Isoprene Research Articles (Page 1)

Thiol-functionalized ESIPT dye in rubber matrices: Mechanically robust, fluorescent, and reversible solid-state pH sensors.

Ground-level ozone (O3) pollution is a problem when managing air quality in China, and biogenic volatile organic compounds (BVOCs) are key precursors of O3 formation. Vegetation type and temperature influence BVOC emissions, yet the differences in emissions across vegetation types and their temperature responses still exhibit significant uncertainties. This study was focused on the Sichuan Basin in China. It used the G95 model to develop a high-resolution BVOC emission inventory, allowing the analysis of emission characteristics for different vegetation types. The study also used a temperature sensitivity algorithm to assess how temperature changes affect BVOC emissions. The impact of these emissions on regional O3 formation potential (OFP) was then quantified using the OFP method. The results show significant differences in BVOC emissions across vegetation types. Forests at the basin edges (mixed, broad-leaved, and coniferous) have much higher emission intensity (10.5 t/km2) than agricultural areas in the center of the basin (0.15 t/km2). In terms of composition, monoterpenes (MON) mainly dominate mixed and coniferous forests (42.28% and 58.37%, respectively), while isoprene (ISOP) dominates broad-leaved forests (64.02%). The study found that temperature generally increases BVOC emissions, which vary by vegetation type. Broad-leaved forests have the highest temperature sensitivity (3.94%), much higher than agricultural vegetation (0.03%). BVOC emissions exhibit a seasonal pattern of “high in summer, low in winter” and a spatial pattern of “high at the edges, low at the center”. Temperature also influences emission intensity and composition, thus driving variations in the potential for O3 formation. Seasonally, different vegetation types show structural changes in OFP contribution. Broad-leaved forests, dominated by ISOP, show a significant increase in summer contribution (+8.0%), becoming the main source of O3 precursors. In contrast, mixed forests, dominated by MON, show a clear decrease in summer contribution (−6.3%).

Polybutadiene (PB) and polyisoprene (PI) rubbers are indispensable synthetic elastomeric materials widely used in tires, footwear, hose, belts, sealants, electricity, construction, and other applications. Nowadays, PB and PI elastomers are produced from butadiene (BD) and isoprene (IP) monomers via transition-metal-mediated coordination polymerization. Transition metal catalytic systems consist of a precise characteristic structural unit at the molecular level: well known as “single-site catalysts” (SSCs). These have experienced a revolutionary advance in the recently developed conjugated dienes synthetic rubber method. Among the SSCs, a class of rare-earth, metal-centered half-sandwich molecule has been identified as a high-performance catalytic system for conjugated dienes polymerization. These novel half-sandwich rare-earth (HSRE) catalytic systems exhibit several irreplaceable advantages compared with the conventional Ziegler–Natta-type catalytic systems. These HSRE catalytic systems can create novel conjugated diene rubbers (CDRs) with high catalytic reactivity, high stereoselectivity, an adjustable polymer chain microstructure, and high molecular weights and are considered to be the next generation of ecofriendly and economic catalytic systems for industrial applications. This paper delivers a concise review of some important synthetic methods for representative HSRE complexes with characteristic structures and of the utilization of some HSRE catalytic systems for the preparation of high-performance CDRs, especially highly stereoregular PI and PB materials.

