Norbornene Units Research Articles

Influence of the Norbornene Anchor Group in Ru-Mediated Ring-Opening Metathesis Polymerization: Synthesis of Bottlebrush Polymers

Ring-opening metathesis polymerization (ROMP) mediated by Grubbs’ third-generation catalyst [G3, (H2IMes)(Cl)2(pyr)2RuCHPh] is widely used to make bottlebrush polymers by polymerization of a macromonomer (MM), typically a low molecular weight polymer functionalized with a norbornene. Termed the grafting-through method, this strategy requires a high degree of living character (“livingness”) to form well-defined bottlebrush polymers. Here, we studied how various anchor groups, the series of atoms connecting the polymerizable norbornene unit to the polymer side-chain, affect livingness in ROMP in a series of exo-norbornene polystyrene MMs. First, we calculated the HOMO and HOMO/LUMO gap energies of MM structures containing five different anchor groups using density functional theory methods, finding that these energies spanned a range of 10 kcal/mol. We then performed kinetics experiments on each MM with target backbone degrees of polymerization (Nbb) of 100 to measure the propagation rate constant (kp,obs) under identical conditions. A positive correlation between the HOMO energy and measured kp,obs values emerged, revealing a 7-fold variation in kp,obs values across the five MMs, suggesting different degrees of livingness among the anchor groups. A series of studies targeting Nbb values ranging from 100 to 2000 further highlighted these differences: The MMs with high kp,obs values reached higher conversions at high target Nbb values with lower dispersities (D̵) than the MMs with lower kp,obs values. Finally, we evaluated the synthesis of bottlebrush pentablock copolymers using the MMs at the two extremes by injecting an MM aliquot into a catalyst solution five consecutive times, allowing for polymerization of each block before the next injection. MM conversion at each step was higher, and the D̵ values for each block were lower for the MM with the highest kp anchor group compared to the lowest kp anchor group. Taken together, these studies highlight how the anchor group dramatically affects both kp and livingness in ROMP, which is crucial for the synthesis of precise bottlebrush (co)polymers.

Influence of the Norbornene Anchor Group in Ru-Mediated Ring-Opening Metathesis Polymerization: Synthesis of Linear Polymers

Ring-opening metathesis polymerization (ROMP) mediated by Grubbs’ first-generation catalyst [G1, (PCy3)2(Cl)2RuCHPh] and Grubbs’ third-generation catalyst [G3, (H2IMes)(Cl)2(pyr)2RuCHPh] can exhibit living characteristics for some monomer classes, most commonly substituted norbornenes. Here, we studied how various anchor groups, the series of atoms connecting the polymerizable norbornene unit to a functional group, affect livingness in ROMP in a series of small-molecule exo-norbornene monomers. We first designed and calculated the HOMO energy of 61 monomers using density functional theory methods, finding that these energies spanned a range of 25 kcal/mol. We then performed kinetics experiments using 1H NMR spectroscopy to measure the propagation rate constant (kp,obs) under identical conditions for eight selected monomers with different anchor groups across the range of HOMO energies. We observed a positive correlation between the HOMO energy or the HOMO/LUMO energy gap and measured kp,obs values for both catalysts, revealing a 30-fold and a 10-fold variation in kp,obs values across the series for G1 and G3, respectively. Interestingly, we observed a plateau for the three monomers with the highest HOMO energies for G3 catalyst, suggesting that above a certain level, the HOMO energy no longer influenced the rate-determining step under the conditions studied here. Chelation studies revealed that only one of the eight monomers showed measurable binding of electron-rich groups on the monomer to the catalyst, but with no apparent effect on kp. Finally, we utilized 1H NMR spectroscopy to measure the rate of catalyst decomposition in the presence of each monomer, a key termination pathway in ROMP. Ultimately, we determined that the anchor group did not substantially affect catalyst decomposition, a proxy for the termination rate constant (kt). In sum, these combined computational and experimental studies collectively demonstrate that livingness in ROMP of exo-norbornene monomers using G1 and G3 catalysts, as measured by relative kp/kt ratios, is primarily controlled by the kp of the anchor group, which is correlated with the HOMO energy.

Hydrophobic cyclic dipeptides as M+/Cl- carriers.

