Polymerization Of Dienes Research Articles

In Situ Efficient End Functionalization of Polyisoprene by Epoxide Compounds via Neodymium-Mediated Coordinative Chain Transfer Polymerization.

The Nd-mediated coordinative chain transfer polymerization (CCTP) of dienes represents one of the state-of-the-art techniques in the current synthetic rubber field. Besides having well-controlled polymerization behaviors as well as high atom economies, it also allows for the generation of highly reactive Al-capped polydienyl chain-ends, which hold great potential, yet much less explored up to date, in achieving end functionalization to mimic the structure of natural rubber. In this study, we demonstrate an efficient in situ method to realize end-functionalizing polyisoprene by introducing epoxide compounds into a CCTP system. The end functionalization efficiency was 92.7%, and the obtained polymers were systematically characterized by 1H NMR, 1H,1H-COSY NMR, DOSY NMR, and MALDI TOF. NMR studies revealed that a maximum of two EO units were introduced to the chain ends, and based on density functional theory (DFT) studies, an energy barrier of 33.3 kcal/mol was required to be overcome to open the ring of the EO monomer. Increasing the ratio of [Ip]/[Nd] resulted in gradually increased viscosities for the reaction medium and therefore gave rise to an end functionalization efficiency that decreased from 92.7% to 74.2%. The end hydroxyl group can also be readily converted to other functionalities, as confirmed by NMR spectroscopy.

Exploring Catalytic Intermediates in Pd-Catalyzed Aerobic Oxidative Amination of 1,3-Dienes: Multiple Metal Interactions of the Palladium Nanoclusters.

Metal nanoclusters (NCs) have unique properties because of their small size, which makes them useful as catalysts in reactions like cross-coupling. Pd-catalyzed oxidative amination, which involves dehydrogenative C-N bond formation, uses Pd complexes as the active species. It is known that the catalytic conditions involve the formation of Pd(0) species from Pd NCs, but the precise role of Pd NCs in the transformations has not been established. In this study, we investigated the characteristic properties of Pd NCs in oxidative amination of 1,3-dienes. The reaction achieved direct amination of commercially accessible 1,3-dienes with secondary aromatic amines, providing a variety of nitrogen containing 1,3-dienes. The compound was applicable to radical polymerization to provide the nitrogen-fabricated 1,3-diene-based polymer, which exhibited a different thermal stability compared to aliphatic nitrogen-fabricated diene polymers. In addition to the synthetic utility, by combining X-ray absorption fine structure and small-angle X-ray scattering analysis, we revealed amines and 1,3-dienes affected metal leaching from the Pd nanoparticles and stabilization of Pd NCs in the catalytic reaction. Additionally, DFT calculation suggested that the catalytic intermediate contained multiple adjacent Pd atoms and was responsible for formation of an σ-allylic intermediate that is difficult to form with the use of Pd complexes. These results could be used to understand the underlying phenomenon in the oxidative coupling reaction and develop Pd NCs-based dehydrogenation.

Synthesis of Cycloaliphatic Polyamides via Palladium-Catalyzed Hydroaminocarbonylative Polymerization.

Polyamides represent one class of materials that is important in modern society. Because of the numerous potential applications of polyamides in various fields, there is a high demand for new polyamide structures, which necessitates the development of new polymerization methods. Herein, we report a novel and efficient palladium-catalyzed hydroaminocarbonylative polymerization of dienes and diamines for the synthesis of cycloaliphatic polyamides. The method employs readily available starting materials, proceeds in an atom-economic manner, and creates a series of new functional polyamides in high yields and high molecular weights. In contrast with the traditional polyamides based on adipic acid, the cycloaliphatic polyamides have superior thermal resistance, higher glass-transition temperature, and better solubility in common organic solvents, thus probably featuring the merits of high-performance and good processability.

Green perspective drives the renaissance of anionic diene polymerization

Polymers based on 1,3-diene monomers play a pivotal role in many commercial elastomers and thermoplastic elastomers. This review summarizes the state of the art and recent developments in the living anionic polymerization of dienes.

Neodymium-Mediated Coordinative Chain Transfer Polymerization of Isoprene in the Presence of External Donors.

