Post-functionalization of a ROMP polymer backbone via radical thiol-ene coupling chemistry

High-Refractive-Index Cross-Linked Cyclic Olefin Polymers with Excellent Transparency via Thiol-Ene Click Reaction

High-refractive-index polymers are important optical materials in optoelectronics. Conventional cyclic olefin polymers (COPs), possessing many excellent optical properties, are a class of highly promising optical materials; however, one of the greatest obstacles is their low refractive index of n = 1.52-1.54. Here, one efficient strategy of first incorporating high molar refraction groups, including carbazolyl and indolyl moieties, into unsaturated COPs via ring-opening metathesis polymerization (ROMP) and then introducing another high molar refraction sulfur atom by a subsequent thiol-ene click reaction is presented. The obtained cross-linked COPs bearing both an aromatic group and sulfur possess significantly higher refractive indices (n = 1.611-1.684 at 589 nm) and highly optical transparency (approximately 95%) in the range of vis-NIR. This provides a way toward potential applications of new-generation optical materials.

Direct-ink-write cross-linkable bottlebrush block copolymers for on-the-fly control of structural color

Additive manufacturing capable of controlling and dynamically modulating structures down to the nanoscopic scale remains challenging. By marrying additive manufacturing with self-assembly, we develop a UV (ultra-violet)-assisted direct ink write approach for on-the-fly modulation of structural color by programming the assembly kinetics through photo-cross-linking. We design a photo-cross-linkable bottlebrush block copolymer solution as a printing ink that exhibits vibrant structural color (i.e., photonic properties) due to the nanoscopic lamellar structures formed post extrusion. By dynamically modulating UV-light irradiance during printing, we can program the color of the printed material to access a broad spectrum of visible light with a single ink while also creating color gradients not previously possible. We unveil the mechanism of this approach using a combination of coarse-grained simulations, rheological measurements, and structural characterizations. Central to the assembly mechanism is the matching of the cross-linking timescale with the assembly timescale, which leads to kinetic trapping of the assembly process that evolves structural color from blue to red driven by solvent evaporation. This strategy of integrating cross-linking chemistry and out-of-equilibrium processing opens an avenue for spatiotemporal control of self-assembled nanostructures during additive manufacturing.

Dithiophosphoric Acids for Polymer Functionalization

Dithiophosphoric acids (DTPAs) are an intriguing class of compounds that are sourced from elemental sulfur and white phosphorus and are prepared from the reaction of phosphorus pentasulfide with alcohols. The electrophilic addition of DTPAs to alkenes and unsaturated olefinic substrates is a known reaction, but has not been applied to polymer synthesis and polymer functionalization. We report on the synthesis and application of DTPAs for the functionalization of challenging poly-enes, namely polyisoprene (PI) and polynorbornene (pNB) prepared by ring-opening metathesis polymerization (ROMP). The high heteroatom content within DTPA moieties impart intriguing bulk properties to poly-ene materials after direct electrophilic addition reactions to the polymer backbone introducing DTPAs as side chain groups. The resulting materials possess both enhanced optical and flame retardant properties vs the poly-ene starting materials. Finally, we demonstrate the ability to prepare crosslinked polydiene films with di-functional DTPAs, where the crosslinking density and thermomechanical properties can be directly tuned by DTPA feed ratios.

Significance of Polymers with “Allyl” Functionality in Biomedicine: An Emerging Class of Functional Polymers

In recent years, polymer-based advanced drug delivery and tissue engineering have grown and expanded steadily. At present, most of the polymeric research has focused on improving existing polymers or developing new biomaterials with tunable properties. Polymers with free functional groups offer the diverse characteristics needed for optimal tissue regeneration and controlled drug delivery. Allyl-terminated polymers, characterized by the presence of a double bond, are a unique class of polymers. These polymers allow the insertion of a broad diversity of architectures and functionalities via different chemical reactions. In this review article, we shed light on various synthesis methodologies utilized for generating allyl-terminated polymers, macromonomers, and polymer precursors, as well as their post-synthesis modifications. In addition, the biomedical applications of these polymers reported in the literature, such as targeted and controlled drug delivery, improvement i aqueous solubility and stability of drugs, tissue engineering, and antimicrobial coatings, are summarized.

One-pot synthesis of linear triblock terpolymers and their aqueous self-assembly

Compartmentalized micelles are prepared through the self-assembly of linear triblock terpolymers containing hydrophilic (H), lipophilic (L), and fluorophilic (F) domains.

