Ring-opening Metathesis Polymerization Of Norbornene Research Articles

ROMP of norbornene and oxanorbornene derivatives with pendant fluorophore carbazole and coumarin groups

A series of new (oxa)norbornene dicarboximide monomers, decorated with carbazole and coumarin as pendant fluorophore groups, were synthesized and characterized. Their behaviour in ring-opening metathesis polymerization (ROMP) was explored in the presence of commercial Grubbs’ third generation catalyst G3 and cis-selective catalyst GZ. Norbornene dicarboximide (NDI) monomers were successfully polymerized by both the catalysts, while oxanorbornene dicarboximide (ONDI) analogues showed scarce reactivity toward polymerization promoted by GZ. The nature of the spacer (ethylene or p-xylene) between the NDI unit and the chromophore seems to not affect the outcome of the polymerization. Moving from G3 to GZ, it was possible to synthetize NDI-based polymers with cis-olefin content increasing from 47 to 89%, depending on the nature of the pendant fluorophore group. The obtained polymers showed photoluminescence in solution and solid state owing to the carbazole or coumarin fragment, regardless of the nature of the spacer and cis-olefin amount. Interestingly, a significant excimer emission due to the overlap of carbazole groups was observed for a carbazole-functionalized polymer film, as a result of the combined effect of two factors, the stiffness of the spacer (p-xylene) linking the NDI moiety to the fluorophore and the high stereoregularity degree (83% cis) of the main chain.

Synthesis and characterization of a novel latent ring-opening metathesis polymerization catalyst

The synthesis and characterization of a novel latent ruthenium catalyst bearing a chelate ligand containing an oxadiazole fragment for the olefin metathesis are described. The main advantages of the utilization of this ligand are the straightforwardness of preparation, mild reaction conditions, and availability of the feedstock. Preliminary study of the catalytic activity of the Ru complex for metathesis reactions demonstrated its inactive nature for the ring-closing metathesis (RCM), but an excellent thermo-switchability for the ring-opening metathesis polymerization of norbornene.

Bi-functional side chain architecture tuned amphoteric ion exchange membranes for high-performance vanadium redox flow batteries

The blended amphoteric membranes possessed a reducing cation exchange capacity with increasing the anion exchange capacity. Bi-functional side-chain-type polymers are conducive to have both high cation exchange capacity and high anion exchange capacity at the same time, and further enhance ion conductivity of amphoteric ion exchange membranes (AIEMs). Herein, novel side-chain type AIEMs are prepared via ring-opening metathesis polymerization of norbornene possessing the advantages of yielding easily modified molecular architectures, simple and controllable polymerization, and producing the membranes with high chemical stability. To avoid the occurrence of excess water swelling arising from the increased zwitterionic groups, hydrophobic spacers (alkyl chain-(CH2)6 -) were introduced to be situated between the aromatic main chain and ionic groups. This unique structure favors ion clusters to be aggregated and thus forms highly ordered water channels so that the protons can be efficiently transported along the center of channels and possess excellent proton conductivity. In addition, the ion crosslinking interactions enhance the mechanical stability of AIEMs. The resultant AIEM (1/2) exhibits a higher ion conductivity of 7.58 × 10-2 S cm-1 and vanadium ion permeability of 0.21 × 10-9 cm2 s-1 at room temperature. Based on these good properties, the vanadium redox flow batteries (VRBs) with prepared membranes and Nafion 212 were tested. The energy efficiency (EE) of VRBs with AIEM (1/2) still reaches 84.76% at the current density of 160 mA cm-2, which is better than that with Nafion 212 (76.26%). Moreover, the EE of VRBs with AIEM (1/2) is 82.11% after 200 cycles, indicating that the prepared membranes possess a good stability.

Cationic tungsten imido alkylidene N-heterocyclic carbene complexes for stereospecific ring-opening metathesis polymerization of norbornene derivatives

Cationic W alkylidene N-heterocyclic carbene complexes allow for the stereospecific ring-opening metathesis polymerization of norbornenes with high trans-iso- and high cis-syndiospecificity, respectively.

Stereospecific Ring-Opening Metathesis Polymerization of Norbornene Catalyzed by Iron Complexes.