Transmembrane ion-pair co-transport using synthetic transporters is non-trivial. Herein, cyclic dipeptide ion-carriers with dangling ester motifs to bind cations and amide-NH to bind anions are reported. The pendant lipophilic norbornene units aid in membrane insertion to achieve MCl co-transport with this simple design.

Synthesis of photoactive nanocomposite hydrogels via in-situ photoinitiated thiol-ene click polymerization of acrylates containing norbornene-POSS and norbornene-POSS/Ag NPs

Radical-mediated thiol-ene photopolymerization is a method that has been studied intensively since the beginning of the century due to the nature of click chemistry which can be carried out in a fast, controllable, and easy way under mild environment conditions with no or minimal formation of by-products. In order to improve the properties of the polymeric nanocomposite materials which have been obtained by photopolymerization method and to prepare them for a particular purpose, various nano-sized photo-reactive groups or cross-linking agents have been added to the formulations. The advantage of this study for the preparation of thin-film and hydrogel nanocomposites is based on one-pot thiol-ene photo-click polymerization. The main contribution made by one-component Type II photoinitiator, 2-Mercaptothioxanthone (TX-SH) carries both thiol functionality and chromophoric group on it. Polyhedral oligomeric silsesquioxane (POSS) functionalized with 1 or 3 norbornene units was used as alkene and played a good role in the preparation of nanocomposite hydrogels with/without in-situ formed silver nanoparticles (Ag NPs) with various acrylate content by thiol-ene photo-click polymerization. Especially the good contribution of norbornenylethyl disilanol isobutyl polyhedral oligomeric silsesquioxane (1NBPOSS) or tris-norbornenyl isobutyl polyhedral oligomeric silsesquioxane (3NBPOSS) was seen in terms of conversion percentage of acrylates which was determined by photo differential scanning calorimetry (photo-DSC) and swelling ratios of hydrogels in phosphate buffer solution (PBS) buffer solution. Besides them, obtained nanocomposites displayed good thermal stability values according to the Thermogravimetric analysis (TGA) measurements and scanning electron microscopy (SEM) images confirmed rather small-sized and uniform in-situ formed Ag NPs.

Cationic Copolymers of Norbornylized Seed Oils for Fiber-Reinforced Composite Applications.

Norbornylized seed oils, i.e., norbornylized linseed oil (NLO), norbornylized soybean oil (NSO), and norbornylized high oleic soybean oil (NHOSO), were synthesized via the Diels–Alder reaction of seed oil and dicyclopentadiene (DCPD) at high temperature (∼235 °C) and high pressure (∼80 psi), followed by cationic copolymerization using DCPD with boron trifluoride diethyl etherate catalyst. Norbornylized seed oils were characterized using H1 nuclear magnetic resonance (NMR), attenuated total reflectance-Fourier transform infrared, and gel permeation chromatography (GPC). Copolymers were formulated with four different DCPD contents, and curing was investigated using dynamic differential scanning calorimetry (DSC) measurements. It was found that the curing followed NLO > NSO > NHOSO with NLO having the highest exotherm, lowest activation energy, and lowest onset temperature. Furthermore, the gelation times were the least for NLO-DCPD copolymers. As anticipated, the degree of unsaturation and norbornene moieties strongly influenced the curing of copolymer thermosets. The copolymer products were compression-molded into thermosets and characterized by DSC, Soxhlet extraction, thermogravimetric analysis (TGA), H1 NMR, solid-state C13 NMR, and GPC. NLO-DCPD thermosets demonstrated high cure, higher thermal stability, glass transition temperature, and cross-linking capability compared to the other seed oil-DCPD counterparts. NMR and GPC results further suggested that bis-allylic and norbornene units concomitantly participated very actively during the cationic curing reaction. Moreover, scanning electron microscopy images of glass fiber-reinforced NLO-DCPD copolymer composites demonstrated good interfacial adhesion between the polymer matrix and fiber phases, imparting enhanced thermo-mechanical properties. This research opens a new venue for higher biobased greener polymer constituent for composite applications.