Rapid Processing of Bottlebrush Coatings through UV-Induced Cross-Linking

Bottlebrush polymers can be used to introduce novel surface properties including hydrophilicity, stimuli-responsiveness, and reduced friction forces. However, simple, general, and efficient approaches to cross-linking bottlebrush polymer films and coatings are limited. Here, we report that bottlebrush polymers with an unsaturated polynorbornene backbone and thiol-terminated side chains can be cross-linked on demand by UV irradiation to produce uniform and insoluble bottlebrush polymer coatings. To quantify the kinetics and efficiency of cross-linking by UV exposure (254 nm), we measured the normalized residual thickness (NRT) of bottlebrush and linear polymer films after UV exposure and solvent washing. For bottlebrush polymers with thiol-terminated polystyrene (PS) side chains, the NRT exceeded 60% for a UV dose of 1.0 J/cm², while unfunctionalized linear PS required a dose of 7.9 J/cm² to achieve similar NRT values. Rapid UV-induced cross-linking of the bottlebrush PS was attributed to the thiol-ene coupling of the thiol-terminated side chains with the unsaturated polynorbornene backbones, as demonstrated through FTIR measurements and control studies involving bottlebrush polymers with saturated backbones. To establish the broader applicability of this approach, UV-induced cross-linking was demonstrated for thin films of bottlebrush polymers with thiol-terminated poly(methyl acrylate) (BB-PMMA-SH) side chains and those with poly(ethylene glycol) (BB-PEG) and poly(lactic acid) (BB-PLA) side chains which do not contain thiol end groups. UV-induced cross-linking of BB-PEG and BB-PLA films required the use of a multifunctional thiol additive. Finally, we demonstrated that bottlebrush polymer multilayers can be fabricated through sequential deposition and UV-induced cross-linking of different bottlebrush polymer chemistries. The cross-linking process outlined in this work is simple, general, and efficient and produces solvent-resistant coatings that preserve the unique properties and functions of bottlebrush polymers.

Controlling Polymer Composition in Organocatalyzed Photoredox Radical Ring-Opening Polymerization of Vinylcyclopropanes

Although radical polymerizations are among the most prevalent methodologies for the synthesis of polymers with diverse compositions and properties, the intrinsic reactivity and selectivity of radical addition challenge the ability to impart control over the polymerization propagation and produce polymers with defined microstructure. Vinylcyclopropanes (VCPs) can be polymerized through radical ring-opening polymerization to produce polymers possessing linear (l) or cyclic (c) repeat units, providing the opportunity to control polymer structure and modify the polymer properties. Herein, we report the first organocatalyzed photoredox radical ring-opening polymerization of a variety of functionalized VCP monomers, where high monomer conversions and spatial and temporal control were achieved to produce poly(VCPs) with predictable molecular weight and low dispersity. Through manipulating polymerization concentration and temperature, tunable l or c content was realized, allowing further investigation of thermal and viscoelastic materials properties associated with these two distinct compositions. Unexpectedly, the photoredox catalysis enables a postpolymerization modification that converts l content into the c content. Combined experimental and computational studies suggested an intramolecular radical cyclization pathway, where cyclopentane and cyclohexane repeat units are likely formed.

Templated Synthesis of End-Functionalized Graphene Nanoribbons through Living Ring-Opening Alkyne Metathesis Polymerization

Atomically precise bottom-up synthesized graphene nanoribbons (GNRs) are promising candidates for next-generation electronic materials. The incorporation of these highly tunable semiconductors into complex device architectures requires the development of synthetic tools that provide control over the absolute length, the sequence, and the end groups of GNRs. Here, we report the living chain-growth synthesis of chevron-type GNRs (cGNRs) templated by a poly-(arylene ethynylene) precursor prepared through ring-opening alkyne metathesis polymerization (ROAMP). The strained triple bonds of a macrocyclic monomer serve both as the site of polymerization and the reaction center for an annulation reaction that laterally extends the conjugated backbone to give cGNRs with predetermined lengths and end groups. The structural control provided by a living polymer-templated synthesis of GNRs paves the way for their future integration into hierarchical assemblies, sequence-defined heterojunctions, and well-defined single-GNR transistors via block copolymer templates.

Norbornene, norbornadiene and their derivatives: promising semi-products for organic synthesis and production of polymeric materials

The methods for synthesis of promising norbornene monomers from norbornadiene and quadricyclane are summarized. A strategy for their synthesis is discussed, combining theoretical and experimental approaches to the selection of catalysts and the conditions for carrying out stereoselective reactions. The mechanisms of catalytic reactions of synthesis of norbornene monomers, as well as the progress in the macromolecular design of functional polymeric materials based on them, are considered. The data on industrial processes of production of polynorbornenes and areas of their use are presented.

The bibliography includes 297 references.

Rapid, Regioselective Living Ring-Opening Metathesis Polymerization of Bio-Derivable Asymmetric Tricyclic Oxanorbornenes

The synthesis of a range of alkyl esters (methyl, n-butyl, and n-decyl) prepared via Steglich esterification of the thermodynamically controlled exo, exo Diels-Alder adduct of furfuryl alcohol and maleic anhydride is reported. Subsequent ring-opening metathesis polymerization of these bio-derivable tricyclic oxanorbornene analogs delivers polymers with targeted molar mass and low molar mass dispersity. The polymerizations are rapid with complete monomer conversion achieved within 15 min. Significantly, the presence of the cyclic lactone at the bridgehead of these monomers leads to polymers with high regioregularity (>85% head-to-tail) and high stereoregularity (>75% trans). The resultant polymers display both high thermal stability and high glass transition temperatures. This new class of oxanorbornene monomer, accessed from bio-derivable furfuryl alcohol and maleic anhydride, may be further tailored to incorporate a range of functional moieties. Furthermore, the exceptional properties of the derived polymers indicate potential in a range of applications.