Developing well-defined iron-based catalysts for olefin metathesis would be a breakthrough achievement in the field not only to replace existing catalysts by inexpensive metals but also to attain a new reactivity taking advantage of the unique electronic structure of the base metals. Here, we present a two-coordinate homoleptic iron complex, Fe(HMTO)2 [HMTO=O-2,6-(2,4,6-Me3 C6 H2 )2 C6 H3 ], that is capable of performing ring-opening metathesis polymerization of norbornene to produce highly stereoregular polynorbornene (99 % cis, syndiotactic). The use of heteroleptic Fe(HMTO)(RO) [RO=(CH3 )2 CF3 CO, CH3 (CF3 )2 CO, or Ph(CF3 )2 CO] prepared in situ significantly increases the polymerization rate while preserving selectivity. The resulting polymers were characterized by 1 H and 13 C NMR spectroscopy and gel-permeation chromatography.

Synthesis of New of Norbornene–1,5-Bis(hexenyl)hexamethyltrisiloxane Copolymers via Olefin Metathesis Reaction

New copolymers of norbornene and 1,5-bis(hexenyl-5)-1,1,3,3,5,5-hexamethyltrisiloxane containing flexible siloxane and rigid norbornene fragments in the main chain are synthesized. Synthesis is carried out using three types of olefin metathesis reactions: the ring-opening metathesis polymerization of norbornene, the metathesis of nonconjugated diene 1,5-bis(hexenyl-5)-1,1,3,3,5,5-hexamethyltrisiloxane, and the interchain macromolecular cross-metathesis between polynorbornene and siloxane-containing polyene. The latter reaction is studied for the first time. With its help, new statistical multiblock copolymers of norbornene and 1,5-bis(hexenyl-5)-1,1,3,3,5,5-hexamethyltrisiloxane with different average block lengths are obtained and characterized by 1H and 13C NMR and IR spectroscopy. The effect of the copolymer structure on their thermal properties is investigated.

In situ-generated arene-ruthenium catalysts bearing cycloalkylamines for the ring-opening metathesis polymerization of norbornene

Arene-ruthenium complexes of type [RuCl2(p-cymene)(cyclo-alkylamine)], where alkyl is pentyl (1), hexyl (2), heptyl (3) or octyl (4), were successful synthetized and applied as pre-catalysts in ROMP of norbornene (NBE). From experiments as a function of temperature and NBE loads, the yields increased with increasing cyclo-alkyl ring size (4 >3 >2 >1). This was associated with steric-electronic features of the amine ligands. The highest yields of polyNBE were obtained with [NBE]/[Ru] molar reaction ratio = 5000/1 in the presence of EDA at 50 °C for 60 min, with molecular weight range of 3.6–5.9 × 104 g mol−1 and Ð of 1.6–2.3. Characterization data obtained from CHN elemental analysis, spectroscopic techniques (FTIR, UV–vis, and 1H- and 13C{1H} NMR), cyclic voltammetry, computational studies, and single crystal diffraction for complexes 2 and 4 were useful for understanding the pre-catalyst behavior. Thermodynamic parameters from DFT-calculation corroborate a ROMP process via a dissociative mechanism.

Synthesis of polypropylene-graft-norbornene by reactive extrusion and its rheological behavior

Abstract

Mechanosynthesis of Noels-type NHC–Ruthenium Complexes and Applications in Ring-Opening Metathesis Polymerization

The use of ball mills enabled the efficient mechanosynthesis of a variety of N-aryl,N-alkyl imidazolium salts and of corresponding NHC silver(I) complexes. Transmetalation with ruthenium via mechanochemistry allowed the rapid access (from 1.5 min to 1 h) to complexes having a similar structure to Noels-type precatalysts. Evaluation of the complexes in the ring-opening metathesis polymerization of norbornene in different solvent, including nontoxic ones, showed a high catalytic activity for one of them, comparable to that of the Noels catalyst.