Nd-based polydiene elastomers, including NdIR and NdBR, are regarded as indispensable key raw materials in preparing green tires with excellent performance capabilities, but their wide application is still limited by the relative higher cost of Nd precatalysts. Nd-mediated coordinative chain transfer polymerization (CCTP) of diene provides an effective strategy to reduce the precatalyst cost, because this method involves very high atom economy, i.e., each Nd molecule can generate multiple polymer chains. Nevertheless, all possible factors that could influence such CCTP behaviors are still mostly unexplored to date. In this report, the basic chemistry on the influence of external donors on the overall CCTP behaviors of isoprene was established for the first time. It was found that increasing the amount of external donors had a negative influence on the chain transfer efficiencies, resulting in gradually decreasing atom economies. Catalyst addition order studies revealed that the coordination of donors with cationic Nd active species, rather than alkylaluminium CTAs, contributed mostly to such decreased efficiencies. Moreover, it was found that when the ratio of donors and Nd compounds was higher than 1.0, the CCTP behaviors were corrupted, resulting in polymers with broad distributions, as well as resulting in low atom economies; nevertheless, when the ratio was lower than 0.5, the system still displayed CCTP characteristics, implying that the critical ratio for maintaining the CCTP was 0.5. Additionally, when such a ratio was 0.01, the high atom economy was almost the same as donor-free CCTP systems. Detailed kinetic studies at such a ratio demonstrated that the donor-contained system proceeded in a well-controlled manner, as concluded from the good linear relationship between the Mn of the PIps against the polymer yields, as well as the good linearity between the Mn against the (IP)/(Nd) ratios. Such maintained CCTP properties also allowed for seeding two-step polymerizations to prepare diblock copolymers with precisely controlled molecular weights. Expanding the types of donors to more phosphine, oxygen, and nitrogen containing compounds showed that they also affected the CCTP behaviors depending on their steric and electronic properties.

Ansa-metallocene catalyst based on 3-phenyl and 4-methyl substituted: catalyst evaluation in conjugated and non-conjugated diene polymerization

Ansa-metallocene catalyst based on 3-phenyl and 4-methyl substituted: catalyst evaluation in conjugated and non-conjugated diene polymerization

Transition Metal-(μ-Cl)-Aluminum Bonding in α-Olefin and Diene Chemistry.

Olefin and diene transformations, catalyzed by organoaluminum-activated metal complexes, are widely used in synthetic organic chemistry and form the basis of major petrochemical processes. However, the role of M-(μ-Cl)-Al bonding, being proven for certain >C=C< functionalization reactions, remains unclear and debated for essentially more important industrial processes such as oligomerization and polymerization of α-olefins and conjugated dienes. Numerous publications indirectly point at the significance of M-(μ-Cl)-Al bonding in Ziegler-Natta and related transformations, but only a few studies contain experimental or at least theoretical evidence of the involvement of M-(μ-Cl)-Al species into catalytic cycles. In the present review, we have compiled data on the formation of M-(μ-Cl)-Al complexes (M = Ti, Zr, V, Cr, Ni), their molecular structure, and reactivity towards olefins and dienes. The possible role of similar complexes in the functionalization, oligomerization and polymerization of α-olefins and dienes is discussed in the present review through the prism of the further development of Ziegler-Natta processes and beyond.

Fe‐based catalyst with diphenylphosphite as donor for stereopolymerization of butadiene, isoprene, and myrcene

AbstractIron catalyst has been encountered with low activity and stereoselectivity sensitive to the operational conditions for diene polymerization. In this study, diphenylphosphite has been proved as an efficient donor in iron‐based tertiary catalyst for butadiene, isoprene and myrcene stereopolymerizations. Thermal robustness of active species has been demonstrated as the high activity and 1,2 stereoselectivity are survived in a wide temperature scope ranging from 5°C to 80°C. The resultant polybutadienes are found to have 1,2 incorporation up to 92.8% with syndiotactic conformation (rrrr: 95.1%), and more than 65% of irregular 3,4 enchainments are generated for polyisoprene and polymyrcene. The active species are formed preferably following addition sequence of iron compound, donor and activator in the presence of monomer. The development of this highly active and stable catalyst combining cost‐efficient components and mild operation parameters could provide accessible catalyst recipe to produce new types of polydienes.

