Ring-opening Metathesis Copolymerization Research Articles

Bridging of poly(acetylene)s and PEG-modified poly(olefin)s through ring-opening metathesis copolymerization (ROMCP)

Amphiphilic copolymers of highly conjugated poly(acetylene)s and PEG–PDI-incorporating poly(olefin)s have been synthesized and analyzed to study their amphiphilic properties, H-type aggregation processes and self-assembling behavior.

Living Alternating Ring-Opening Metathesis Copolymerization of 2,3-Dihydrofuran to Provide Completely Degradable Polymers.

2,3-Dihydrofuran (DHF) has recently been gaining significant attention as a comonomer in metathesis polymerization, thanks to its ability to provide the resultant polymer backbones with stimuli-responsive degradability. In this report, we present living alternating copolymerization of DHF with less reactive endo-tricyclo[4.2.2.02,5 ]deca-3,9-dienes (TDs) and endo-oxonorbornenes (oxoNBs). By carefully controlling the reactivity of both the Ru initiators and the monomers, we have achieved outstanding A, B-alternation (up to 98 %) under near stoichiometric DHF loading conditions. Notably, we have also found that the use of a more sterically hindered Ru initiator helps to attain polymer backbones with higher DHF incorporation and superior A, B-alternation. While preserving the living characteristics of DHF copolymerization, as evidenced by controlled molecular weights (up to 73.9 kDa), narrow dispersities (down to 1.05), and block copolymer formation, our DHF copolymers could be broken down to a single repeat unit level under acidic conditions. 1 H NMR analysis of the model copolymer revealed that after 24 hours of degradation, up to 80 % of the initial polymer was transformed into a single small molecule product, and after purification, up to 66 % of the degradation product was retrieved. This study provides a versatile approach to improve the alternation and degradability of DHF copolymers.

Effect of Chain Structure on the Various Properties of the Copolymers of Fluorinated Norbornenes with Cyclooctene.

Fluorinated polymers are attractive due to their special thermal, surface, gas separation, and other properties. In this study, new diblock, multiblock, and random copolymers of cyclooctene with two fluorinated norbornenes, 5-perfluorobutyl-2-norbornene and N-pentafluorophenyl-exo-endo-norbornene-5,6-dicarboximide, are synthesized by ring-opening metathesis copolymerization and macromolecular cross-metathesis in the presence of the first- to third-generation Grubbs' Ru-catalysts. Their thermal, surface, bulk, and solution characteristics are investigated and compared using differential scanning calorimetry, water contact angle measurements, gas permeation, and light scattering, respectively. It is demonstrated that they are correlated with the chain structure of the copolymers. The properties of multiblock copolymers are generally closer to those of diblock copolymers than of random ones, which can be explained by the presence of long blocks capable of self-organization. In particular, diblock and multiblock fluorine-imide-containing copolymers show a tendency to form micelles in chloroform solutions well below the overlap concentration. The results obtained may be of interest to a wide range of researchers involved in the design of functional copolymers.

Alternating Ring-Opening Metathesis Polymerization Promoted by Ruthenium Catalysts Bearing Unsymmetrical NHC Ligands

In this paper, Grubbs- and Hoveyda–Grubbs-type olefin metathesis catalysts featuring N-cyclopentyl/N’-mesityl backbone-substituted N-heterocyclic carbene (NHC) ligands were synthesized. Their propensity to promote the alternating ring-opening metathesis copolymerization (ROMP) of norbornene (NBE) with cyclooctene (COE) or cyclopentene (CPE) was evaluated and compared to that shown by analogous N-cyclohexyl complexes. High degrees of chemoselectivity were achieved in both copolymerizations. The presence of the N-cyclopentyl substituent allowed for the achievement of up to 98% and 97% of alternating diads for NBE-COE and NBE-CPE copolymers, respectively, at low comonomer ratios. Density functional theory (DFT) studies showed that both the sterical and electronic effects of NHC ligands influence catalyst selectivity.

Catalytic Living Ring‐Opening Metathesis Polymerization Using Vinyl Ethers as Effective Chain‐Transfer Agents

AbstractA catalytic living ring‐opening metathesis copolymerization (ROMP) method is described that relies on a degenerative, reversible and regioselective exchange of propagating Fischer‐carbenes. All characteristics of a living polymerization such as narrow dispersity, excellent molar mass control and the ability to form block copolymers are achieved by this method. The method allows the use of up to 200 times less ruthenium complex than traditional living ROMP. We demonstrate the synthesis of ROMP‐ROMP diblock copolymers, ATRP from a ROMP macro‐initiator and living ROMP from a PEG‐based macro chain transfer agent. The cost‐effective, sustainable and environmentally friendly synthesis of degradable polymers and block copolymers enabled by this strategy will find various applications in biomedicine, materials science, and technology.