Fac-[RuCl2(DMSO-S)3(n-butylamine)]: Synthesis, structural characterization and dual catalytic performance

The synthesis, spectroscopic properties and crystal structure of the novel complex fac-[RuCl2(DMSO-S)3(n-butylamine)] (DMSO-S = sulfur-bonded dimethylsulfoxide) have been reported. The coordination environment of the ruthenium atom is best described as a distorted octahedral, where three DMSO ligands occupy one face of the octahedron, while the two chlorido and the amine ligand occupy the other one. The catalytic activity of fac-[RuCl2(DMSO-S)3(n-butylamine)] was probed in two processes, ring-opening metathesis polymerization (ROMP) and atom-transfer radical polymerization (ATRP). The ROMP of norbornene (NBE) was carried out in the presence of ethyl diazoacetate (EDA) for 5 min at 50 °C which afforded yields around 80%. Poly(norbornadiene) was only produced by photoinduced ROMP leading to 27% yield. The catalytic activity for ATRP of methyl methacrylate (MMA) and styrene (St) for 8 h resulted in 88 and 33%, respectively.

Multiblock Anion Conducting Copolymers Based on Vinyl Addition and Ring-Opening Metathesis Polymerization of Norbornenes

Anion-exchange membranes (AEMs) have widespread applications in electrochemical devices. The development of AEMs with long-term alkaline stability and high hydroxide ion conductivity is currently of interest. The use of non-precious catalysts, facile reaction kinetics and reduced fuel crossover are some of the benefits over proton-exchange membranes (PEMs). However, the present limitations of AEMs include low ionic conductivity, poor stability at high pH, and high water uptake. A series of multiblock copolymers based on vinyl addition and ring-opening metathesis polymerization (ROMP) of norbornenes was synthesized for use in AEM fuel cells and electrolyzers (Scheme 1). The mechanical and thermal stability, ionic conductivity of both sets of polymers are discussed in detail. The long-term (>1200 h) alkaline stability results are promising. Financial support provided by the ARPA-E IONICS program for M.M. and G.H. is gratefully acknowledged. Figure 1

Polynorbornene-Based Anion Exchange Membranes for Alkaline Fuel Cells

Fuel cells based on alkaline exchange membranes (AEM) have garnered increased interest because of their inherent advantages over traditional proton exchange membranes (PEM). High pH operating conditions allow for more facile reaction kinetics, reduced platinum-group metal catalyst, and reduced fuel crossover issues. Moreover, these materials can be made from inexpensive precursors which can further drive down the cost of the membrane electrode assemblies (MEA) for fuel cells. In this study, a variety of block copolymer AEMs based on based on vinyl addition and ring-opening metathesis polymerization of norbornenes was synthesized and characterized. Correlations were found between the ionic conductivity and mechanical properties and the polymer structure, channel size and phase separation. The AEMs were also used to construct MEAs for alkaline fuel cells and their performance was analyzed using electrochemical impedance spectroscopy. Financial support provided by the ARPA-E IONICS program for G.H. and M.M. is gratefully acknowledged.

Ruthenium Carbene Complexes Analogous to Grubbs-I Catalysts Featuring Germylenes as Ancillary Ligands

Reactions of the first-generation Grubbs’ catalyst trans-[RuCl2(CHPh)(PCy3)2] (1) with the amidinatogermylenes Ge(tBu2bzam)R (R = tBu (L1), CH2SiMe3 (L2); tBu2bzam = N,N′-bis(tertbutyl)benzamidinate) have allowed the isolation and full characterization of the first specimens of Grubbs-type carbene complexes featuring heavier tetrylenes as ancillary ligands, namely, the disubstituted derivatives trans-[RuCl2(CHPh)(L1)2] (3) and cis-[RuCl2(CHPh)(L2)2] (7), which curiously differ in the arrangement of their germylene ligands. DFT calculations have revealed that the different volumes of L1 and L2 (the former is larger than the latter) are responsible for the different stereochemistry of 3 and 7. NMR-monitoring of the reaction solutions has allowed the observation of the monosubstituted intermediates trans-[RuCl2(CHPh)(L)(PCy3)] (L = L1 (2), L2 (5)) and their evolution to either the disubstituted final product (for L1) trans-[RuCl2(CHPh)(L1)2] (3) or the short-lived disubstituted intermediate (for L2) trans-[RuCl2(CHPh)(L2)2] (6). Complex 7 arises from a trans-to-cis isomerization of intermediate 6. As olefin metathesis catalysts, both 3 and 7 promoted the ring-closing metathesis of diethyl 2,2-diallylmalonate and the ring-opening metathesis polymerization of norbornene, but their catalytic activity decreased with the reaction time, indicating catalyst decomposition.

