Under the methylenation conditions, ester–carbonyl, hydroxy, and allyl groups in the peripheral substituents were tolerant as well as an acid-labile magnesium at the central position of chlorophylls.

Simulation Studies of Low-density Polyethylene Production in a Tubular Reactor

This paper deals with the model based of an industrial low-density polyethylene (LDPE) tubular reactor. As the LDPE industry becomes more competitive, manufacturers have to come out with solutions to debottleneck the reactor output while abiding to the stringent product specification. In other words, they have to deal with maximization of the production (maximization of the monomer conversion for a given feed flow rate) and minimization of unwanted product (ethyl, butyl, vinyl and vinylidene groups), while maintaining the polymer product quality with regards to its molecular weight distribution (MWD). To achieve these goals, understanding the effects of operating variables manipulation as well as the dynamic behavior of tubular reactor is essential to develop high performance tubular reactor. In this study, the dynamic model of a tubular reactor for the production of low-density polyethylene (LDPE) is simulated using MATLAB R2015a® in order to predict the temperature profile and monomer conversion percentage along the tubular reactor. The model consists of feed stream, reactor jacket, initiator injector and outlet stream. Several operating variables are involved, notably the feed flow rates, the inlet pressure and temperature with varying parameters to analyze the effect on the reactor productivity. Plots of reactor temperature profile and monomer conversion percentage are presented and from the result, it can be concluded that feed temperature gives significant impact as it effects monomer conversion rate.

Preparation of MMP-sensitive hyaluronic acid hydrogels and their impact on cell migration

Event Abstract Back to Event Preparation of MMP-sensitive hyaluronic acid hydrogels and their impact on cell migration Shan Yu1*, Zhengwei Mao1* and Changyou Gao1* 1 Zhejiang University, Department of Polymer Science and Engineering, China Introduction: Mimicking the structures and functions of extracellular matrix (ECM) is always a important guidance for biomaterials design. ECM takes a key role in signal transduction[1]. For example, enzymes are secreted or locally activited by migrating cells to degrade, and then to remodel the ECM[2]. Therefore, a 3D matrix simulating the structure and function of ECM provides a better model system of physiological environment for cell migration study. Hyaluronic acid (HA) derivatives are widely used in biomedical applications such as drug delivery, wound healing and tissue engineering. The present study mainly focuses on the fabrication of an active and cell-responsive HA-based hydrogel. The migration behaviors of human vascular smooth muscle cells (SMCs) are studied in the 3D matrix. Materials and Methods: HA was modified with methacrylic anhydride under ice bath to introduce the vinylidene groups. The obtained HA derivatives were used as the main structural component of the hydrogel and crosslinked by a peptide through micheal-addition. A peptide sequence (Ac-GCRD-GPQG-IWGQ-DRCG-NH2, MMP-SP) with two –SH groups and sensitive to matrix metalloproteinases (MMPs), a protease family extensively involved in tissue development and remodeling[3], was chosen as cell-responsive crosslinker. The mechanical properties of the hydrogel in water and PBS were characterized, and the degradation behavior in MMP-2 was studied. Figure.1 Schematic illustration of fabrication of HA derivatives, formation of hydrogel, and cell migration of SMCs in 3D matrix. Results and Discussion: Methacrylic anhydride molecules were successfully grafted onto the HA molecules, with a grafting ratio of 50%. The HA hydrogel crosslinked the MMP-sensitive peptide (MMP-SP) showed an obvious degradation tendency in the presence of MMP-2 with a wight loss of nearly 50% in 4 d, while the hydrogel crosslinked by MMP-insensitive dithiothreitol (DTT) showed no obvious weight loss. The hydrogels crosslinked by MMP-SP and DTT showed almost the same mechanical propeties, with a young’s modulus between 2-5 kPa. Cell migration behavior of SMCs in 3D hydrogels will be subsequently studied. Conclusions: Vinylidene-modified HA derivatives were successfully synthesized. Hydrogels that were sensitive to MMPs were fabricated for subsequent cell migration study. Natural Science Foundation of China (21434006 and 21374097)

α‐exomethylene lactone possessing acetal–ester linkage: Polymerization and postpolymerization modification for water‐soluble polymer