Unsaturated Copolyesters from Macrolactone/Norbornene: Toward Reaction Kinetics of Metathesis Copolymerization Using Ruthenium Carbene Catalysts

Unsaturated copolyesters are of great interest in polymer science due to their broad potential applications and sustainability. Copolyesters were synthesized from the ring-opening metathesis copolymerization of ω-6-hexadecenlactone (HDL) and norbornene (NB) using ruthenium-alkylidene [Ru(Cl2)(=CHPh)(1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)(PCy3)] (Ru1), [Ru(Cl)2(=CHPh)(PCy3)2] (Ru2), and ruthenium-vinylidene [RuCl2(=C=CH(p-C6H4CF3))(PCy3)2] (Ru3) catalysts, respectively, yielding HDL-NB copolymers with different ratios of the monomer HDL in the feed. The activity of N-heterocyclic-carbene (NHC) (Ru1) and phosphine (Ru2 and Ru3) ligands containing ruthenium-carbene catalysts were evaluated in the synthesis of copolymer HDL-NB. The catalysts Ru1 with an NHC ligand showed superior activity and stability over catalysts Ru2 and Ru3 bearing PCy3 ligands. The incorporation of the monomers in the copolymers determined by 1H-NMR spectroscopy was similar to that of the HDL-NB values in the feed. Experiments, at distinct monomer molar ratios, were carried out using the catalysts Ru1–Ru3 to determine the copolymerization reactivity constants by applying the Mayo–Lewis and Fineman–Ross methods. The copolymer distribution under equilibrium conditions was studied by the 13C NMR spectra, indicating that the copolymer HDL-NB is a gradient copolymer. The main factor determining the decrease in melting temperature is the inclusion of norbornene units, indicating that the PNB units permeate trough the HDL chains. The copolymers with different molar ratios [HDL]/[NB] have good thermal stability up to 411 °C in comparison with the homopolymer PHDL (384 °C). Further, the stress–strain measurements in tension for these copolymers depicted the appreciable increment in stress values as the NB content increases.

Synthesis of Angular Triquinane and [4.3.3]Propellane Derivatives via Ring‐Rearrangement Olefin Metathesis

AbstractHerein, a simple and useful approach to angular triquinane and [4.3.3]propellane moieties is described via olefin metathesis starting from exo and endo Diels‐Alder (DA) adducts containing norbornene unit. This approach involves DA reaction, and ring‐rearrangement metathesis (RRM) as key steps. Strained norbornene derivatives on allylation at bridgehead position(s) followed by ring‐opening metathesis and ring‐closing metathesis sequence delivered angular triquinane and also stereochemically different propellane derivatives.

Multiblock Copolymers of Norbornene and Cyclododecene: Chain Structure and Properties.

We investigate the structure–property relations of the multiblock copolymers of norbornene with cyclododecene synthesized via the macromolecular cross-metathesis reaction between amorphous polynorbornene and semicrystalline polydodecenamer in the presence of the first-generation Grubbs catalyst. By adjusting the reaction time, catalyst amount, and composition of the initial system, we obtain a set of statistical multiblock copolymers that differ in the composition and average length of norbornene and dodecenylene unit sequences. Structural, thermal, and mechanical characterization of the copolymers with NMR, XRD, DSC (including thermal fractionation by successive self-nucleation and annealing), and rotational rheology allows us to relate the reaction conditions to the average length of crystallizable unit sequences, thicknesses of corresponding lamellas, and temperatures of their melting. We demonstrate that isolated dodecenylene units can be incorporated into crystalline lamellas so that even nearly random copolymers should retain crystallinity. Weak high-temperature endotherms observed in the multiblock copolymers of norbornene with cyclododecene and other cycloolefins could indicate that the corresponding systems are microphase-separated in the melt state.

Functional polyesters via the regioselective ring-opening copolymerizations of norbornene anhydride with epichlorohydrin

The highly regioselective ring-opening copolymerizations of 5-norbornene-2,3-dicarboxylic anhydride (NA) and epoxide monomers have been successfully achieved using CrIII catalyst bearing tetradentate imine-thioether-bridged bis(phenolate) ligand in combination with bis(triphenylphosphine)iminium chloride. The cis/trans regioselectivity of resulting polyesters can be tailored simply by controlling the feed ratio and the structure of monomer. Specifically, the polyesters produced by the copolymerization of NA and epichlorohydrin offer a robust platform for the post-modification. Thus, the ring-strained CC double bonds in the norbornene units promote the azide-alkene 1,3-dipolar cycloaddition to functionalize the resulting polyesters depending on targets.