Making Polyisoprene Self‐Healable through Microstructure Regulation by Rare‐Earth Catalysts

AbstractThe creation of self‐healing polymers from commodity olefins is of great interest and importance but has remained a challenge to date. We report here for the first time the synthesis of self‐healing polymers by catalyst‐controlled polymerization of a simple commodity diene, isoprene. We found that polyisoprenes having an appropriate mixture (ca. 70/30) of 3,4‐ and cis‐1,4‐microstructures synthesized by using a half‐sandwich scandium catalyst could act as excellent self‐healing elastomers without any external intervention. The unprecedented self‐healability could be ascribed to nanoscale heterogeneities formed by microphase separation of the relatively hard 3,4‐segments from a flexible cis‐1,4‐segment matrix. The hydrogenated polyisoprenes (without C=C bonds) with the analogous microstructures also exhibited excellent mechanical and self‐healing properties, further demonstrating that even simple polyolefins can be made self‐healable if the microstructures are appropriately regulated.

Outdoor playgrounds and climate change: Importance of surface materials and shade to extend play time and prevent burn injuries

Surfaces in outdoor playgrounds get hot in the sun and can cause serious skin burns in children. In-situ measurements from 10 playgrounds in Sydney showed that the maximum and average surface temperatures of sun-exposed playground equipment and flooring surfaces were frequently above skin contact burn thresholds. Black and dark-coloured wet pour rubber and synthetic turf were the hottest floor materials, all having maximum surface temperatures (Ts_max) > 80 °C. A blue rubber dolphin was the hottest piece of play equipment, with a Ts_max of 91.8 °C. A systematic assessment of common synthetic flooring materials exposed to full sun showed notable differences in Ts_max between material types and colour-tones. Synthetic turf with 40 mm long grass blades (STlng-GR) was the hottest material (Ts_max = 84.5 °C), followed by dark blue styrene butadiene rubber (SBRD-BL, Ts_max = 81.1 °C), dark green ethylene propylene diene polymer (EPDMD-GR-2, Ts_max = 77.8 °C), dark brown thermoplastic vulcanizate (TPVD-BR, Ts_max = 71.8 °C), and intermediate blue thermoplastic polyolefin (TPOI-BL, Ts_max = 65.0 °C). All these materials were hot enough to cause contact burns on typical, warm summer days when children are likely to visit outdoor playgrounds. Surface temperatures were significantly reduced in the shade and never reached burn threshold temperatures. Selection of appropriate material type and colour-tone, together with the provision of shade can remove the hazard risk for contact skin burns from outdoor playgrounds. Results of this work will assist playground designers and managers to provide safer places for our children to play longer in increasingly warmer summers.

Progress toward Polymerization Reaction Monitoring with Different Dienes: How Small Amounts of Dienes Affect ansa-Zirconocenes/Borate/Triisobutylaluminium Catalyst Systems.

The objectives of this work were to address the fundamental characteristics of ansa-zirconocene catalyzed E/diene copolymerization and E/diene/1-hexene and E/diene/propylene terpolymerizations, and the quantitative relationship between diene structure and polymer chain propagation rate constant in term of quantifiable catalytic active sites. One of the most important but unknown factors in olefins ansa-zirconocene complexes is the distribution of the catalyst between sites actively participating in polymer chain formation and dormant sites. A set of ethylene/dienes copolymerizations, and ethylene/dienes/1-hexene and ethylene/dienes/1-hexene terpolymerizations catalyzed with ansa-zirconocenes/borate/triisobutylaluminium (rac-Et(Ind)2ZrCl2/[Ph3C][B(C6F5)4]/triisobutylaluminium (TIBA) were performed in toluene at 50 °C To determine the active center [C*]/[Zr] ratio variation in the copolymerization of E with different dienes and their terpolymerization with 1-hexene and propylene, each polymer propagation chain ends were quenched with 2-thiophenecarbonyl, which selectively quenches the metal–polymer bonds through acyl chloride. The ethylene, propylene, 1-hexene, and diene composition-based propagation rate constants (kpE, kpP, kp1-H, and kpdiene), thermal (melting and crystalline) properties, composition (mol% of ethylene, propylene, 1-hexene, and diene), molecular weight, and polydispersity were also studied in this work. Systematic comparisons of the proportion of catalytically [Zr]/[C*] active sites and polymerization rate constant (kp) for ansa-zirconocenes catalyzed E/diene, E/diene/1-hexene, and E/diene/propylene polymerization have not been reported before. We evaluated the addition of 1-hexene and propylene as termonomers in the copolymerization with E/diene. To make a comparison for each diene under identical conditions, we started the polymerization by introducing an 80/20 mole ratio of E/P and 0.12 mol/L of 1-hexene in the system. The catalyst behavior against different dienes, 1-hexene, and propylene is very interesting, including changes in thermal properties, cyclization of 1-hexene, and decreased incorporation of isoprene and butadiene, changes in the diffusion barriers in the system, and its effect on kp.

