Grubbs’ and Schrock’s Catalysts, Ring Opening Metathesis Polymerization and Molecular Brushes—Synthesis, Characterization, Properties and Applications

Nikovia C., Theodoridis L., Alexandris S., Bilalis P., Hadjichristidis N., Floudas G., Pitsikalis M.

Statistical and block copolymerization of poly(l-lactide) (PLLA) and poly(e-caprolactone) (PCL) macromonomers having an end norbornenyl group was performed via ring-opening metathesis polymerization (ROMP) to produce the corresponding statistical and block brush copolymers consisting of PLLA and PCL side chains on a polynorbornene (PNBE) backbone. The molecular characteristics of the macromolecular brushes were determined by 1H NMR spectroscopy and size exclusion chromatography equipped with various detectors. These complex topologies allow addressing important questions on the physics of semicrystalline polymers. These include the role of (i) a doubly grafted PCL or PLLA chain on a NBE moiety (in the macromonomers) and the role of (ii) brush architecture on the crystallization behavior and dynamics of block and statistical copolymers. Significant differences were found between the macromonomers and the corresponding brush copolymers at the crystalline lamellar and spherulitic superstructure levels. In th...

Borodinov N., Belianinov A., Chang D., Carrillo J., Burch M.J., Xu Y., Hong K., Ievlev A.V., Sumpter B.G., Ovchinnikova O.S.

A direct visualization of molecular organization in an amorphous polymer bottlebrush system, captured with plasma etching and helium ion microscopy, is reported in this paper.

Yu L., Martin I.J., Kasi R.M., Wei M.

Biomimetic mineralization of collagen fibrils is an essential process because the mineralized collagen fibers constitute the basic building block of natural bone. To overcome the limited availability and high cost of the noncollagenous proteins (NCPs) that regulate the mineralization process of collagen, commercially available analogues were developed to replicate sequestration and templating functions of NCPs. The use of branched polymers in intrafibrillar mineralization applications has never been explored. In this work, two novel carboxyl-rich brushlike polymers, a carboxylated polyethylene glycol terpolymer (PEG-COOH) and a polyethylene glycol/poly(acrylic acid) copolymer (PEG-PAA), were synthesized and modified to mimic the sequestration function of NCPs to induce intrafibrillar mineralization of collagen fibrils. It was found that these synthetic brushlike polymers are able to induce intrafibrillar mineralization by stabilizing the amorphous calcium phosphate (ACP) nanoprecursors and subsequently facilitating the infiltration of ACP into the gap zone of collagen microfibrils. Moreover, the weight ratios of mineral to collagen in the mineralized collagen fibrils in the presence of these brushlike polymers were 2.17 ± 0.07 for PEG-COOH and 2.23 ± 0.03 for PEG-PAA, while it is only 1.81 ± 0.21 for linear PAA. Plausible mineralization mechanisms using brushlike polymers are proposed that offer significant insight into the understanding of collagen mineralization induced by synthetic NCP analogues.

Arrington K.J., Radzinski S.C., Drummey K.J., Long T.E., Matson J.B.

Dynamically cross-linkable bottlebrush polymer adhesives were synthesized by the grafting-from strategy through a combination of ring-opening metathesis polymerization (ROMP) and photoiniferter polymerization. A norbornene-containing trithiocarbonate was first polymerized by ROMP to form the bottlebrush polymer backbone; this was followed by blue-light-mediated photoiniferter polymerization of butyl acrylate initiated by the poly(trithiocarbonate) to form the bottlebrush polymer. This strategy afforded well-defined bottlebrush polymers with molar masses in excess of 11 000 kg/mol. For un-cross-linked bottlebrush polymers, 180° peel tests revealed a cohesive failure mode and showed similar peel strengths (∼30 g/mm) regardless of the backbone polymer degree of polymerization (DP). The bottlebrush polymers were then treated with butylamine to remove the trithiocarbonate, liberating thiols on each side-chain terminus. In the presence of oxygen, these thiols readily cross-linked via disulfide bond formation. The cross-linked bottlebrush polymers with a backbone DP of 400 showed a greater than sixfold improvement in peel strength, whereas those with a backbone DP of 100 exhibited a twofold enhancement compared with un-cross-linked samples along with a change to adhesive failure. Triphenylphosphine readily reduced the disulfide bonds, effectively removing all cross-links in the bottlebrush network and allowing for recasting of the adhesive, which showed similar adhesive and rheological properties to the original un-cross-linked samples.

Mah A.H., Mei H., Basu P., Laws T.S., Ruchhoeft P., Verduzco R., Stein G.E.

The swelling of surface-attached polymer networks (he/h) is reduced with increased branching of the primary polymer.

Mah A.H., Afzali P., Qi L., Pesek S., Verduzco R., Stein G.E.

Thin films of immiscible polymer blends will undergo phase separation into large domains, but this behavior can be suppressed with additives that accumulate and adhere at the polymer/polymer interface. Herein, we describe the phase behavior of polystyrene/poly(methyl methacrylate) (PS/PMMA) blends with 20 vol % of a bottlebrush additive, where the bottlebrush has poly(styrene-r-methyl methacrylate) side chains with 61 mol % styrene. All blends are cast into films and thermally annealed above the glass transition temperature. The phase-separated structures are measured as a function of time with atomic force microscopy and optical microscopy. We demonstrate that subtle changes in bottlebrush architecture and homopolymer chain lengths can have a large impact on phase behavior, domain coarsening, and domain continuity. The bottlebrush additives are miscible with PS under a broad range of conditions. However, these additives are only miscible with PMMA when the bottlebrush backbones are short or when the PMMA...