Catalytic Living Ring-Opening Metathesis Polymerization Using Vinyl Ethers as Effective Chain-Transfer Agents.

A catalytic living ring-opening metathesis copolymerization (ROMP) method is described that relies on a degenerative, reversible and regioselective exchange of propagating Fischer-carbenes. All characteristics of a living polymerization such as narrow dispersity, excellent molar mass control and the ability to form block copolymers are achieved by this method. The method allows the use of up to 200 times less ruthenium complex than traditional living ROMP. We demonstrate the synthesis of ROMP-ROMP diblock copolymers, ATRP from a ROMP macro-initiator and living ROMP from a PEG-based macro chain transfer agent. The cost-effective, sustainable and environmentally friendly synthesis of degradable polymers and block copolymers enabled by this strategy will find various applications in biomedicine, materials science, and technology.

Bulk ring-opening metathesis copolymerization of dicyclopentadiene and 5-ethylidene-2-norbornene: mixing rules, polymerization behaviors and properties

Bulk ring-opening metathesis copolymerization of dicyclopentadiene and 5-ethylidene-2-norbornene: mixing rules, polymerization behaviors and properties

Rapid Access to Diverse Multicomponent Hierarchical Nanostructures from Mixed-Graft Block Copolymers.

Multicomponent nanostructured materials assembled from molecular building blocks received wide attention due to their precisely integrated multifunctionalities. However, discovery of these materials with desirable composition and morphology was limited by their low synthetic scalability and narrow structural tuning window with given building blocks. Here, we report a scalable and diversity-oriented synthetic approach to hierarchically structured nanomaterials based on a few readily accessible building blocks. Mixed-graft block copolymers containing sequence-defined side chains were prepared through ring-opening metathesis copolymerization of three or four types of macromonomers. Intramolecularly defined interfaces promoted the formation of ordered hierarchical structures with lattice sizes tunable across multiple length scales. The same set of macromonomers were arranged and combined in different ways, providing access to diverse morphologies in the resultant structures.

Catalytic Syntheses of Degradable Polymers via Ring-Opening Metathesis Copolymerization Using Vinyl Ethers as Chain Transfer Agents

Catalytic Syntheses of Degradable Polymers via Ring-Opening Metathesis Copolymerization Using Vinyl Ethers as Chain Transfer Agents

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.

A versatile approach for the synthesis of degradable polymers via controlled ring-opening metathesis copolymerization

Norbornene derivatives (NBEs) are common monomers for living ring-opening metathesis polymerization and yield polymers with low dispersities and diverse functionalities. However, the all-carbon backbone of poly-NBEs is non-degradable. Here we report a method to synthesize degradable polymers by copolymerizing 2,3-dihydrofuran with NBEs. 2,3-Dihydrofuran rapidly reacts with Grubbs catalyst to form a thermodynamically stable Ru Fischer carbene-the only detectable active Ru species during copolymerization-and the addition of NBEs becomes rate determining. This reactivity attenuates the NBE homoaddition and allows uniform incorporation of acid-degradable enol ether linkages throughout the copolymers, which enables complete polymer degradation while maintaining the favourable characteristics of living ring-opening metathesis polymerization. Copolymerization of 2,3-dihydrofuran with NBEs gives low dispersity polymers with tunable solubility, glass transition temperature and mechanical properties. These polymers can be fully degraded into small molecule or oligomeric species under mildly acidic conditions. This method can be readily adapted to traditional ring-opening metathesis polymerization of widely used NBEs to synthesize easily degradable polymers with tunable properties for various applications and for environmental sustainability.

Real time monitoring by time-domain NMR of ring opening metathesis copolymerization of norbornene-based red palm olein monomer with norbornene

Changes in molecular mobility throughout the metathesis copolymerization of a norbornene functionalized with a palm olein monomer and a pure norbornene were monitored in situ by time-domain 1H NMR, using a ruthenium catalyst. Reaction progress to produce branched palm oil-based copolymers was studied as a function of the amounts of monomers and catalyst. Transverse relaxation rates were determined from CPMG experiments and the results were in accordance with the reactivity ratios, which indicated production of gradient copolymers. Properties of the resulting material observed through TD-NMR measurements of the isolated copolymers corroborated the type of the used monomers. TD-NMR demonstrated to be a useful tool for learning copolymerization reactions, particularly in ROMP, for the first time.

Alternating Ring-Opening Metathesis Polymerization Provides Easy Access to Functional and Fully Degradable Polymers.