Benzoquinone- and Naphthoquinone-Bearing Polymers Synthesized by Ring-Opening Metathesis Polymerization as Cathode Materials for Lithium-Ion Batteries.

Organic electrode materials have attracted great interest for next-generation lithium-ion batteries owing to their merits of low cost, resource sustainability, and environmental friendliness. Dissolution in organic electrolyte is one of critical factors that limit their development, and constructing corresponding polymers is an effective way to prevent it. Herein, the synthesis of benzoquinone- and naphthoquinone-bearing polymers by ring-opening metathesis polymerization of monomers with an exo-type four-membered ring between polymerizable norbornene and redox-active quinone units is reported. They exhibit significantly reduced solubility and clearly enhanced electrochemical performance. In particular, a high capacity (189.7 mAh g-1 at 0.1 C, 1 C=216.1 mA g-1 ), stable cycling (75.6 % capacity retention after 500 cycles at 2 C), and good rate capability (retaining 80.4 % from 0.1 to 2 C) were obtained for the naphthoquinone-bearing polymer, which stand out among naphthoquinone-bearing polymer electrode materials. This work offers rational molecular design and a new polymerization strategy to construct high-performance polymer electrode materials.

Cyclododecene in Olefin Metathesis: Polymerization and Macromolecular Cross-Metathesis with Polynorbornene

The reaction of macromolecular cross-metathesis of polynorbornene and polydodecenamer catalyzed by the first-generation Grubbs Ru-carbene complex is studied for the first time. Polydodecenamer with high-molecular-weight characteristics (Mw = 406 × 103, Ð = 2.5) and a yield of 96% is synthesized by the ring-opening metathesis polymerization of cyclododecene mediated by the second-generation Grubbs catalyst. The polymer has a melting temperature of 62–83°C, depending on the content of trans double bonds, and shows poor solubility in organic solvents at room temperature. Its cross-metathesis with polynorbornene at 40°С gives rise to new statistical multiblock copolymers of norbornene and cyclododecene with different degree of blockiness. NMR, GPC, and DSC were used to investigate the effect of reaction conditions on the structure and thermal properties of the copolymers. At the initial step of the reaction, along with a high-molecular-weight peak, the GPC chromatograms exhibit a peak due to the low-molecular-weight fraction (M = (1–2) × 103), suggesting the formation of cyclooligomers. With increasing degree of interchain exchange, the proportion of the oligomeric fraction decreases appreciably. The kinetics of the cross-metathesis of polynorbornene with polydodecenamer and polyoctenamer at 40°С is studied by in situ 1Н NMR spectroscopy and ex situ 13С NMR spectroscopy. The rates of elementary reactions in these blends differ insignificantly, except for the conversion stage of the initial carbenes into polymer ones. The formation rate for carbene [Ru]=polyoctenamer is three times higher than the formation rate for the [Ru]=polydodecenamer carbene. In both cases, the fraction of Ru carbenes attached to norbornene units is extremely small throughout the process.

Copolymerization of 1,3-butadiene and norbornene catalyzed by Ni complexes [1

(bpy)NiBr2 catalyzes the copolymerization of butadiene and norbornene (56:44) in the presence of methylaluminoxane at 30 °C. 1H NMR spectrum of the copolymer contains signals of norbornene units and 1,4-butadiene units and shows the molar ratio of the two monomer units to be 56:44. Copolymerization with a higher portion of norbornene monomer catalyzed by (bpy)NiBr2 affords a solid copolymer rich in norbornene unit, whereas the copolymerization with a higher portion of butadiene forms an oily copolymer rich in butadiene unit. Composition of the monomer units of the copolymer in terms of butadiene/norbornene ratio varies from 12:88 to 91:9, depending on the initial ratio of the monomers; this finding is different from the previous results obtained using Ni catalyst.

