Initiators For Ring-opening Metathesis Polymerization Research Articles

Grafting embedded poly(ionic liquid) brushes on biomimetic sharklet resin surface for anti-biofouling applications

In this work, we combined 3D printing technology and subsurface-initiated ring opening metathesis polymerization (ROMP) to construct a multi-scale brush-based antifouling surface. A biomimetic sharklet structured substrate embedded with ROMP initiator was prepared by 3D printing with commercial acrylic resin. Then, the embedded poly(ionic liquid) brushes were grafted onto the as-prepared biomimetic sharklet via subsurface-initiated ROMP of a novel ionic liquid monomer containing benzotriazole and imidazole groups ([BNIm][Br]). A series of characterization including infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscope proved the successful grafting of poly([BNIm][Br]) brushes on the as-prepared surface. X-ray photoelectron spectroscopy etching and friction tests demonstrated that poly([BNIm][Br]) can be grafted not only on the surface but on the subsurface of the as-prepared surface, and the as-prepared poly(ionic liquid) brush-based surfaces showed satisfactory wear resistance compared to traditional surface initiated ROMP. Subsequently, we evaluated the anti-biofouling properties of poly([BNIm][Br]) brushes. The results indicated that poly(ionic liquid) brushes can obviously resist adhesion of bovine serum albumin and have good anti-bacterial activity against both E. coli and S. aureus. The as-prepared poly(ionic liquid) brush-based biomimetic surface also exhibited considerable antifouling performance for microalgae (Porphyridium and Dunaliella) due to the synergistic effect of the surface composition and microstructure.

Decomposition of Vanadium(V) Alkylidenes Relevant to Olefin Metathesis

Vanadium alkylidenes can be highly active initiators for ring-opening metathesis polymerization of cyclic olefins; however, attempts to expand their use to cross metathesis have been unsuccessful d...

Metal-Free Preparation of Linear and Cross-Linked Polydicyclopentadiene

Metal-free ring-opening metathesis polymerization (ROMP) utilizes organic photoredox mediators as alternatives to traditional metal-based ROMP initiators to allow the preparation of polymers without residual metal contamination. Herein we report studies exploring the use of endo-dicyclopentadiene (DCPD), a common ROMP monomer, to form linear polyDCPD and copolymers with norbornene. Subsequent cross-linking of the linear polyDCPD using thiol-ene chemistry allows for a completely metal-free preparation of cross-linked polyDCPD. Furthermore, the examination of a number of structurally related monomers offers insights into mechanistic details of this polymerization and demonstrates new monomers that can be utilized for metal-free ROMP.

Engineering orthogonality in supramolecular polymers: from simple scaffolds to complex materials.

Owing to the mastery exhibited by Nature in integrating both covalent and noncovalent interactions in a highly efficient manner, the quest to construct polymeric systems that rival not only the precision and fidelity but also the structure of natural systems has remained a daunting challenge. Supramolecular chemists have long endeavored to control the interplay between covalent and noncovalent bond formation, so as to examine and fully comprehend how function is predicated on self-assembly. The ability to reliably control polymer self-assembly is essential to generate "smart" materials and has the potential to tailor polymer properties (i.e., viscosity, electronic properties) through fine-tuning the noncovalent interactions that comprise the polymer architecture. In this context, supramolecular polymers have a distinct advantage over fully covalent systems in that they are dynamically modular, since noncovalent recognition motifs can be engineered to either impart a desired functionality within the overall architecture or provide a designed bias for the self-assembly process. In this Account, we describe engineering principles being developed and pursued by our group that exploit the orthogonal nature of noncovalent interactions, such as hydrogen bonding, metal coordination, and Coulombic interactions, to direct the self-assembly of functionalized macromolecules, resulting in the formation of supramolecular polymers. To begin, we describe our efforts to fabricate a modular poly(norbornene)-based scaffold via ring-opening metathesis polymerization (ROMP), wherein pendant molecular recognition elements based upon nucleobase-mimicking elements (e.g., thymine, diaminotriazine) or SCS-Pd(II) pincer were integrated within covalent monofunctional or symmetrically functionalized polymers. The simple polymer backbones exhibited reliable self-assembly with complementary polymers or small molecules. Within these systems, we applied successful protecting group strategies and template polymerizations to enhance the control afforded by ROMP. Main-chain-functionalized alternating block polymers based upon SCS-Pd(II) pincer-pyridine motifs were achieved through the combined exploitation of bimetallic initiators and supramolecularly functionalized terminators. Our initial design principles led to the successful fabrication of both main-chain- and side-chain-functionalized poly(norbornenes) via ROMP. Utilizing all of these techniques in concert led to engineering orthogonality while achieving complexity through the installation of multiple supramolecular motifs within the side chain, main chain, or both in our polymer systems. The exploitation and modification of design principles based upon functional ROMP initiators and terminators has resulted in the first synthesis of main-chain heterotelechelic polymers that self-assemble into A/B/C supramolecular triblock polymers composed of orthogonal cyanuric acid-Hamilton wedge and SCS-Pd(II) pincer-pyridine motifs. Furthermore, supramolecular A/B/A triblock copolymers were realized through the amalgamation of functionalized monomers, ROMP initiators, and terminators. To date, this ROMP-fabricated system represents the only known method to afford polymer main chains and side chains studded with orthogonal motifs. We end by discussing the impetus to attain functional materials via orthogonal self-assembly. Collectively, our studies suggest that combining covalent and noncovalent bonds in a well-defined and precise manner is an essential design element to achieve complex architectures. The results discussed in this Account illustrate the finesse associated with engineering orthogonal interactions within supramolecular systems and are considered essential steps toward developing complex biomimetic materials with high precision and fidelity.