Abstract. The use of urban green spaces (UGSs), such as parks and gardens, is widely promoted as a strategy to improve the urban atmospheric environment. However, this study reveals that it can exacerbate urban ozone (O3) levels under certain conditions, as demonstrated by a September 2017 study in Guangzhou, China. Using the Weather Research and Forecasting model with the Model of Emissions of Gases and Aerosols from Nature (WRF-MEGAN) and the Community Multiscale Air Quality (CMAQ) model, we assessed the impact of UGS-related biogenic volatile organic compound (BVOC) emissions (hereafter referred to as UGS-BVOC emissions) on urban O3. Our findings indicate that the UGS-BVOC emissions in Guangzhou amounted to 666 Gg (∼90Mgkm-2), with isoprene (ISOP) and monoterpene (TERP) contributing remarkably to the total UGS-BVOC emissions. Compared to anthropogenic VOC (AVOC) and BVOC emissions, UGS-BVOC emissions account for ∼33.45 % in the city center, and their inclusion in the model reduces ISOP underestimation. The study shows improved simulation mean biases for MDA8 (maximum daily 8 h average) O3, from −3.63 to −0.75 ppb in the city center. Integrating UGS-BVOC emissions and UGS-LUCC emissions (where LUCC denotes land use cover change) enhances surface monthly mean O3 by 1.7–3.7 ppb (+3.8%-8.5%) and adds up to 8.9 ppb (+10.0 %) to MDA8 O3 during pollution episodes. UGS-BVOC emissions alone increase monthly mean O3 by 1.0–1.4 ppb (+2.3%-3.2%) in urban areas and contribute up to 2.9 ppb (+3.3 %) to MDA8 O3 during pollution episodes. These impacts can extend to surrounding suburban and rural areas through regional transport, highlighting the need to accurately account for UGS-BVOC emissions to better manage air quality.

Bis-(o-dipheylphosphinophenyl)amine, a tridentate (PNP) chelating ligand, and several of their Rare Earth (RE) metal complexes, [bis-(o-dipheylphosphinophenyl)amido]-RER2, {[(C6H5)2P-o-(C6H4)]2NMR2 (R = -CH2-o-(C6H4)NMe2: M = Y, 1; Nd, 2; Gd, 3;), are prepared in high yields. When activated with the strong Lewis acid MMAO-7, all these complexes exhibit catalytic activity toward the polymerization of isoprene (IP) in non-protic hydrocarbons. While the Nd complex (2) showed moderate activity and stereoselectivity, the Y and Gd complexes (1 and 3) exhibited extremely high catalytic efficiency in IP homo-polymerization, and produced polyisoprene rubber (PI) with 95% to over 99% cis-1,4 stereoselectivity and narrow polydispersity indices (<2.0). Moreover, under industrially relevant conditions, complex 3 can catalyze IP to produce ultrahigh molecular weight PI (UHMW-PI, MW up to 1200-2600 kg/mol) rubber with a very narrow polydispersity index (PDI ca. 1.1-1.6), a high-performance elastomeric material mimic of natural rubber (NR).

Insect herbivory can influence tree growth, community structure and ecological processes in forest ecosystems. We investigated the effects of insect herbivory and leaf defoliation on the emission of biogenic volatile organic compounds (BVOCs), isoprene (ISO) and monoterpenes (MTs) in Cinnamomum camphora (broad-leaf tree) and Cryptomeria japonica (coniferous tree), and explored the underlying mechanisms by measuring leaf phy-siological characteristics such as photosynthetic parameters and chlorophyll fluorescence. The results showed that insect herbivory and leaf defoliation increased the emission of BVOCs from the leaves of both species compared to the control. Three days after the completion of insect herbivory treatment, the emission flux of ISO in C. camphora and C. japonica increased by 4.9 and 3.1 times, respectively, while leaf defoliation increased the ISO emission flux of C. camphora by 4.6 times. Insect herbivory increased photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate in C. camphora, but did not affect the photosynthetic parameters of C. japonica. In contrast, leaf defoliation significantly reduced chlorophyll fluorescence parameters in C. japonica. The Pearson correlation analysis and structural equation modeling showed that the emission of ISO and MTs from C. camphora leaves significantly correlated with photosynthetic and chlorophyll fluorescence parameters. Compared to chlorophyll fluorescence parameters, photosynthetic parameters had a greater influence on the emission of ISO and MTs. For C. japonica, ISO emission was significantly correlated with chlorophyll fluorescence parameters, and chemical induction due to insect herbivory having a more pronounced effect on ISO emission. In conclusion, our results indicated that insect herbivory could enhance the emission of BVOCs, but the response mechanism varied with tree species. For C. camphora, the increase in BVOC emission was due to the enhanced photosynthetic rates. The chemical induction resulting from insect herbivory played a more important role in increasing BVOC release from C. japonica.

