Ring-opening Metathesis Polymerization Polymers Research Articles

PhotoROMP: The Future Is Bright.

Since the earliest investigations of olefin metathesis catalysis, light has been the choice for controlling the catalyst activity on demand. From the perspective of energy efficiency, temporal and spatial control, and selectivity, photochemistry is not only an attractive alternative to traditional thermal manufacturing techniques but also arguably a superior manifold for advanced applications like additive manufacturing (AM). In the last three decades, pioneering work in the field of ring-opening metathesis polymerization (ROMP) has broadened the scope of material properties achievable through AM, particularly using light as both an activating and deactivating stimulus. In this Perspective, we explore trends in photocontrolled ROMP systems with an emphasis on approaches to photoinduced activation and deactivation of metathesis catalysts. Recent work has yielded a myriad of commercial and synthetically accessible photosensitive catalyst systems, although comparatively little attention has been paid to achieving precise control over polymer morphology using light. Metal-free, photophysical, and living ROMP systems have also been relatively underexplored. To take fuller advantage of both the thermomechanical properties of ROMP polymers and the operational simplicity of photocontrol, clear directions for the field are to improve the reversibility of activation and deactivation strategies as well as to further develop photocontrolled approaches to tuning cross-link density and polymer tacticity.

Simultaneous Spin Coating and Ring-Opening Metathesis Polymerization for the Rapid Synthesis of Polymer Films.

We report a highly controlled technique for the synthesis of polymer films atop a substrate by combining spin coating with ring-opening metathesis polymerization (ROMP), herein termed spin coating ROMP (scROMP). The scROMP approach combines polymer synthesis and deposition into one process, fabricating films of up to 36 cm2 in under 3 min with orders-of-magnitude reduction in solvent usage. This method can convert numerous norbornene-type molecules into homopolymers and random copolymers as uniform films on both porous and nonporous substrates. Film thickness can be varied from a few hundred nanometers to a few tens of micrometers based on spin speed and monomer concentration. The resulting polymers possess high MW (>100 kDa) and low polydispersity (PDI) (<1.2) values that are similar to ROMP polymers made in solution. We also devise a model to investigate the balance between convective monomer spin-off and polymer growth from the surface, which allows the determination of critical kinetic parameters for scROMP. Finally, translation of scROMP to porous supports enables the synthesis of thin film composite membranes that demonstrate the ability to dehydrate ethanol by pervaporation.

Synthesis of dendronized PAMAM grafted ROMP polymers

Oxanorbornene cored 0.5, 1.5 and 2.5 generation ester terminated PAMAM dendronized monomers with 2 and 6 carbon-containing alkyl spacer in the middle of oxanorbornene core and dendronized branching were synthesized. Monomers were polymerized through the ring-opening metathesis polymerization (ROMP) technique by using 2nd and 3rd generation Grubbs catalysts to get dendronized ROMP polymers. It was found that Grubbs 3rd generation catalyst works well for 0.5 generation dendronized ROMP polymer whereas Grubbs 2nd generation catalyst works for the higher generation. We also found the linker effect during polymerization as six-carbon linker monomers polymerize with high yield along with higher generation. Finally, dendronized ROMP-based PAMAM encapsulated zero valent Cu nanoparticle was synthesized by using a reducing agent, NaBH4. The catalytic activity of this nanoparticle was further investigated from the reduction of 4-nitrophenol to 4-aminophenol.

Practical Route for Catalytic Ring-Opening Metathesis Polymerization.

Norbornene derivatives are typical monomers for ring-opening metathesis polymerization (ROMP) for synthesizing highly functional polymers. However, the lack of catalytic methods, that is, the lack of readily available chain transfer agents (CTAs) for these monomers has been a significant cost limitation when large-scale syntheses are required. Here, we report commercially available styrene and its derivatives as efficient regioselective CTAs for the catalytic synthesis of metathesis polymers requiring up to 1000 times less ruthenium than in classical ROMP experiments. The molecular weight of the synthesized polymers was controlled by the monomer-to-CTA ratio. Low molecular weight ROMP polymers known for their antimicrobial properties were also synthesized on a gram scale in this report. Polymers were characterized by SEC, 1H NMR spectroscopy, and isotopically resolved MALDI-TOF MS. This approach describes a greener, more cost-effective, and eco-friendly methodology for the preparation of metathesis-based materials on the multigram scale.

Side-Chain Length and Dispersity in ROMP Polymers with Pore-Generating Side Chains for Gas Separations.