Using Ring-Opening Metathesis Polymerization of Norbornene To Construct Thermally Activated Delayed Fluorescence Polymers: High-Efficiency Blue Polymer Light-Emitting Diodes

The exploitation of blue polymer emitters is of great importance for the application of solution-processed organic light-emitting diodes (OLEDs) in full color display. The highly efficient blue thermally activated delayed fluorescence (TADF) polymers are rarely reported up to now. Herein, we report an efficient approach to construct blue TADF polymers by ring-opening metathesis polymerization (ROMP) of norbornene. By side-chain engineering strategy, the polymers are endowed with distinct TADF features. By use of these blue polymeric emitters, the nondoped OLEDs achieved a maximum external quantum efficiency of 7.3% with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.20, 0.29), which represents the state-of-the-art device performance for the TADF-based blue polymer light-emitting diodes (PLEDs).

Watching growth, step by step

Polymers Polymers can grow through the stepwise addition of monomers to an active end site. One might think that this would happen in a continuous linear process. With a focus on ring-opening metathesis polymerization of norbornene catalyzed by a Grubbs' catalyst, Liu et al. describe the growth of a single polymer chain. By attaching one end of a growing polymer to a bead exerting a constant force on it, they measured the extension occurring during the growth of the polymer. Oddly, the extension of the growing polymer did not increase continuously. Instead, it exhibited consecutive wait-and-jump steps, owing to conformational entanglements formed by newly incorporated monomers. Science , this issue p. [352][1] [1]: /lookup/doi/10.1126/science.aan6837

Non-carbene Complex [RuCl2(PPh3)2(azocane)] as Active Catalyst Precursor for ROMP and ATRP

The novel, non-carbene complex [RuCl2(PPh3)2(azocane)] (1) of trigonal bipyramid geometry was synthesized, characterized (CHN elementary analysis, FTIR, EPR, and 31P NMR), and applied as catalyst precursor for ring opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). ROMP of norbornene (NBE) resulted in 70% yield at 50 °C in 60 min, with [NBE]/[1] = 5000, and 15% yield from ROMP of norbornadiene was obtained under the same conditions. ATRP of methyl methacrylate (MMA) resulted in ca. 20% conversion at 85 °C in 9 h, with [MMA]/[1] = 1000, and increased to ca. 50% in the presence of Al(OiPr)3, with narrower PDI values. With [MMA]/[1] = 200, ca. 50% yield was obtained at 85 °C in 6 h either in the absence or presence of Al(OiPr)3. ATRP of styrene resulted in 9 and 16% conversion at 110 °C in 7 h in the absence or presence of Al(OiPr)3, respectively, with [St]/[1] = 1000. Results are discussed considering the five-coordinated molecular geometry of the starting complex and the arrangements required in ROMP and ATRP to initiate the reactions.

Synthesis of controlled, high-molecular weight poly(l-glutamic acid) brush polymers.

We report the synthesis and characterization of high-molecular weight poly(l-glutamic acid) based brush polymers. Utilizing a combination of ring-opening metathesis polymerization of norbornene based monomers and ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydride, high-molecular weight γ-benzyl protected poly(l-glutamic acid) brush polymers are synthesized. Controlled and complete deprotection of the benzyl groups using trimethylsilyl iodide resulted in poly(l-glutamic acid) based brush polymers with molecular weights up to 3.6 MDa, which may potentially be used to prepare size-controlled unimolecular polymeric nanomedicine for drug delivery applications. Camptothecin brush poly(l-glutamic acid) conjugates were prepared and their stability, drug release kinetics, and in vitro toxicity were studied.