Expanding the ROMP Toolbox: Synthesis of Air-Stable Benzonorbornadiene Polymers by Aryne Chemistry

Benzonorbornadiene polymers synthesized by ring-opening metathesis polymerization (ROMP) are typically prone to oxidation at the benzylic/allylic position under ambient conditions. Accordingly, the use of benzonorbornadiene polymers in practical applications has remained limited. In this manuscript, we report the synthesis of poly(benzonorbornadiene) polymers using a strategic blend of benzyne chemistry and ROMP. Through a comparative study, we show that substitution at the benzylic/allylic position prevents oxidative deformation, yet does not inhibit polymerization by common ruthenium catalysts with good control over molecular weight dispersity. We expect the benzyne/ROMP reaction sequence will allow easy access to air-stable benzonorbornadiene polymers for various applications.

Functionalized Nanofiber Meshes Enhance Immunosorbent Assays

Three-dimensional substrates with high surface-to-volume ratios and subsequently large protein binding capacities are of interest for advanced immunosorbent assays utilizing integrated microfluidics and nanosensing elements. A library of bioactive and antifouling electrospun nanofiber substrates, which are composed of high-molecular-weight poly(oxanorbornene) derivatives, is described. Specifically, a set of copolymers are synthesized from three 7-oxanorbornene monomers to create a set of water insoluble copolymers with both biotin (bioactive) and triethylene glycol (TEG) (antifouling) functionality. Porous three-dimensional nanofiber meshes are electrospun from these copolymers with the ability to specifically bind streptavidin while minimizing the nonspecific binding of other proteins. Fluorescently labeled streptavidin is used to quantify the streptavidin binding capacity of each mesh type through confocal microscopy. A simplified enzyme-linked immunosorbent assay (ELISA) is presented to assess the protein binding capabilities and detection limits of these nanofiber meshes under both static conditions (26 h) and flow conditions (1 h) for a model target protein (i.e., mouse IgG) using a horseradish peroxidase (HRP) colorimetric assay. Bioactive and antifouling nanofiber meshes outperform traditional streptavidin-coated polystyrene plates under flow, validating their use in future advanced immunosorbent assays and their compatibility with microfluidic-based biosensors.

Multiblock Copolymers by Thiol Addition Across Norbornene

Multiblock copolymers, composed of different combinations and number of blocks, offer appreciable opportunities for new advanced materials. However, exploring this parameter space using traditional block copolymer synthetic techniques, such as living polymerization of sequential blocks, is time-consuming and requires stringent conditions. Using thiol addition across norbornene chemistry, we demonstrate a simple synthetic approach to multiblock copolymers that produces either random or alternating architectures, depending on the choice of reactants. Past reports have highlighted the challenges associated with using thiol-ene chemistry for polymer-polymer conjugation; however, using norbornene as the "ene" yielded multiblock copolymers at least four or five blocks. Preparation of new multiblock copolymers containing two or three block chemistries highlights the versatility of this new approach. These materials were thermally stable and showed microphase separation according to characterization by DSC, SAXS, and AFM. This chemical platform offers a facile and efficient route to exploring the many possibilities of multiblock copolymers.

Combining ring-opening metathesis polymerization and thiol-ene coupling chemistries: facile access to novel functional linear and nonlinear macromolecules

The aim of this article is to highlight recent examples in which two powerful synthetic tools, namely ring-opening metathesis polymerization (ROMP) and thiol-ene (including the thiol-Michael variant) click chemistry have been combined to facilitate the preparation of novel functional materials of varying topology.

ROMP (co)polymers with pendent alkyne side groups: post-polymerization modification employing thiol–yne and CuAAC coupling chemistries

The synthesis of a series of copolymers via ring-opening metathesis polymerization (ROMP) containing pendent trimethylsilyl-protected alkyne functional groups is described.

Thiol–ene “click” reactions and recent applications in polymer and materials synthesis: a first update

This contribution serves as an update to a previous review (Polym. Chem.2010,1, 17–36) and highlights recent applications of thiol–ene ‘click’ chemistry as an efficient tool for both polymer/materials synthesis as well as modification.

Functional α,ω-dienes via thiol-Michael chemistry: synthesis, oxidative protection, acyclic diene metathesis (ADMET) polymerization and radical thiol–ene modification

The synthesis of the novel α,ω-diene 2-(undec-10-en-1-yl)tridec-12-en-1-yl acrylate is described.