Polymers with hydrolyzable groups in their backbones have numerous potential applications in biomedicine, lithography, energy storage and electronics. In this study, acetal and ester functionalities were incorporated into the backbones of copolymers by means of alternating ring-opening metathesis polymerization catalyzed by third-generation Grubbs ruthenium catalyst. Specifically, combining large-ring (7-10 atoms) cyclic acetal or lactone monomers with bicyclo[4.2.0]oct-1(8)-ene-8-carboxamide monomers provided perfectly alternating copolymers with acetal or ester functionality in the backbones and low to moderate molecular weight distribution (Đ M = 1.2-1.6). Copolymers containing ester and acetal backbones hydrolyzed to significant extent under basic condition (pH 13) and acidic conditions (pH ≤ 5) respectively to yield the expected by-products within 30 hours at moderate temperature. Unlike the copolymer with all-carbon backbone, copolymers with heteroatom-containing backbone exhibited viscoelastic behavior with crossover frequency which decreases as the size of the R group on the acetal increases. In contrast, the glass transition temperature (T g) decreases as the size of the R group decreases. The rate of hydrolysis of the acetal copolymers was also dependent on the R group. Thus, ruthenium-catalyzed alternating ring-opening metathesis copolymerization provides heterofunctional copolymers whose degradation rates, glass transition temperatures, and viscoelastic moduli can be controlled.

Macromolecular Brushes Based on Poly(L-Lactide) and Poly(ε-Caprolactone) Single and Double Macromonomers via ROMP. Synthesis, Characterization and Thermal Properties.

Single and double poly(L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) macromonomers having a norbornenyl polymerizable group were prepared by conventional Ring Opening Polymerization (ROP). These macromonomers were further subjected to ring opening metathesis polymerization (ROMP) reactions in order to produce double polymer brushes consisting of PLLA or PCL side chains on a polynorbornene (PNBE) backbone. Statistical or block ring opening metathesis copolymerization of the PLLA and PCL macromonomers afforded the corresponding random and block double brushes. Sequential ROMP of the single PLLA, PCL and PLLA macromonomers resulted in the synthesis of the corresponding triblock copolymer brush. The molecular characteristics of the macromolecular brushes were obtained by 1H-NMR spectroscopy and Size Exclusion Chromatography. The thermal properties of the samples were studied by thermogravimetric analysis, TGA, Differential Thermogravimetry, DTG and Differential Scanning Calorimetry, DSC.

Frontal Ring-Opening Metathesis Copolymerization: Deviation of Front Velocity from Mixing Rules.

Frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) shows promise for rapid, energy-efficient manufacturing of high-performance polymers and composites. Copolymerization in FROMP allows for systematic modification of materials properties while retaining the benefits of the DCPD system such as low cost of the monomer and excellent mechanical properties of the resulting polymer. While the copolymerization reactivity and copolymer properties generally exhibit monotonic dependence on monomer composition as predicted by simple, empirical mixing rules, we discovered that the frontal copolymerization behavior of DCPD with a dinorbornenyl (di-NBE) cross-linker deviates significantly from that expected relationship. As the comonomer content increases, the FROMP reaction shows a nonmonotonic increase in front velocity with intermediate compositions 40% faster than either pure component. We then studied the behavior of a series of comonomers, analyzed several factors (such as thermodynamic and kinetic properties) that might influence front velocity, and found that the nonmonotonic trend mainly results from the cross-linked structure. This copolymerization system provides a promising strategy to tune materials properties (such as glass transition temperature) and simultaneously improve the efficiency in FROMP-based materials manufacturing.

Long-Chain Polyorthoesters as Degradable Polyethylene Mimics.

The persistence of commodity polymers makes the research for degradable alternatives with similar properties necessary. Degradable polyethylene mimics containing orthoester groups were synthesized by olefin metathesis polymerization for the first time. Ring-opening metathesis copolymerization (ROMP) of 1,5-cyclooctadiene with four different cyclic orthoester monomers gave linear copolymers with molecular weights up to 38000 g mol–1. Hydrogenation of such copolymers produced semicrystalline polyethylene-like materials, which were only soluble in hot organic solvents. The crystallinity and melting points of the materials were controlled by the orthoester content of the copolymers. The polymers crystallized similar to polyethylene, but the relatively bulky orthoester groups were expelled from the crystal lattice. The lamellar thickness of the crystals was dependent on the amount of the orthoester groups. In addition, the orthoester substituents influenced the hydrolysis rate of the polymers in solution. Additionally, we were able to prove that non-hydrogenated copolymers with a high orthoester content were biodegraded by microorganisms from activated sludge from a local sewage plant. In general, all copolymers hydrolyzed under ambient conditions over a period of several months. This study represents the first report of hydrolysis-labile and potentially biodegradable PE mimics based on orthoester linkages. These materials may find use in applications that require the relatively rapid release of cargo, e.g., in biomedicine or nanomaterials.