Design of Self-Healing EPDM/Ionomer Thermoplastic Vulcanizates by Ionic Cross-Links for Automotive Application.

The development of smart elastomeric materials with inherent self-repairing abilities after mechanical damage has important technological and scientific implications, particularly in regard to the durability and life cycle of rubber products. The interest in self-healing materials for automotive applications is rapidly growing along with the increasing importance of vehicle scratch quality and quantity. The creation of a reversible network by noncovalent ionic cross-linking in elastomer/rubber blends is an effective approach to generate the self-healing phenomenon, with reprocessing and recycling properties. In this work, thermoplastic vulcanizates (TPVs) were prepared using ethylene–propylene–diene (EPDM) polymers and high-acid-containing thermoplastic ionomers. Along with the general EPDM, maleic anhydride grafted EPDM (EPDM-g-MAH) was also used for the preparation of the TPVs. The strategy was based on a simple ionic crosslinking reaction between the carboxyl groups present in the ionomer and zinc oxide (ZnO), where the formation of reversible Zn2+ salt bondings exhibits the self-healing behavior. The heterogeneous blending of EPDM and ionomers was also used to investigate the thermal and mechanical properties of the TPVs. The experimental findings were further supported by the surface morphology of the fracture surfaces viewed using microscopy. The self-healing behavior of the TPVs has been identified by scratch resistance testing, where the EPDM-g-MAH TPVs showed excellent healing efficiency of the scratch surface. Therefore, this work provides an efficient approach to fabricate new ionically cross-linked thermoplastic vulcanizates with excellent mechanical and self-repairing properties for the skins of automotive interior door trims and instrument panel applications.

Metal-Free Hydrosilylation Polymerization by Merging Photoredox and Hydrogen Atom Transfer Catalysis.

Organosilicon compounds and polymers have found wide applications as synthetic building blocks and functional materials. Hydrosilylation is a common strategy toward the synthesis of organosilicon compounds and polymers. Although transition-metal-catalyzed hydrosilylation has achieved great advances, the metal-free hydrosilylation polymerization of dienes and bis(silane)s, especially the one suitable for both electron-rich and electron-deficient dienes, is largely lacking. Herein, we report a visible-light-driven metal-free hydrosilylation polymerization of both electron-rich and electron-deficient dienes with bis(silane)s by using the organic photocatalyst and hydrogen atom transfer (HAT) catalyst. We achieved the well-controlled step-growth hydrosilylation polymerizations of the electron-rich diene and bis(silane) monomer due to the selective activation of Si-H bonds by the organic photocatalyst (4CzIPN) and the thiol polarity reversal reagent (HAT 1). For the electron-deficient dienes, hydrosilylation polymerization and self-polymerization occurred simultaneously in the presence of 4CzIPN and aceclidine (HAT 2), providing the opportunity to produce linear, hyperbranched, and network polymers by rationally tuning the concentration of electron-deficient dienes and the ratio of bis(silane)s and dienes to alter the proportion of the two polymerizations. A wide scope of bis(silane)s and dienes furnished polycarbosilanes with high molecular weight, excellent thermal stability, and tunable architectures.

Species on the Activated TiCl4/MgCl2 Pre-catalyst for Diene Polymerizations

Species on the Activated TiCl4/MgCl2 Pre-catalyst for Diene Polymerizations

Access to Highly Stereodefined 1,4-cis-Polydienes by a [Ni/Mg] Orthogonal Tandem Catalytic Polymerization.

A [Ni/Mg]-catalyzed orthogonal tandem polymerization has been developed starting from enol phosphates. Initial investigations conducted on branched 1,3-dienes as monomers enabled identification of a Mg-initiated polymerization process leading to 1,4-cis-polydienes. When aryl enol phosphates are used as monomers, the [Ni/Mg]-catalyzed tandem polymerization affords 1,4-cis-polydienes with selectivities up to 99%. Elastomeric or crystalline materials were obtained by simple structural modifications of the monomeric unit. This tandem approach appears as a straightforward and efficient way to enforce diversity and selectivity in diene polymerization while retaining a fair degree of control, just as observed for stepwise systems that are accessible through established time- and manpower-consuming synthetic procedures.