Metathesis Polymerization Reactions Induced by the Bimetallic Complex (Ph4P)2[W2(μ-Br)3Br6

The reactivity of the bimetallic complex (Ph4P)2[W2(μ-Br)3Br6] ({W 2.5 W}7+, a′2e3) towards ring opening metathesis polymerization (ROMP) of norbornene (NBE) and some of its derivatives, as well as the mechanistically related metathesis polymerization of phenylacetylene (PA), is presented. Our results show that addition of a silver salt (AgBF4) is necessary for the activation of the ditungsten complex. Polymerization of PA proceeds smoothly in tetrahydrofuran (THF) producing polyphenylacetylene (PPA) in high yields. On the other hand, the ROMP of NBE and its derivatives is more efficient in CH2Cl2, providing high yields of polymers. 13C Cross Polarization Magic Angle Spinning (CPMAS) spectra of insoluble polynorbornadiene (PNBD) and polydicyclopentadiene (PDCPD) revealed the operation of two mechanisms (metathetic and radical) for cross-linking, with the metathesis pathway prevailing.

Synthesis of Alkyl and Alkylidene Complexes of Tungsten Bearing Imido and Redox-Active α-Diimine or o-Iminoquinone Ligands and Their Application as Catalysts for Ring-Opening Metathesis Polymerization of Norbornene

We report a new strategy to synthesize tungsten imido complexes bearing bidentate redox-active ligands through reduction of high-valent tungsten imido complexes by 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (abbreviated MBTCD) without forming any metal salt waste. Reaction of W(═NC6H3-2,6-iPr2)Cl4 and MBTCD in the presence of redox-active ligands, such as α-diimine and o-iminoquinone, produced tungsten imido complexes with the corresponding redox-active ligands, (α-diimine)W(═NC6H3-2,6-iPr2)Cl2 (1), [(o-iminoquinone)W(═NC6H3-2,6-iPr2)Cl]2(μ-Cl)2 (3), and (o-iminoquinone)W(═NC6H3-2,6-iPr2)Cl2(THF) (4), along with Me3SiCl and toluene as whole byproducts. Reaction of the brown complex 1 with [nBu4N][Cl] afforded intensely green single crystals of [nBu4N][(α-diimine)W(═NC6H3-2,6-iPr2)Cl3] (2). The versatile coordination modes of the α-diimine and o-iminoquinone ligands were clarified by spectroscopic methods and X-ray diffraction studies. Treatment of complex 1 with 1 equiv of Mg(CH2Ph)2·Et2O resulted in the formation of (α-diimine)W(═NC6H3-2,6-iPr2)(CH2Ph)2 (5), and thermolysis of 5 in the presence of PMe2Ph at 80 °C afforded the alkylidene complex (α-diimine)W(═NC6H3-2,6-iPr2)(═CHPh)(PMe2Ph) (6). On the other hand, thermolysis of 5 in the presence of CCl4 afforded the dissymmetric benzylidene complex (Cl3C-amido-imino)W(═NC6H3-2,6-iPr2)(═CHPh)Cl (7) via reductive cleavage of the C–Cl bond of CCl4. Isolated alkylidene complexes 6 and 7 served as catalysts for ring-opening metathesis polymerization of norbornene with 1 mol% of catalyst loading in toluene at 80 °C. Treatment of o-iminoquinone complex 4 with 2 equiv of LiCH2CMe2Ph afforded the dialkyl complex (o-iminoquinone)W(═NC6H3-2,6-iPr2)(CH2CMe2Ph)2 (8). Dialkyl complexes 5 and 8 at 80 °C served as catalysts to give poly(norbornene) with rather broad polydispersity.

Tuning the activity of alternative Ru-based initiators for ring-opening metathesis polymerization of norbornene and norbornadiene by the substituent in 4-CH2R-piperidine

The novel [RuCl2(PPh3)2(4-CH2R-pip)] complexes, with R=H (complex 1), Ph (2) or OH (3), were synthesized and applied as initiators for ROMP of norbornene (NBE) and norbornadiene (NBD) under different reaction times, temperatures and monomer concentrations. There is a clear difference in the homopolymer yields in the order 1>2>3 at [monomer]/[Ru] molar ratio of 5000, at 25°C for 5–60min. Difference in the yields tends to disappear at 50°C, with quantitative yields for 15–30min with any type of initiator. Results from copolymers obtained at RT for 60min from fixed amounts of NBE with four different amounts of NBD suggest that the type of initiator also affects the reactions, with more insertion of NBD with 1. The occurrence of cross-linking enhanced as the NBD loading increased, evidenced by decrease in the Mc and increase in the Tg values, besides the influence of the type of initiator.