Domino ring-opening-ring-closing enyne metathesis vs enyne metathesis of norbornene derivatives with alkynyl side chains. Construction of condensed polycarbocycles.

The metathesis of norbornene derivatives with alkynyl side-chain with Grubbs’ ruthenium alkylidine as catalyst has been investigated with the objective of constructing condensed polycyclic structures. This investigation demonstrated that the generally observed domino reaction course involving a ring-opening metathesis of the norbornene unit and a ring-closing enyne metathesis is influenced to a great extent by the nature of the functional group and the substrate structure and may follow a different reaction course than what is usually observed. In cases where ROM–RCEYM occurred, the resulting 1,3-diene reacts in situ with the dienophile to provide condensed tetracyclic systems.

Templated Ring-Opening Metathesis (TROM) of Cyclic Olefins Tethered to Unimolecular Oligo(thiophene)s

We developed a fully abiotic approach to template the synthesis of discrete unimolecular polyolefins. Discrete, unimolecular oligo(thiophene)s with alternating sequence were obtained by iterative convergent/divergent couplings and then functionalized with pendant cyclic olefin monomers in the side chains. Upon treatment with the Grubbs third-generation catalyst in dilute solution (0.15 mM in DCM at 0 °C), the pendant monomers undergo templated ring-opening metathesis (TROM). Then, the daughter olefin is liberated from the parent thiophene by hydrolysis. Cyclooctenes undergo TROM to afford macrocyclic products that exactly replicate the chain length of the parent oligomer, as evidenced by MALDI MS/MS and NMR. Norbornene derivatives also undergo TROM and replicate unimolecular chain lengths, but in contrast, they exclusively form the linear oligomeric products with styrenic end groups. A template that was functionalized with one norbornene unit at the α chain end, followed by five cyclooctene units along th...

Facile Synthesis of Optically Active and Thermoresponsive Star Block Copolymers Carrying Helical Polyisocyanide Arms and Their Thermo-Triggered Chiral Resolution Ability.

A left-handed helical poly(phenyl isocyanide) bearing a norbornene unit and a Pd(II) complex on each terminus was prepared. The norbornene terminus was core cross-linked with a bisnorbornene linker via ring-opening metathesis polymerization (ROMP), yielding a star polymer carrying left-handed helical arms decorated with Pd(II) units at the exterior. The optical activities of the helical arms were maintained after the cross-linking reaction. The Pd(II) units on the surface of the star polymer were chain extended with a new phenyl isocyanide bearing three hydrophilic triethylene glycol monomethyl chains, which afforded an amphiphilic star block copolymer carrying helical arms. Such a star block copolymer showed excellent thermoresponsiveness with the lower critical solution temperature (LCST) around 55 °C. This optically active and thermoresponsive star polymer can enantioselectively capture the S-enantiomer of racemic methyl benzyl alcohol solution at a temperature lower than the LCST and precipitated when the temperature was higher than the LCST, leaving the R-enantiomer in the solution. The enantiomeric excess (ee) of the isolated enantiomer is up to 75%.

Kinetic study on the thermal degradation of ethylene–norbornene copolymers under the effect of Fe and Mn stearates

A kinetic study on the thermal degradation of ethylene–norbornene cyclic olefin copolymers (COCs), pristine and formulated with iron and manganese stearate, was performed. Three different COCs with cyclic structure (norbornene) contents of 30 mol% (COC30), 38 mol% (COC38), and 55 mol% (COC55) were analyzed. The thermal degradation order (n), activation energy (E a), and pre-exponential factor (A) were evaluated using multiple heating rates based on three different “model-free” methods: Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose (KAS) and Friedman (FR). The thermal stability of virgin and formulated COC films with ferric and manganese stearates were calculated using a non-isothermal thermogravimetric analysis (TGA) and derivative thermogravimetric analysis. The reaction order of the thermodegradation of the tested copolymers was close to unity according to the KAS and FR methods. The calculated E a for pristine copolymers increased from 232 to 254 kJ mol−1 when the content of cyclic norbornene units in the pure copolymers was diminished from 55 to 30 mol%. The calculated E a for the stearate-formulated COC copolymers had values between 214 and 238 kJ mol−1. TGA curves of the thermal degradation in a nitrogen atmosphere show a one-step reaction in the range of temperatures between 30 and 600 °C. It was found that manganese stearate is more efficient than ferric stearate in initiating the thermodegradation of COC38 and COC55 copolymers.