Cis-1,4-specific polymerization of 1,3-conjugated dienes with bis(benzimidazole)NiCl2 catalyst system

The influence of myrcene on anionic copolymerization of 1,3-pentadiene and styrene

Capability of isoprene and butadiene as comonomers under metallocene catalysis: Activating active sites with the addition of 1-hexene and propylene

We have developed a versatile scalable triblock polymer system for anion exchange membrane (AEM) based electrochemical energy conversion devices. This system is uniquely suited to solving both the membrane and ionomer challenges for the commercialization of AEM water electrolysis or fuel cells. Using our advanced fundamental understanding of AEMs based on our work which began in 2010, we can design systems from first principles to match the needs of the device. A triblock ABA polymer is readily fabricated that has both chemical and mechanical stability. The synthesis of these systems is robust, high yield and amenable to high volume production. It utilizes a novel dual chain transfer agent to mediate the chain-transfer ring-opening metathesis polymerization (ROMP) of cyclooctene (COE) or the polymerization of isoprene (IP) to give the hydrophobic B block of the polymer. This is followed by the reversible addition-fragmentation chain transfer radial polymerization of chloromethylstyrene (CMS). The polyCMS (pCMS) blocks are then quaternized with an amine to give the cationic hydrophilic A block. Before quaternization the B block is hydrogenated to give either semi-crystalline polyethylene (pE) or amorphous polymethylbutylene (pMB) from pCOE and pIP respectively. The obvious achilles heal in this system from a chemical durability standpoint is the linking ether functionality between the hydrophobic and hydrophilic blocks. The material we have synthesized to date have exceptional chemical and mechanical stability. It performs very well in ex-situ testing with KOH solutions and in device testing we have demonstrated >500 h at 50°C in water electrolysis in 5 cm2 cells in 1M carbonate electrolyte at 0.5 A cm-2. We attribute the chemical stability to the fact that we post quaternize the membrane to give methylpipiridinium cations and we assume that this reaction does not fully penetrate down the hydrophilic chain. This leaves a hydrophobic un-quaternized region close to the hydrophobic block that does not allow access to the ether linkage by the hydrated hydroxide anion. Recently a new approach to the telehelic mid block pCOE has been reported that has no ether linkages and allows the hydrophobic outer blocks to be linked by a methylene linker. This gives use an opportunity to directly contrast the chemical stability of two identical triblock co-polymers one with an ether linkage and one with a methylene linkage between blocks. In this presentation we will show the results from ex-situ chemical stability test one at low temperatures and higher hydroxide concentration and one at higher temperature and lower hydroxide concentration. There are many examples in polymer electrolyte chemistry where a simple change leads to unintended consequences. The geometry of the ether linkage versus the methylene linkage will change the way that the polymer chains will organize and entangle in ways that are not currently predictable. To probe the mechanical, chemical and morphological difference between these two polymers we will fully characterize and contrast both polymers physical chemical properties including water uptake, ionic conductivity, DSC, TGA, tensile strength and morphology through SAXS, WAXS and HRTEM. Data for the two polymer membranes will also be contrasted and compared in small laboratory 5 cm2 single cells for both electrolysis in dilute carbonate and H2/O2 fuel cells using conventional catalysts.