ABSTRACT2,6‐Dimethyl‐5‐methylene‐1,3‐dioxa‐4‐one (DMDO), a cyclic acrylate possessing acetal–ester linkage, was obtained as a mixture of cis‐ and trans‐isomers (95:5) from Baylis–Hillman reaction of an aryl acrylate. The radical and anionic polymerizations of DMDO yielded the corresponding vinyl polymers without any side reactions such as cleavage of the acetal–ester linkage. The polymerization behaviors were significantly different from that of the acyclic acrylate, α‐(hydroxymethyl)acrylic acid, which was expected inactive against polymerization due to the steric hindrance around the vinylidene group by the α‐substituent. The acetal–ester linkage of the obtained polymer (P1) was completely cleaved via acid hydrolysis to afford a water soluble polymer, P2. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 955–961

Regio‐chemistry control in propylene/isoprene copolymerization by metallocene catalysts

AbstractRegio‐chemistry control in copolymerization of propylene with isoprene is pursued with C2‐symmetric ansa‐metallocene catalysts in order to efficiently synthesize isotactic polypropylene bearing pendant vinylidene functionality (iPP‐g‐VD) using isoprene as a convenient asymmetric diene feedstock. Two paths are taken by employing two well‐known but structurally different metallocenes that exhibit discrepant regio‐chemistry for α‐olefin insertion, namely rac‐Me2Si(2‐Me‐4‐Ph‐Ind)2ZrCl2 (1) and rac‐CH2(3‐t‐Bu‐Ind)2ZrCl2 (2), both of which tend to an improvement of isoprene 4,3‐ (primary) insertion specificity whilst depressing the regio‐reversed 3,4‐ (secondary) insertion. In the case of using 1–methylaluminoxane (MAO), the strategy is to use increased dosage of H2 to effectively integrate isoprene 3,4‐insertion into iPP main chain without developing π‐allyl–metal deadlock. In the case of using 2–MAO, however, the sterically highly hindered ligand structure only accommodates primary isoprene 4,3‐insertion. Synthesis of iPP‐g‐VD becomes much more controllable, with up to 1.91 mol% of side‐chain vinylidene groups having been realized on iPP, at fairly good catalyst activities and little or no sacrifice of polymer molecular weight. iPP‐g‐VD is revealed to be fully eligible as an intermediate for accessing polar‐functionalized polypropylene, with both hydroboration and subsequent hydroxylated functionalization and poly(methyl methacrylate) grafting proceeding with high yields. © 2015 Society of Chemical Industry

Self-beating artificial cells: design of cross-linked polymersomes showing self-oscillating motion.

Biomimetic cross-linked polymersomes that exhibit a self-beating motion without any on-off switching are developed. The polymersomes are made from a well-defined synthetic thermoresponsive diblock copolymer, and the thermoresponsive segment includes ruthenium catalysts for the oscillatory chemical reaction and vinylidene groups to cross-link the polymersomes. Autonomous volume and shape oscillations of the cross-linked polymersomes are realized following redox changes of the catalysts.

Characterization of typical infrared characteristic peaks of hydrogen in nitrogen and hydrogen co-doped diamond crystals

The 3107 cm-1 peak is observed in the infrared absorption spectra of all types of Ia diamonds, but it has not been observed in the iron-based catalyst. A series of nitrogen and hydrogen-doped diamond crystals is successfully synthesized using P3N5 as the nitrogen source in a catalyst-carbon system at a lower pressure and temperature (6.3 GPa, 1500 ℃). Fourier transform infrared micro-spectroscopy reveals that the hydrogen atoms existing in the synthesized diamond are in two forms. The one is attributed to the CH bond stretching (3107 cm-1) and bending (1405 cm-1) vibrations of the vinylidene group (C＝CH2). The other is due to sp3 hybridization CH bond symmetric (2850 cm-1) and anti-symmetric (2920 cm-1) vibrations. According to our result, we find that the 3107 cm-1 hydrogen absorption peak is related to the aggregated nitrogen in synthetic diamond. The 3107 cm-1 peak could not be observed in synthetic diamond without aggregated nitrogen, even if it has a high nitrogen concentration. And the hydrogen absorption peaks at 2920 and 2850 cm-1 are more widespread than the absorption peak at 3107 cm-1, this suggests that the sp3 CH bond more widely exists in diamond than the vinylidene group (C＝CH2). Infrared spectra analysis indicates that the hydrogen impurity mainly exists in the natural diamond as vinylidene group as seen from the absorption peak intensity. We believe that our results provide a new way to study the formation mechanism of the natural diamond. Moreover, the ideal synthesis condition in our system supplies a possible way for us to design n-type diamond semiconductor.