Tungsten Oxo Alkylidene Complexes as Initiators for the Stereoregular Polymerization of 2,3-Dicarbomethoxynorbornadiene

We have employed 2,3-dicarbomethoxynorbornadiene (DCMNBD) as a monomer to explore new tungsten oxo alkylidene complexes as initiators for stereoregular ROMP (ring-opening metathesis polymerization). The initiators include MAP (monoaryloxide pyrrolide) oxo alkylidene complexes with the general formula W(O)(CHCMe2Ph)(Me2Pyr)(OAr) (Me2Pyr = 2,5-dimethylpyrrolide, OAr = an aryloxide) and W(O)(CHCMe2Ph)(OR)2 (OR = an aryloxide or OC(CF3)3), or PPh2Me or CH3CN adducts thereof. We have found that MAP initiators yield cis,syndiotactic-poly(DCMNBD) as a consequence of stereogenic metal control. In contrast, W(O)(CHCMe2Ph)(OR)2(L) initiators (where L = PPh2Me or acetonitrile) are strongly biased toward formation of cis,isotactic structures, while W(O)(CHCMe2Ph)(OR)2 initiators are strongly biased toward formation of cis,syndiotactic structures. Addition of B(C6F5)3 to W(O)(CHCMe2Ph)(Me2Pyr)(OR) species leads to a dramatic increase in the rate of polymerization and to an increase in the cis,syndiotacticity of the po...

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.

Electronicvs. Steric Hindrance Effects in Amine Ligands to Ru-Based Initiators for ROMP

[RuCl2(PPh3)2(amine)x]-type complexes, with NH2Ph (1; x = 2), NH2Bz (2; x = 2) and NHBuPh (3; x = 1) in the presence of ethyldiazoacetate (EDA), were investigated for ring opening metathesis polymerization (ROMP) of norbornene (NBE), norbornadiene (NBD) and dicyclopentadiene (DCPD). Quantitative yields of polyNBE were obtained at 50 °C for 30 min with 1 and for 5 min with 2, whereas this occurred at 25 °C for 5 min with 3. Polydispersity index (PDI) values ranged from 3.5 to 1.6 (M w = 10 4 -10 5 g mol -1 ). Complex 3 was active for ROMP of NBD and DCPD, as well as for copolymerizations of NBE with either NBD or DCPD. The high σ-donor character of NH2Bz favored the reactivity of the six-coordinated complex 2, contrary to complex 1. The large cone angle of NHBuPh defined the fivecoordination in 3 and the best reactivity for ROMP, in spite of the low σ-donor character as in NH2Ph.

Polymerization of Protecting-Group-Free Peptides via ROMP.

A study was conducted to survey the tolerance of ring-opening metathesis polymerization (ROMP) with respect to amino acid (a.a) identity of pentapeptide-modified norbornene-based monomers. A library of norbornyl-pentapeptides were prepared with the general structure, norbornyl-GX2PLX5, where residue 'X' was changed at each of the two positions (2 or 5) alternately to consist of the natural amino acids F, A, V, R, S, K, N, T, M, Q, H, W, C, Y, E, Q, and D. Each peptide monomer, free of protecting groups, was mixed in turn under a standard set of polymerization conditions with the ROMP initiator (IMesH2)C5H5N)2(Cl)2Ru=CHPh. Two sets of polymerization reactions were performed, one with Monomer:Initiator (M:I) ratio of 20:1, and another with M:I of 200:1. For the nucleophilic amino acids cysteine and lysine, polymerization reactions were quantitatively compared to those of their protected analogues. Furthermore, we describe polymerization of macromonomers containing up to 30 a.a. to test for tolerance of ROMP to peptide molecular weight. These reactions were studied via SEC-MALS and NMR. Finally, with knowledge of sequence scope in hand, we prepared a set of enzyme-substrate containing brush polymers and studied them with respect to their bioactivity.