Abstract Reversible cross‐linked structures are widely used to turn thermoset plastics into recyclable and self‐healing vitrimer materials, but seldom applied in traditional flexible rubber/ceramic composites. In this paper, dioxaborolanes based flexible poly (isoprene (IP)‐co‐acrylonitrile (AN)) vitrimer is synthesized as the rubber matrix by copolymerizing with functional monomers at 5°C for 7 h, and mixed with 5 wt% modified barium titanates (BT) to prepare flexible high dielectric vitrimer composite. The materials are characterized by FTIR, TGA, SEM, DMA, etc. The results indicate that reversible crosslinking can occur above 76.4°C, and copolymerizing with the dioxaborolanes based monomers can turn poly (IP‐co‐AN) into the flexible vitrimer. The poly (IP‐co‐AN)/BT vitrimer composite not only shows a good thermal stability below 145.6°C, but also exhibits an excellent particle dispersivity and a certain self‐healing function at 80°C. The poly (IP‐co‐AN)/BT vitrimer composite has a storage modulus E' about 3.18 MPa at 25°C and T g about −5.4°C, and shows a higher relative permittivity about 7.5 and lower dielectric loss about 0.156 at 1 k Hz. The results indicate that this paper provides a new method to achieve multifunction and high dielectricity for composites. Highlight Reversible cross‐linked structures are applied in rubber / ceramic composites Cross‐linked flexible composites are reprocessable and self‐healing Reversible bonds between particles and matrix improve compatibility Synergism of BaTiO 3 and cross‐linked structure enhances dielectric properties

To overcome the unconventional polymerization behavior of single-site symmetrical metallocene catalyst in the presence of borate

A series of well-defined diblock copolymers, namely, 3,4-polyisoprene-block-syndiotactic-1,2-polybutadiene (3,4-PI-b-s-1,2-PBD), with a soft-hard block sequence were synthesized via an in situ sequential polymerization process using a robust iron-based catalytic system Fe(acac)3/(isocyanoimino) triptenylphosphorane (IITP)/AliBu3. This catalyst exhibits vigorous activity and temperature tolerance, achieving a polymerization activity of 5.41 × 106 g mol(Fe)-1 h-1 at 70 °C with a [IP]/[Fe] ratio of 15,000. Moreover, the quasi-living polymerization characteristics of the catalyst were verified through kinetic experiments. The first-stage polymerization of isoprene (IP) is performed at 30 °C to give a soft 3,4-PI block, and then a quantitative amount of 1,3-butadiene was added in situ to the quasi-living polymerization system to produce a second hard s-1,2-PBD. The s-1,2-PBD segments in block copolymers display a rodlike morphology contrasting with the spherulitic morphology characteristic of s-1,2-PBD homopolymers. The precise tunability of the length of the soft and hard chain segments of these novel elastic materials with the feed ratio of IP and BD, endowing them with outstanding mechanical properties and excellent dynamic mechanical properties, which are expected to be promising high-performance rubber materials.

The results of research on epoxidation technology from concentrated natural rubber latex (CNRL) and in-situ peroxyformic acid, which is synthesised from formic acid (FA) and hydrogen peroxide (HP), are presented in the article. The study investigated the influence of technological parameters of the epoxidation process, such as stabiliser content (nonylphenol ethoxylate, NP9), dry rubber content (DRC), isoprene, stirring speed, reaction time, reaction temperature, and molar ratios of hydrogen peroxide and isoprene (IP), on the epoxy resin content of the product. Research results have shown that the epoxidation reaction with NP9 at 10% takes from 2.5 to 20 hours under the following conditions: latex composition contains from 16 to 24% DRC, stirring speed 100 rpm, reaction temperature response 30 to 70 °C, HP/IP molar ratio changes from 0.7 to 1.3, FA/IP ratio is 0.2, the product was stable and without coagulation. The product was obtained with an epoxy content of 23.4 to 43.6%. This is the basis for building an epoxidized natural rubber (ENR) production process to create a series of natural rubber products that are renewable, environmentally friendly, low-cost, and have many industrial applications.