Bottlebrush polymers with flexible backbones and rigid side chains have shown ultrahigh CO2 permeability and plasticization resistance for membrane-based gas separations. To date, this class of polymers has only been studied with polydisperse side chains. Herein, we report gas transport properties of a methoxy (OMe) functionalized polymer synthesized via ring-opening metathesis polymerization (ROMP) with uniform side-chain lengths ranging from n = 2 to 5 repeat units to elucidate the role of both side-chain length and dispersity on gas transport properties and plasticization resistance. As side-chain length increased, both Brunauer–Emmett–Teller (BET) surface area and gas permeability increased with minimal losses in gas selectivity. Increased plasticization resistance was also observed with increasing side-chain length, which can be attributed to increased interchain rigidity from longer side chains. Controlling the side-chain length provides an effective strategy to rationally control and optimize the performance of ROMP polymers for CO2-based gas separations.

Star-Shaped ROMP Polymers Coated with Oligothiophenes That Exhibit Unique Emission.

A series of oligo(thiophene)-modified “soluble” star-shaped ring-opening metathesis polymerization (ROMP) polymers were prepared by sequential living ROMP of norbornene and a cross-linking agent using a molybdenum-alkylidene catalyst, followed by Wittig-type coupling for termination with oligo(thiophene) carboxaldehydes. The resultant star-shaped ROMP polymers displayed unique emission properties affected by the core size and arm repeat units as well as the kind of oligothiophene coated. The effects of the thiophene groups on photophysical properties of star-shaped/linear polymers were studied via time-resolved fluorescence spectroscopy. Fluorescence lifetimes were determined in THF as 400, 640, 730, and 820 ps for Star 3TPh, Linear 3TPh, Star 4T, and Linear 4T, respectively. A significant enhancement of the nonradiative rate constants knr in the star-shaped polymers results in relatively lower fluorescence quantum yields and shorter fluorescence lifetimes compared to the corresponding linear polymers.

Turnaround in use of enol ether opens the door to degradable plastics

While ring-opening metathesis polymerization (ROMP) is a robust method to construct polymers, monomer systems for degradable ROMP polymers are limited. Existing systems suffer from lengthy synthesis and/or uncontrolled polymerization. Xia and coworkers demonstrated the synthesis of degradable ROMP copolymers from the commercially available monomers in a controlled manner. While ring-opening metathesis polymerization (ROMP) is a robust method to construct polymers, monomer systems for degradable ROMP polymers are limited. Existing systems suffer from lengthy synthesis and/or uncontrolled polymerization. Xia and coworkers demonstrated the synthesis of degradable ROMP copolymers from the commercially available monomers in a controlled manner.

Chain transfer agents for the catalytic ring opening metathesis polymerization of norbornenes.

Here, we present a detailed study of the metathesis activity of conjugated 1,3 diene derivatives in ring opening metathesis polymerization (ROMP) using Grubbs' 3rd generation catalyst (G3). A comprehensive screening of those derivatives revealed that monosubstituted 1,3 dienes show similar reactivities towards G3-alkylidenes as norbornene derivatives. Therefore, they represent perfect candidates for chain transfer agents in a kinetically controlled catalytic ROMP. This unprecedented reactivity allowed us to catalytically synthesize mono-end-functional poly(norborneneimide)s on the gram scale. Much more complex architectures such as star-shaped polymers could also be synthesized catalytically for the very first time via ROMP. This inexpensive and greener route to produce telechelic ROMP polymers was further utilized to synthesize ROMP block copolymers using bifunctional ROMP and ATRP/NCL initiators. Finally, the regioselective reaction of G3 with 1,3 diene derivatives was also exploited in the synthesis of a ROMP-PEG diblock copolymer initiated from a PEG macroinitiator.

Polymerization of Cyclopropenes: Taming the Strain for the Synthesis of Controlled and Sequence-Regulated Polymers.