Olefin metathesis catalyst bearing a chelating phosphine ligand

An improved synthetic procedure for the complex (SPY-5-34)-dichloro-(κ 2(C,P)-diphenyl-(2-benzylidene)-phosphine)-(1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydro-imidazol-2-ylidene)-ruthenium ( 2) was elaborated and the title compound was tested as latent initiator in Ring Opening Metathesis Polymerization (ROMP) and as catalyst for Ring-Closing Metathesis (RCM) at elevated temperatures. While not particularly suited as latent initiator for ROMP, exhibiting a switching temperature of only 42 °C in the polymerization of a typical norbornene derivative, 2 shows an appealing performance in RCM of α,ω-dienes at higher temperatures.

Cis/trans Gradients in living ring-opening metathesis polymerization

The chain microstructure (cis/trans ratio) in ring-opening metathesis polymerization (ROMP) of norbornene and methyltetracyclododecene (MTD) using the Schrock-type initiator Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(OCMe3)2 is shown to be a strong function of monomer concentration, providing a convenient means for tuning the average trans content in the resulting polymers. Moreover, since this is a “living” ROMP initiator, chains formed in batch polymerizations show a continuous gradient of trans content down the chain, with the trans content increasing with conversion. This gradient can be quite substantial; for a typical norbornene polymerization, trans content varies from 30% at one end of the chain to nearly 80% at the other end. The results are explained based on a literature kinetic description for the behavior of this initiator, where cis and trans units are added to the chain by syn and anti rotamers of the active site, respectively. A quantitative mathematical description is developed for the chain microstructure, and associated kinetic parameters are measured for norbornene and MTD at room temperature. The model accurately describes both the variation in average trans content with starting monomer concentration, and the gradients in trans content measured via samples taken at different conversions throughout the polymerization. In contrast, ROMP of MTD using the first-generation Grubbs’ initiator Ru(CHPh)Cl2(PCy3)2 shows no down-chain gradient in trans content.

Inherently reactive polyHIPE material from dicyclopentadiene

A simple formulation of a stable high internal phase emulsion of dicyclopentadiene which is cured by using properly selected ring opening metathesis polymerization initiators yields highly porous monolithic materials with paramount mechanical properties and the possibility of easy functionalisation.

Ru−Alkylidene Metathesis Catalysts Based on 1,3-Dimesityl-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidenes: Synthesis, Structure, and Activity

Novel 1,3-dimesityl-4,5,6,7-tetrahydro-[1,3]-diazepin-2-ylidene-coordinated Ru−alkylidene complexes RuCl2(1,3-dimesityl-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidene)(═CH-2-(2-PrO)C6H4) (2) and Ru(CF3COO)2(1,3-dimesityl-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidene)(═CH-2-(2-PrO)C6H4) (3) were synthesized from the first-generation Grubbs−Hoveyda catalyst, [RuCl2(PCy3)(═CH-2-(2-PrO)C6H4)] (1). The single-crystal X-ray structure of 3 was determined. Compound 2 showed excellent reactivity in ring-opening metathesis polymerization (ROMP) of cis-cycloocta-1,5-diene (COD), yielding polymers with a high trans-content of 80%. Compound 3 is also an active initiator for ROMP; however, a low trans-content of only 14% was found for poly-COD prepared by this initiator. Both 2 and 3 turned out to be good catalysts for cross-metathesis (CM), while both compounds showed only moderate activity in ring-closing metathesis (RCM). Finally, 3 is also a good polymerization catalyst for the regioselective cyclopolymerization of dipropar...