New guests for the cucurbit[8]uril host. Formation of G2H ternary complexes

On the basis of the highly stable G2H (2 : 1) ternary complex formed by two methyl viologen cation radicals inside the cavity of cucurbit[8]uril, we prepared three monocationic 4‐phenylpyridinium derivatives: 1‐(hydroxyethyl)‐4‐phenyl‐pyridinium (1+) bromide, 1‐(octaethyleneglycol)‐4‐phenyl‐pyridinium (2+) chloride, and 4‐[4‐(methoxymethoxy)phenyl]pyridinium (3+) iodide, as possible guests for 2 : 1 complexation inside cucurbit[8]uril. We also investigated a fourth monocationic guest (4+), in which a central vinylidene group is inserted to elongate the 4‐phenyl‐pyridinium residue. Using 1H NMR and UV–Vis spectroscopic data and mass spectrometric data, we obtained unequivocal evidence for the formation of G2H (2 : 1) ternary complexes in all cases. The stoichiometry of the complexes was further verified by continuous variation (Job) plots, and in some cases, high resolution ESI‐MS spectrometric data. Diffusion coefficient measurements, using 1H NMR pulse gradient spin echo techniques, yielded values consistent with the formation and expected structures of the ternary complexes. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Effect of extrusion screw speed on biocomposite thermo-mechanical properties

Thermo-mechanical, optical and physical properties of polypropylene (PP)/lignocellulosic fibre-filled/maleated PP composites were studied as a function of extrusion screw speeds. All materials were extruded at four screw speeds and injection moulded as dogbone specimens. The density, yellowness index (YI) and Fourier-transform infrared spectra were determined for the processed specimens. Tensile properties and coefficient of linear thermal expansion (CLTE) were also determined. The densities of the composites remained constant within the same composition. YI and absorbances of carbonyl, vinylidene and hydroxyl groups, which are indicators of thermo-oxidation, decreased with a shorter extruder residence time. The CLTE and tensile properties showed peak properties at intermediate screw speeds. The analysis suggested optimising the residence time assisting in achieving a balance of properties.

Formation of Vinylidene in Polypropylene/Ethylene Vinyl Acetate (PP/EVA) Blends During Degradation

The effect of natural exposure and artificial weathering on selected properties of PP/EVA blends was investigated. The vinyl acetate concentration decreased with exposure time due to acetylation. The most pronounced effect of radiation is associated with oxidative degradation. The cross-linking of PP/EVA blends was attributed to the formation of vinylidene group. Weathering decreased the tensile strength, elongation at break, and Young's modulus of the naturally and artificially exposed blends. This reduction was the result of blends’ molecular weight reduction due to the degradation induced by weathering.

Oxidation and crosslinking processes during thermal aging of low‐density polyethylene films

AbstractThis work analyzes the influence of thermal degradation on the microstructure and the mechanical properties of low‐density polyethylene subjected to aging at 70°C in the dark for times up to 21 months. It is found that the polymer shows a gradual increase of its elastic modulus and a dramatic reduction of its ductility, due to secondary crystallization. Infrared spectroscopy (FTIR) reveals the autoaccelerated oxidation of the polymer after 5 months aging. It is observed that the unsaturated vinylidene groups initially present in the material are gradually overridden by vinyl groups and, eventually, by t‐vinylene groups. Nuclear magnetic resonance (13C NMR) shows that the initial butyl chain branches are progressively completed by shorter ramifications, namely ethyl branches. These results are discussed in term of macromolecular mechanisms: (i) oxidation, (ii) chain scission, and (iii) crosslinking. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011