Cyclopropenes (CPEs) are highly strained cyclic olefins, yet there are surprisingly limited examples leveraging their high strain energy for polymerization. In the past, attempts had been made to polymerize CPEs via cationic and insertion polymerization, but side reactions often gave uncontrolled polymers with mixed backbone structures. Ring-opening metathesis polymerization (ROMP) represents an ideal strategy for polymerizing CPEs to access new types of polymers. The proximity of substituents to the olefin in the small framework of CPEs offers a modular handle to tune the kinetic barrier to propagation by the modulation of the substituents. While the first few studies focused on the homopolymerization of simple alkyl or phenyl disubstituted CPEs, we recently explored the metathesis of a wide range of CPEs with different substituents using Grubbs catalysts and discovered surprising and diverse reactivities that are contingent on the positions, sterics, and electronics of substituents. The observed reactivities ranged from living homopolymerization to catalyst deactivation to single addition to the catalyst without homopropagation. In particular, the exclusively single addition reactivity found in two families of CPEs, with either bis(methanol ester) or phenyl and methanol ester substituents at the allylic position, is unusual for any monomer and perhaps counterintuitive for highly strained cycles. These single-addition CPEs could, however, be copolymerized with low-strain cyclic olefins to generate perfectly alternating copolymers with controlled molecular weights and low dispersity and to introduce degradable backbone linkages. A single equivalent (relative to the active chain end) of such CPEs could also be added to the active chain end of living ROMP polymers to install functional terminal groups or during living ROMP to place single units of functional moieties or side chains at any desired chain locations in narrow-disperse homopolymers and block copolymers. This account summarizes the polymerization of CPEs with a focus on our journey to uncover the rich and unique metathesis reactivities of CPEs and their utility in synthesizing well-controlled and sequence-regulated polymers. It provides the first collective structure-metathesis reactivity relationships for CPEs in the context of polymer chemistry and an understanding of the interactions between the catalyst and the substituents of appended ring-opened CPEs. It may become clear from this Account that the exploration of strained cycles in polymer chemistry can be quite fruitful in discovering new chemistry and accessing new types of polymer materials.

Poly(norbornenyl azlactone) as a versatile platform for sequential double click postpolymerization modification

Ring-opening metathesis polymerization (ROMP) of a heterofunctional azlactone-based monomer, namely norbornenyl azlactone (NBAzl), is reported for the first time using third generation ruthenium-based catalyst (G3′). It is demonstrated that ROMP of the mixture of stereoisomers of NBAzl obtained by Diels-Alder reaction between 2-vinyl-4,4-dimethyl-5-oxazolone (vinyl azlactone, VDM) and cyclopentadiene leads to well-defined polymers (Mn, SEC¯ up to 52 500 g mol−1, Ð < 1.37). The resulting polymers easily undergo click postpolymerization modification by aminolysis of the azlactone groups using amine nucleophiles. By using azido oligoethylene glycol amine, ROMP polymers having azido side-chains capable of alkyne azide click modification are prepared, that are not attainable by direct ROMP of azido-functionalized monomers. The successful clicking to the so-obtained azido-functional ROMP polymer was demonstrated by copper-catalyzed alkyne − azide cycloaddition (CuAAC) with alkyne-functionalized fluorescein. The reported versatile methodology produces with complete atom economy a platform for new functional polymer libraries, including polymer materials with potential medical and biological applications.

ROMP polymer supported manganese porphyrins: Influence of C[dbnd]C bonds along polymer chains on catalytic behavior in oxidation of low concentration Fe2+

One unsaturated polymer support was prepared through ring opening metathesis polymerization (ROMP) of norbornene-2,3-dip-toluene sulfonate initiated by Grubbs 2nd initiator and manganese porphyrins were immobilized on polymer through transesterification reaction. To investigate the effect of CC bonds along polymer chains on the catalytic behavior, the obtained polymer supported catalyst (P-PPIXMnCl) was applied in oxidation of low concentration Fe2+ to mimic catalytic behavior of Ceruloplasmin. In the presence of P-PPIXMnCl, the conversion of Fe2+ reaches to 91.92% and 96.46% at 10 °C and 37.5 °C (body temperature), respectively. Compared to manganese porphyrins, P-PPIXMnCl can dramatically increase oxidation rate of Fe2+ and the catalytic kinetic shows that the oxidation reaction changes from second-order to third-order. Upon hydrogenation of ROMP polymer, the oxidation reaction still conforms to the second-order kinetics. Density functional theory (DFT) calculation shows that the CC bonds along polymer chains play an important role in the coordination with Fe2+ in the catalytic microenvironment. The real time morphology of supported catalysts in aqueous environment characterized by Cryo-TEM indicates that hydrogenation can shrink the morphology of polymer-water skeleton. The catalyst could be recycled six times without any significant loss in activity. The liner heterogeneous catalyst is expected to be used as drugs for treating excessive iron accumulation in the human body.

Catalytic living ring-opening metathesis polymerization with Grubbs' second- and third-generation catalysts.

In a conventional living ring-opening metathesis polymerization (ROMP), an equal number of ruthenium complexes to the number of polymer chains synthesized are required. This can lead to high loadings of ruthenium complexes when aiming for shorter polymers. Here, a reversible chain-transfer agent was used to produce living ROMP polymers from norbornene derivatives using catalytic amounts of Grubbs' ruthenium complexes. The polymers obtained by this method showed all of the characteristics of a living polymerization (that is, good molecular weight control, narrow molecular weight dispersities and the ability to form block copolymers). Monomers carrying functional moieties such as ferrocene, coumarin or a triisopropylsilyl-protected primary alcohol could also be catalytically polymerized in a living fashion. The method presented follows a degenerative chain-transfer process and is more economical and environmentally friendly compared with previous living ROMP procedures as it utilizes only catalytic amounts of costly and toxic ruthenium complexes.