Unexpected regioselectivity observed in the bromination and epoxidation reactions of p-benzoquinone-fused norbornadiene: An experimental and computational study

The bromination reaction of p-benzoquinone-fused norbornadiene was studied at various temperatures (−78, −50, 0, 25, and 77 °C). At room temperature, the double bonds of the p-benzoquinone units were mainly brominated. The double bond of the norbornene unit also underwent a bromination reaction in a yield of only 2%. However, the reaction at −78 °C resulted in the formation of products derived from the attack of bromine on the norbornene double bond with higher charge density. In contrast to the bromination reaction, the epoxidation reaction of the same compound with m-chloroperbenzoic acid and dimethyldioxirane exclusively resulted in the formation of products derived from the addition to the double bond of norbornadiene. The regioselectivity observed was investigated and the results were supported by theoretical calculations.

Robust carboxylated polymer pores from a cyclic peptide template

Functionalized pores that are stable to chemical degradation are attractive for use in a variety of applications ranging from sensing to catalysis. Herein, robust polymer nanotube bundles decorated with carboxylate groups inside the pores have been developed in two steps from a cyclic peptide template containing polymerizable norbornene units. The cyclic peptide forms nanotube bundles of ca. 35 nm in diameter. Polymerization of the exposed norbornene units gives peptide–polymer hybrid nanotube bundles of ca. 100 nm diameter that have improved thermal and chemical stability compared to cyclic peptide nanotubes. Hydrolysis of the ester linkage connecting norbornene to the peptide scaffold and removal of the peptide provide robust polymer pores of ca. 100 nm that are not only chemically stable, but also have carboxylate groups in the pores. Such nanotube bundles with carboxylate groups can be potentially used for encapsulation of cations or biomimetic ion transport.

One-Pot Synthesis of Brush Copolymers Bearing Stereoregular Helical Polyisocyanides as Side Chains through Tandem Catalysis

An air-stable phenylethynyl Pd(II) complex containing a polymerizable norbornene unit was designed and synthesized. Such a Pd(II) complex can initiate the living/controlled polymerization of phenyl isocyanide, giving stereoregular poly(phenyl isocyanide)s in high yields with controlled molecular weights and narrow molecular weight distributions. The norbornene unit on the Pd(II) complex can undergo ring-opening metathesis polymerization (ROMP) with Grubbs’ second-generation catalyst, affording polynorbornene bearing Pd(II) complex pendants under a living/controlled manner. Interestingly, the Pd(II) complex pendants on the isolated polynorbornene are active enough to initiate the living/controlled polymerization of phenyl isocyanides, yielding well-defined brush-like copolymers with polynorbornene backbone and helical poly(phenyl isocyanide) as side chains. 31P NMR analyses indicate almost all the Pd(II) units on the polynorbornene participated in the polymerization, and the grafting density of the brush copolymer is high. Further studies revealed the brush copolymer can be readily achieved in one-pot via tandem catalysis. By using this method, a range of brush copolymers with different structures and tunable compositions were facilely prepared in high yields with controlled molecular weights and narrow molecular weight distributions. The synthesized brush copolymers were revealed to form worm-like cylindrical morphologies and helical rod architectures in film state by atomic force microscope observations.

Photoresponsive Gels Prepared by Ring‐Opening Metathesis Polymerization

This communication describes photoresponsive gels, prepared using ring-opening metathesis polymerization (ROMP), that dissolve upon irradiation with ultraviolet light. Exposure of mixtures of norbornene-type ROMP monomers and new photoreactive cross-linkers comprising two norbornene units bound through a chain containing o-nitrobenzyl esters (NBEs) to well-known ruthenium carbene catalysts gave cross-linked polymer networks that swelled in organic solvents or water depending on the structure of the monomer. These gels became homogeneous upon irradiation with UV light, consistent with breaking of the cross-links through photolysis of the NBE groups. The irradiation time required for homogenization of the gels depended on the cross-link density and the structure of the photoresponsive cross-linker.