Copper-Catalyzed Highly Enantioselective 1,4-Protoboration of Terminal 1,3-Dienes

Copper-Catalyzed Highly Enantioselective 1,4-Protoboration of Terminal 1,3-Dienes

Dienes Polymerization: Where We Are and What Lies Ahead

Recently, the research activity in the field of the stereospecific polymerization of conjugated dienes has focused on the use of catalysts based on organometallic complexes having a well-defined structure and containing ligands of various types (e.g., phosphines, bis-imines, and pyridylimines), since it has been observed that the nature of the ligand, as expected on the basis of the diene polymerization mechanism proposed several years ago by Porri, is able to exert a strong influence on the polymerization regio- and stereoselectivity, on the polymer molecular weights and their distribution, and in some cases to impart a living feature to the catalysts themselves. In this Perspective we highlight the most recent results obtained in this field and discuss possible future developments in this area.

Nanocatalysts in Olefins and Dienes Polymerization Processes

Sustainable development, the design of green and economically feasible processes to produce synthetic polymers is one of the major needs and biggest challenges. Catalysis of polymerization processes is among the most important applications within the field of nanoscience. Intensive research is being conducted and considerable success has been achieved in the heterogenization of various homogeneous catalysts on nano supports for polymerization of olefins and dienes. The large surface area of various nanomaterials qualifies them quite naturally to act either as a heterogeneous promoter for catalytic reactions or as a support for the heterogenization of homogeneous catalysts. To the polymerization of olefins and dienes by using nanocatalysts are devoted significant numbers of published papers, but to elucidate the possible effect of both the type and properties of nano supports and their sizes and amounts on the activity and stereoselectivity of heterogenized catalysts and the properties of the obtained polymers are needed more detailed studies. This review attempted to collect some published research materials in the field of the nanocatalysis of olefins and dienes polymerization processes and our main aim is to assess the critical points and to indicate the future perspectives and possible strategies in this area of research. We are confident that this review will be a helpful companion and deliver key hints to those, in academia and in the industry, who decide to move their research interest in this direction

About building a basis surface in inverse kinetic problems for non-break processes of diene polymerization

The work contains a mathematical description of diene polymerization with a neodym-based Ziegler-Natta catalysts. The resulting system of differential equations was reduced from infinite to finite by the method of moments. For this, the basis of nonlinear parametric functions was searched with a method allowing obtain expressions that reflect the kinetics of the polymerization process. The obtained basis of two functions enables us to construct a surface containing local regions of the minimum of the objective function which define the starting points for search of optimum kinetic constant values.

Dienes and diamondoids: poly(2‐[1‐adamantyl]‐1,3‐butadiene) and random copolymers with isoprene via redox‐emulsion polymerization and their hydrogenation

AbstractA novel route to adamantane substituted diene copolymers is demonstrated using emulsion polymerization, with an improved monomer synthesis. Heterogenous dehydration of 2‐(1‐adamantyl)‐3‐buten‐2‐ol using Amberlyst®‐15 cationic exchange resin at ambient temperature gave 2‐(1‐adamantyl)‐1,3‐butadiene (1) in excellent yield and presents an attractive alternative monomer synthesis route. Emulsion polymerization of 1 and mixtures of 1 and isoprene was carried out at room temperature using redox pair, hydroperoxide initiator. All poly(1) and poly(1‐ran‐isoprene) samples were soluble in common organic solvents and exhibited high 1,4‐microstructure. A continuous increase in glass transition temperature from −63 to 172°C was observed by increasing the ratio of 1 in the comonomer feed of poly(1‐ran‐isoprene), and Tg values were in good agreement with the Fox equation. After complete hydrogenation to poly(1‐vinyladamantane‐alt‐ethylene‐ran‐propylene‐alt‐ethylene), a continuous increase in Tg was observed from −55 to 152°C. The high solubility and improved access to 2‐(1‐adamantyl)‐1,3‐butadiene opens the door to exploration of diene polymers with enhanced high temperature properties.