Synthesis and characterization of a ROMP-based polycationic antimicrobial hydrogel

This study has investigated the antimicrobial potential of ring opening metathesis polymerization (ROMP)-based hydrogels. Initially, double charge containing cationic (DABCO)-ROMP polymers were synthesized and characterized. Subsequently, DABCO-ROMP polymer was added into a hydrogel formulation comprised of acrylamide (AAm), N,N'-methylenebis(acrylamide) (BAAm) and/or poly(ethylene glycol) diacrylate (PEG diacrylate, Mn = 700 g/mol) in different quantities to investigate the antimicrobial efficiency of the hydrogel formulations. N,N,N′,N′-tetramethyl ethylene diamine (TEMED) is used with ammonium persulfate (APS) to catalyze polymerization in water. The structures of the resulting hydrogels were characterized using infrared spectroscopy (IR). The cross-linking properties and surface morphologies were investigated via the swelling behavior and scanning electron spectroscopy (SEM). Fluorescein (Na salt) staining measurements were also used to analyze the positive charge density of the hydrogels. The antimicrobial hydrogels showed excellent antimicrobial efficacy against Escherichia coli (E. coli, ATCC 25922), Staphylococcus aureus (S. aureus, ATCC 29213) and Candida albicans (C. albicans, ATCC 90028). It was observed that the cationic ROMP polymer in the hydrogel formulation played a crucial role in the biocidal activity. Furthermore, cytotoxicity studies on human umbilical vein endothelial cells (HUVEC) and tetrazolium salt assay (MTS) cell lines were also performed on the hydrogels and the most potent copolymer revealed no cytotoxicity. Therefore, the ROMP-based hydrogels show good biocidal properties with potential applications in various biomedical fields.

Assessing structure/property relationships and synthetic protocols in the fabrication of poly(oxanorbornene imide) single-chain nanoparticles

We present the synthesis of poly(oxanorbornene imide) single-chain nanoparticles (SCNP) by intrachain radical polymerization of pendant methacryloyl units. Well-defined poly(oxanorbornene imide)s were first prepared via ring-opening metathesis polymerization (ROMP) of methacryloyl-containing monomers. Handling and polymerizing these monomers requires some special care to prevent undesired premature reaction of the methacryloyl groups. Addition of AIBN to dilute solution of the ROMP polymers triggers intrachain radical polymerization of pendant methacryloyl groups, folding the linear polymers into SCNP. Characterization by NMR spectroscopy and SEC confirmed SCNP formation and revealed structure/property relationships related to methacryloyl pendent length and percent incorporation.

Synthesis of Soluble Star-Shaped Polymers via In and Out Approach by Ring-Opening Metathesis Polymerization (ROMP) of Norbornene: Factors Affecting the Synthesis

The methods for one-pot synthesis of ‘soluble’ star-shaped polymers by sequential living ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and cross-linking (CL) reagent using Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 have been explored. The method (called the “in and out” or core-first approach) basically consists of (i) the living ROMP of NBE (formation of arm), (ii) reaction with CL (formation of core), (iii) additional living ROMP of NBE (propagating arms from the core, formation of star), (iv) end-modification via Wittig-type cleavage of metal–carbon double bonds containing polymer chain with aldehyde. Two different approaches in the core formation step (reaction with CL mixed with/without NBE) for synthesis of the high molecular weight star-shaped ROMP polymers with more branching, unimodal molecular weight distributions have been explored in detail. The method (reacting CL with NBE in the core formation step) under highly diluted conditions afforded the high molecular weight polymers with unimodal molecular weight distributions.

Ring Opening Metathesis Polymerization of Bicyclic α,β‐Unsaturated Anhydrides for Ready‐to‐be‐grafted Polymers Having Tailored pH‐Responsive Degradability

AbstractPolymers having α,β‐unsaturated anhydrides as repeating units were synthesized by ring opening metathesis polymerization (ROMP). The anhydride moieties were ready‐to‐be‐grafted with amines to form acid‐labile cis‐α,β‐unsaturated acid amide linkages. The pH‐responsive reversible de‐grafting can be controlled by changing the intramolecular accessibility between acid and amide groups. The alendronate‐grafted ROMP polymers showed distinct pH‐dependent cytotoxicity according to the anhydride structures.