Ring-opening metathesis polymerization for the preparation of norbornene-based weak cation-exchange monolithic capillary columns

Functionalized monolithic columns were prepared via ring-opening metathesis polymerization (ROMP) within silanized fused silica capillaries with an internal diameter of 200 μm by in situ grafting. This procedure is conducted in two steps, the first of which is the formation of the basic monolithic structure by polymerization of norborn-2-ene (NBE) and 1,4,4a,5,8,8a-hexahydro-1,4,5,8- exo, endo-dimethanonaphthalene (DMN-H6) in a porogenic system (toluene and 2-propanol) using RuCl 2(PCy 3) 2(CHPh) as ROMP initiator. In the second step the still active initiator sites located on the surface of the structure-forming microglobules were used as receptor groups for the attachment (“grafting”) of functional groups onto the monolithic backbone by flushing the monolith with 7-oxanorborn-2-ene-5,6-carboxylic anhydride (ONDCA). Functionalization conditions were first defined that did not damage the backbone of low polymer content (20%) monoliths allowing high-throughput chromatographic separations. Variation of the functionalization conditions was then shown to provide a means of controlling the degree of functionalization and resulting ion-exchange capacity. The maximum level of in situ ONDCA grafting was obtained by a 3 h polymerization in toluene at 40 °C. The weak cation-exchange monoliths obtained provided good separation of a standard peptide mixture comprising four synthetic peptides designed specifically for the evaluation of cation-exchange columns. An equivalent separation was also achieved using the lowest capacity column studied, indicative of a high degree of robustness of the functionalization procedure. As well as demonstrably bearing ionic functional groups enabling analyte separation in the cation-exchange mode, the columns exhibited additional hydrophobic characteristics which influenced the separation process. The functionalized monoliths thus represent useful tools for mixed-mode separations.

Photochemical reactions of [W(CO) 4(η 4-nbd)] with hydrosilanes: Generation of new hydrido complexes of tungsten and their reactivity

Photolysis of the norbornadiene (nbd) complex [W(CO) 4(η 4-nbd)] ( 1) creates a coordinatively unsaturated d 6 species which interacts with the Si–H bond of tertiary and secondary silanes (Cl 3SiH, Et 3SiH, Et 2SiH 2, Ph 2SiH 2) to yield hydride complexes of varying stability. In reaction of complex 1 with Cl 3SiH, oxidative addition of the Si–H bond to the tungsten(0) center gives the seven-coordinate tungsten(II) complex [WH(SiCl 3)(CO) 3(η 4-nbd)], which has been fully characterized by NMR spectroscopic methods ( 1H, 13C{ 1H}, 2D 1H– 1H COSY, 2D 13C– 1H HMQC and 29Si{ 1H}). Reaction of 1 with Et 3SiH leads to the hydrosilylation of the η 4-nbd ligand to selectively yield endo-2-triethylsilylnorbornene (nbeSiEt 3). The latter silicon-substituted norbornene gives the unstable pentacarbonyl complex [W(CO) 5(η 2-nbeSiEt 3)], whose conversion leads to the initiation of ring-opening metathesis polymerization (ROMP). Reaction of secondary silanes (Et 2SiH 2 and Ph 2SiH 2) with 1 leads to the hydrosilylation and hydrogenation of nbd and the formation of bis(silyl)norbornane and silylnorbornane as the major products. In reaction of 1 and Et 2SiH 2, the intermediate dihydride complex [WH(μ-H–SiEt 2)(CO) x (η 4-nbd)] was detected by 1H and 13C NMR spectroscopy. As one of the products formed in photochemical reaction of W(CO) 6 with Ph 2SiH 2, the dinuclear complex [{W(μ-η 2-H–SiPh 2)(CO) 4} 2] was identified by NMR spectroscopic methods.

Synthesis of ABA Triblock Copolymers via Ring Opening Metathesis Polymerization Using a Bimetallic Initiator: Influence of a Flexible Spacer in the Side Chain Liquid Crystalline Block

A series of monomers with side chain liquid crystals (SCLCs) were synthesized for ring opening metathesis polymerization (ROMP). The liquid crystals (LCs) used were 4-hydroxybenzoic acid 4-methoxyphenyl ester (MPOB-H), which is known to exhibit a nematic liquid crystalline phase, and biphenyl-4-carboxylic acid 4-(1-butoxycarbonylethoxy)phenyl ester (BPP4-H), which is known to exhibit a smectic phase. The side chains differed in spacer length, spacer type, and the nature of the LC. Monomers were polymerized using a bimetallic ROMP initiator [Mo(NAr)(OCMe3)2CH]2C6H4 (where Ar = 2,6-diisopropyl phenyl); both homopolymers and ABA type triblock copolymers, where the B block is the LC functional monomer, and A is methyltetracyclodocene (MTD) were prepared. The polymers gave unimodal peak distributions with polydispersities <1.22. Incorporation of a polyoxyethylene spacer decreased the glass transition temperature of the polymer block to −25 from +20 °C, the Tg when an alkyl spacer was used. Although no distinct LC phase was observed with the polyoxyethylene spacer when MPOB was used, when BPP4 was attached via a polyoxyethylene spacer, a distinct liquid crystalline transition was observed. Polymers with an alkyl spacer exhibited liquid crystalline behavior and good phase segregation on the basis of differential scanning calorimetry and small-angle X-ray scattering studies.