Ultra-Fast Synthesis of Multivalent Radical Nanoparticles by Ring-Opening Metathesis Polymerization-Induced Self-Assembly.

We report the straightforward, time-efficient synthesis of radical core-shell nanoparticles (NPs) by polymerization-induced self-assembly. A nitroxide-containing hydrophilic macromolecular precursor was prepared by ring-opening metathesis copolymerization of norbornenyl derivatives of TEMPO and oligoethylene glycol and was chain-extended in situ with norbornene in ethanolic solution, leading to simultaneous amphiphilic block copolymer formation and self-assembly. Without any intermediate purification from the monomers to the block copolymers, radical NPs with tunable diameters ranging from 10 to 110 nm are obtained within minutes at room temperature. The high activity of the radical NPs as chemoselective and homogeneous, yet readily recyclable catalysts is demonstrated through oxidation of a variety of alcohols and recovery by simple centrifugation. Furthermore, the NPs show biocompatibility and antioxidant activity in vitro.

Synthesis of Polypeptoid-Polycaprolactone-Polytetrahydrofuran Heterograft Molecular Polymer Brushes via a Combination of Janus Polymerization and ROMP.

Janus polymerization is a novel and efficient way to synthesize diblock and multiblock copolymers in one step by using Lu(OTf)3 and propylene epoxide as a catalytic system. By modifying the epoxide initiator, which is located at the block junction with various functional groups, the possibility for future topological design is provided. Herein, 2-bicyclo[2.2.1]hept-5-en-2-yl oxirane (NB-EO) is used as an alternative for propylene epoxide to synthesize a poly(THF-co-CL)-b-PCL diblock copolymer featuring a norbornene group at this position. This also results in multiblock [poly(THF-co-CL)-b-PCL]m copolymers carrying multiple norbornene moieties through Janus polymerization. Subsequent ring-opening metathesis copolymerization (ROMP) of the resulting poly(THF-co-CL)-b-PCL macromonomers with norbornenyl-terminated polysarcosine (PSar-NB) allows the facile preparation of heterograft molecular polymer brushes (MPBs). The MPBs feature three heterografts of PCL, P(CL-co-THF) and PSar, potentially equipping these structures with biocompatibility, biodegradability, semi-crystallinity, and amphiphilicity. A phase separation is observed after annealing in both TEM and AFM analysis. Due to their amphiphilic nature, the MPBs also undergo self-assembly into micelles in aqueous solution. Such materials combining polypeptoids, polyesters, and polyethers segments are expected to attract wide attention in drug delivery applications.

Syntheses and properties of ABA, CBA, and CBC triblock copolymers based thermoplastic elastomers with glassy (A), elastomeric (B), and crystalline (C) blocks

In this contribution, we describe the syntheses, characterization, and properties of ABA, CBA and CBC triblock copolymers with glassy (A), elastomeric (B), and crystalline (C) blocks. These three hard-soft-hard triblock copolymers were prepared via living ring-opening metathesis copolymerization by use of Grubbs third generation catalyst through one-pot sequential monomer addition and subsequent hydrogenation. These hard-soft-hard triblock copolymers based thermoplastic elastomers have been analyzed by proton NMR, differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), IR, and transmission electron microscopy (TEM). The mechanical properties of these triblock copolymers were also measured by monotonic and step cyclic tensile test. Compared with the ABA triblock copolymer, the CBC triblock copolymer containing highly crystalline hard end-blocks shows enhanced tensile strength and the best elastic recovery of 90.8%. The hybrid CBA triblock copolymer displays much improved elongation, which is almost twice as long as the other two TPEs, and excellent elastic recovery of 87.0%.

A Degradable and Antimicrobial Surface-attached Polymer Hydrogela.

Surface-attached, degradable polymer hydrogels with potential antimicrobial activity are reported. They were obtained by ring-opening metathesis copolymerization (ROMP) of a monomer with potential bioactivity and a monomer that carries a benzophenone cross-linker and a hydrolyzable group. The hydrolyzable group was either an ester or an anhydride group. The copolymers thus obtained were spin-coated onto silicon wafers and UV-irradiated to induce C,H cross-linking of the benzophenone groups and obtain the target polymer networks. Immersion of these networks into aqueous media triggered network degradation. The degradation speed depended on the nature of the intended break points (ester or anhydride groups), the number of cross-links per polymer chain, and the surrounding medium. By releasing bioactive polymer fragments to the medium ("leaching") and by regenerating the hydrogel surface during the degradation process, the hydrogels potentially have two ways to prevent biofilm formation on their surface.