Ring Opening Metathesis Polymerization of Bicyclic α,β-Unsaturated Anhydrides for Ready-to-be-grafted Polymers Having Tailored pH-Responsive Degradability.

Polymers having α,β-unsaturated anhydrides as repeating units were synthesized by ring opening metathesis polymerization (ROMP). The anhydride moieties were ready-to-be-grafted with amines to form acid-labile cis-α,β-unsaturated acid amide linkages. The pH-responsive reversible de-grafting can be controlled by changing the intramolecular accessibility between acid and amide groups. The alendronate-grafted ROMP polymers showed distinct pH-dependent cytotoxicity according to the anhydride structures.

Preparation and characterization of new nanocomposite polymer films containing NiO nanofillers

ABSTRACTNanocomposite solid polymer films based on the poly(exo‐N‐phenyl‐7‐oxanorbornene‐5,6‐dicarboximide) (PPhONDI)/LiClO4/NiO system have been designed, and the effect of inorganic NiO nanofiller in different amounts on the film properties has been examined. The exo‐PPhONDI/LiClO4/NiO polymer system is the first solid nanocomposite polymer electrolyte film example based on a ring‐opening metathesis polymerization (ROMP) host polymer. The NiO nanoparticles were prepared by two‐step chemical syntheses, and the thermoplastic host polymer, exo‐PPhONDI, was synthesized via ROMP. Composite polymer films were prepared by the solution‐casting method. The amount of nanoparticles was varied from 1 to 15 wt % of NiO. The conductivity of the nanocomposite solid polymer systems was influenced by the NiO nanofiller concentration. The composite films based on exo‐PPhONDI ROMP polymer with the highest conductivity were achieved for the composition with 8 wt % of NiO nanofiller and 10 wt % of LiClO4 dopant. The prepared films were characterized using X‐ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy (SEM). The SEM results showed that the filler was well distributed in the polymer matrix. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45938.

Synthesis of phosphorus‐ and phenyl‐based ROMP polymers and investigation of their effects on the thermomechanical and flammability properties of a polypropylene–IFR system

ABSTRACTIn this study, we present an approach for the synthesis of novel phosphorous‐ or phenyl‐ containing polymers, 2phenyl, 3phospho, and 2phenyl‐co‐3phospho, derived from ring‐opening metathesis polymerization (ROMP), to reduce the flammability of polypropylene (PP). The composites were processed by melt‐blending ROMP polymers and octaphenyl–polyhedral oligomeric silsesquioxane with PP/intumescent flame retardant (IFR) compounds at different compositions. The composites were characterized by limiting oxygen index (LOI), UL‐94, and mechanical tests as well as thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The molecular structures of phosphorous‐ and phenyl‐containing polymers were proved by 1H‐NMR, 13C‐NMR, and Fourier transform infrared spectroscopy. The online rheological measurements indicated that the addition of additives to the PP/IFR system increased the melt viscosity of the compounds regardless of the type. The DSC analysis showed that the addition of ROMP polymers to the PP/IFR system influenced the crystal perfection and degree of crystallization. TGA analysis of the composites revealed that the addition of ROMP polymers to PP/IFR compounds deteriorated the thermal stability as the amount of phosphorus increased in the matrix. Dynamic mechanical properties such as storage modulus (E′) and loss modulus (E″) of the composites were lowered by the addition of ROMP polymers. The LOI and UL‐94 rating of PP/IFR were enhanced by the addition of ROMP polymers. It was successfully demonstrated that the novel phosphorous‐ or phenyl‐containing polymers were highly potent additives in optimizing the flammability of PP composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45998.

Coil‐helix and sheet‐helix block copolymers via macroinitiation from telechelic ROMP polymers

ABSTRACTCoil‐helix and sheet‐helix block copolymers are synthesized by combining the ring‐opening metathesis polymerization (ROMP) of norbornene or paracyclophanediene with the anionic polymerization of phenyl isocyanide. Key to the design is the use of an μ‐ethynyl palladium (II) functionalized chain‐transfer agent (CTA) that can be exploited in a stepwise manner for the termination of ROMP and the initiation of the anionic polymerization. Both the coil‐ and sheet‐macroinitiators, and the ensuing covalent block copolymers, are analyzed using 1H NMR spectroscopy and gel‐permeation chromatography. In all cases, the Pd‐end group is maintained and all polymers demonstrate a monomodal distribution with dispersities (Đ) of 1.1–1.4. The resulting helix‐coil and helix‐sheet block copolymers formed by the macroinitiation route still demonstrate their intrinsic properties (fluorescence, preferential helix‐sense). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2991–2998