Herein, a concise, effective, and scalable strategy is reported that the introduction of polar molecules (PMs) (e.g., anisole (PhOMe), phenetole (PhOEt), 2-methoxynaphthalene (NaphOMe), thioanisole (PhSMe), and N,N-dimethylaniline (PhNMe2)) as continuously coordinated neutral ligand of cationic active species in situ generated from the constrain-geometry-configuration-type rare-earth metal complexes A-F/AliBu3/[Ph3C][B(C6F5)4] ternary systems can easily switch the regio- and stereoselectivity of the polymerization of conjugated dienes (CDs, including 2-subsituted CDs such as isoprene (IP) and myrcene (MY), 1,2-disubstituted CD ocimene (OC), and 1-substituted polar CD 1-(para-methoxyphenyl)-1,3-butadiene (p-MOPB)) from poor selectivities to high selectivities (for IP and MY: 3,4-selectivity up to 99%; for OC: trans-1,2-selectivity up to 93% (mm up to 90%); for p-MOPB: 3,4-syndioselectivity (3,4- up to 99%, rrrr up to 96%)). DFT calculations explain the continuous coordination roles of PMs on the regulation of the regio- and stereoselectivity of the polymerization of CDs. In comparison with the traditional strategies, this strategy by adding some common PMs is easier and more convenient, decreasing the synthetic cost and complex operation of new metal catalyst and cocatalyst. Such regio- and stereoselective regulation method by using PMs is not reported for the coordination polymerization of olefins catalyzed by rare-earth metal and early transition metal complexes.

Investigating the sensing efficiency of C6O6Li6 for detecting lung cancer-related volatile organic compounds: A computational density functional theory approach

Transient interaction effects of temperature and light intensity on isoprene and monoterpene emissions from Schima superba and Phoebe bournei

Ethylene (E) copolymers with isoprene (IP) possessing higher glass-transition temperatures (Tg values, −7.1 to 29.2 °C) than those prepared by the reported catalysts (Tg below −18 °C) have been prepared in the copolymerization by using half-titanocene catalysts containing phenoxide ligand, Cp′TiCl2(O-2,6-iPr2-4-R-C6H2) [Cp′ = C5Me5 (Cp*), R = H (1), SiEt3 (2)]. Their microstructural analysis by NMR spectra revealed that the copolymers contained cyclopentane (major) and cyclohexane units, formed by cyclization after IP and subsequent ethylene insertions, in addition to 1,4- and 3,4-IP inserted units observed as major units in those prepared by reported catalysts. The 1,2,4-Me3C5H2 analogue (R = H) showed better IP incorporation, but the resulting E/IP copolymers possessed rather low Tg values compared to those prepared by 1,2 due to less cyclopentane unit in the microstructure. The Tg value in the E/IP copolymer increased upon the increase of the IP content, and the degree was dependent upon the catalyst employed. Due to their unique microstructure, the resulting E/IP copolymers prepared by 1,2–MAO catalyst systems exhibit promising tensile and elastic properties. The tensile strength initially decreased with an increase in the IP content along with an increase of the elongation at break (up to 600%, IP 3.3–15.6 mol %) and then increased gradually with further increase in the IP contents (IP 18.1–21.5 mol %); the elongation at break then decreased with preserving the tensile strength along with the observation of the yield stress.

Ozone (O3) pollution affects plant growth and isoprene (ISO) emission. However, the response mechanism of isoprene emission rate (ISOrate) to elevated O3 (EO3) remains poorly understood. ISOrate was investigated in two genotypes (diploid and triploid) of Chinese white poplar (Populus tomentosa Carr.) exposed to EO3 in an open top chamber system. The triploid genotype had higher photosynthetic rate (A) and stomatal conductance (gs) than the diploid one. EO3 significantly decreased A, gs, and ISOrate of middle and lower leaves in both genotypes. In the diploid genotype, the reduction of ISOrate was caused by a systematic decrease related to ISO synthesis capacity, as indicated by decreased contents of the isoprene precursor dimethylallyl diphosphate and decreased isoprene synthase protein and activity. On the other hand, the negative effect of O3 on ISOrate of the triploid genotype did not result from inhibited ISO synthesis capacity, but from increased ISO oxidative loss within the leaf. Our findings will be useful for breeding poplar genotypes with high yield and lower ISOrate, depending on local atmospheric volatile organic compound/NOx ratio, to cope with both the rising O3 concentrations and increasing biomass demand. They can also inform the incorporation of O3 effects into process-based models of isoprene emission.

Whole-plant compensatory responses of isoprene emission from hybrid poplar seedlings exposed to elevated ozone