Fluorescence‐labeled olefin metathesis polymerization initiators

Three ring-opening metathesis polymerization initiators, featuring fluorescence-labeled carbene functionalities, were prepared and characterized. The initiators allowed the preparation of ring-opening-metathesis-derived homopolymers and copolymers featuring fluorescent functionalities as the end groups.

Photochemical reaction of W(CO) 6 with GeCl 4 as a source of germyl and germylene compounds acting as initiators for ring-opening metathesis polymerization of norbornene

Photolysis of W(CO) 6 in a solution of n-heptane containing GeCl 4 leads to the formation of two seven-coordinate compounds with direct W Ge bonds: [(CO) 4W(μ-Cl) 3W(GeCl 3)(CO) 3] ( 1) and [(μ-GeCl 2){W(CO) 5} 2] ( 2). The molecular structures of these two tungsten–germanium compounds have been established by single-crystal X-ray diffraction studies. The germyl compound 1 is a previously synthesized binuclear complex of tungsten(II) with a d 4 electronic configuration, while in the new germylene compound 2 the tungsten atom is formally in the zero oxidation state with a d 6 electronic configuration and a direct W W bond. In an attempt to establish whether compounds 1 and 2 could be used as precatalysts for the ring-opening metathesis polymerization (ROMP) of cyclic olefins, their reactivity towards norbornene has been studied. In chloroform- d 1 solution the ROMP reaction is accompanied by the formation of a new olefin, 2,2′-binorbornylidene (bi-(NBE)), as a result of carbene–carbene coupling. In reaction of norbornene carried out in benzene solution the ROMP reaction is accompanied by the formation of 2-phenylnorbornane (hydroarylation product) and small amounts of bi-(NBE). In general, in the presence of olefin, compound 2 undergoes rearrangement to give an olefin compound of the type [(WCO) 5(η 2-olefin)].

Sequential Electrografting and Ring‐Opening Metathesis Polymerization: a Strategy for the Tailoring of Conductive Surfaces

AbstractSummary: An electrografting technique has been combined with ring‐opening metathesis polymerization (ROMP). Poly(allyl methacrylate) chains have been chemisorbed onto steel and carbon plates under an appropriate cathodic potential in N,N‐dimethylformamide. The allyl moieties have been converted into Ru catalysts active in ROMP of norbornene and its derivatives. Initiation of ROMP from the surface is an efficient strategy to prepare strongly adhering coatings of tunable thickness and hydrophilic/hydrophobic balance, depending on the norbornene derivative polymerized at the surface.The hydrophobicity of the polymer coating may be controlled by hydrolysis of the polynorbornene derivative.magnified imageThe hydrophobicity of the polymer coating may be controlled by hydrolysis of the polynorbornene derivative.

Synthesis of Narrow-Distribution “Perfect” Polyethylene and Its Block Copolymers by Polymerization of Cyclopentene

Polycyclopentene with controllable molecular weight and polydispersity below 1.1 was obtained by ring-opening metathesis polymerization (ROMP) of cyclopentene at room temperature using a commercial Mo-based ROMP initiator in the presence of trimethylphosphine. Polydispersities were kept low by limiting the degree of cyclopentene conversion. These narrow-distribution polycyclopentenes were catalytically hydrogenated to narrow-distribution linear polyethylenes, providing a facile route to model polyethylenes free from both short- and long-chain branching. The “living” nature of ROMP also permits the synthesis of well-defined diblock copolymers containing polycyclopentene, including poly(ethylidenenorbornene)−polycyclopentene diblocks. The hydrogenated derivatives of these diblocks represent a new type of crystalline−amorphous diblock, possessing much higher levels of crystallinity than when block copolymers containing anionically polymerized high-1,4-polybutadiene are hydrogenated.

Ligand Effects in Novel Ruthenium-Based ROMP Catalysts Bearing Bidentate Phosphines

Complexes of general formula [(Cy2P(CH2)nPCy2)Ru(η3-C4H7)2] (n = 1−3) are halide-free initiators for ring-opening metathesis polymerization (ROMP) of norbornene. The chain length of the chelating phosphine exhibits an effect on the polymer yield and the stereochemistry at the CC double bond. Analysis of the resulting polymer by GPC and electron microscopy indicates an initiation efficiency of approximately 10%. A mechanism for the formation of the propagating species is proposed that involves merging of the two allyl moieties and cycloreversion of the resulting ruthenacyclobutane to give a carbene intermediate containing a cis-PRuP chelate ring.