Cheng L., Gadelrab K.R., Kawamoto K., Yager K.G., Johnson J.A., Alexander-Katz A., Ross C.A.

The self-assembly of block copolymers (BCPs) with novel architectures offers tremendous opportunities in nanoscale patterning and fabrication. Here, the thin film morphology, annealing kinetics, and topographical templating of an unconventional Janus-type "PS- branch-PDMS" bottlebrush copolymer (BBCP) are described. In the Janus-type BBCP, each segment of the bottlebrush backbone connects two immiscible side chain blocks. Thin films of a Janus-type BBCP with Mn = 609 kg/mol exhibited 22 nm period cylindrical microdomains with long-range order under solvent vapor annealing, and the effects of as-cast film thickness, solvent vapor pressure, and composition of the binary mixture of solvent vapors are described. The dynamic self-assembly process was characterized using in situ grazing-incidence X-ray scattering. Templated self-assembly of the BBCP within lithographically patterned substrates was demonstrated, showing distinct pattern orientation and dimensions that differ from conventional BCPs. Self-consistent field theory is used to elucidate details of the templated self-assembly behavior within confinement.

Ahn S., Nam J., Zhu J., Lee E., Michael Kilbey S.

Solution self-assembly of P3HT-containing copolymers was tailored effectively via bottlebrush architecture, particularly by tuning its side chain arrangement as well as copolymer composition.

Rokhlenko Y., Kawamoto K., Johnson J.A., Osuji C.O.

We explore the morphology and phase behavior of branched diblock macromonomers and their polymers. A series of macromonomers was synthesized based on a disubstituted norbornene. The first branch consists of polydimethylsiloxane (PDMS) while the second branch is a quasi-mesogenic structure incorporating one or more cyanobiphenyl (CB) moieties. Bottlebrush polymers with varying degrees of polymerization were prepared by “graft-through” ring-opening metathesis of the macromonomers. The molecules in the resulting library of macromonomers and bottlebrush polymers self-assemble to form classically observed microphase-separated structures, including spheres, hexagonally packed cylinders, bicontinuous gyroid, and lamellae. The systematic variation of molecular structure, molecular weight of each branch, and degree of polymerization of the polymers results in a diverse set of structures and properties. We report the observation of well-ordered lamellae and cylinders with d-spacings as low as 6.1 and 8.0 nm, respec...

Nguyen H.V., Gallagher N.M., Vohidov F., Jiang Y., Kawamoto K., Zhang H., Park J.V., Huang Z., Ottaviani M.F., Rajca A., Johnson J.A.

The polymerization of functional monomers provides direct access to functional polymers without need for postpolymerization modification; however, monomer synthesis can become a bottleneck of this approach. New methods that enable rapid installation of functionality into monomers for living polymerization are valuable. Here, we report the three-step convergent synthesis (two-step longest linear sequence) of a divalent exo-norbornene imide capable of efficient coupling with various nucleophiles and azides to produce diversely functionalized branched macromonomers optimized for ring-opening metathesis polymerization (ROMP). In addition, we describe an efficient iterative procedure for the synthesis of tri-and tetra-valent branched macromonomers. We demonstrate the use of these branched macromonomers for the synthesis of Janus bottlebrush block copolymers as well as for the generation of bottlebrush polymers with up to three conjugated small molecules per repeat unit. This work significantly expands the scalability and diversity of nanostructured macromolecules accessible via ROMP.

Ndaya D., Bosire R., Mahajan L., Huh S., Kasi R.

The fabrication of mechanically robust nanoporous polymeric membrane materials with aligned, accessible functionalized nanopores is extremely important for many applications.

Adamiak L., Pendery J., Sun J., Iwabata K., Gianneschi N.C., Abbott N.L.

Interfacial assemblies formed by polymeric amphiphiles at aqueous interfaces of thermotropic liquid crystals (LCs) can trigger multiscale changes in the organization of the LCs in response to recognition events. However, we have a limited understanding of the rules governing the rational design of LC-integrated polymeric amphiphiles. Herein, we report the synthesis of families of amphiphilic polymers that differ in (i) side-chain molecular structure, (ii) polymer architecture, and (iii) copolymer composition. We used this library in experiments to establish structure–property relationships relevant to the design of multifunctional polymers that can amplify and transduce biomolecular recognition events into optically detectable, macroscopic ordering transitions in LCs. We then utilized these structure–property relationships to guide the design of a peptide–polymer amphiphile (PPA) that assembles at the interface of LC droplets. Enzymatic cleavage of PPA-coated LC droplets by thermolysin directly triggered ...

Yu Y., Chae C., Kim M., Seo H., Grubbs R.H., Lee J.

A facile and efficient synthetic grafting-through strategy for preparing well-defined bottlebrush block copolymers (BBCPs) was developed through a combination of living anionic polymerization (LAP) and ring-opening metathesis polymerization (ROMP). ω-End-norbornyl polystyrene (NPSt) and poly(4-tert-butoxystyrene) (NPtBOS) were synthesized by LAP using terminator of chlorine moiety containing silane-protecting amine and coupled with a subsequent amidation using norbornyl activated ester. Bottlebrush homopolymers of NPSt were obtained by ROMP with ultrahigh molecular weights (MWs, Mw = 2928 kDa) and narrow molecular weight distributions (MWDs, Đ = 1.07) at high degree of polymerizations (DPw = 1084). Well-defined BBCPs with ultrahigh MWs (Mw ∼ 3055 kDa) and narrow MWDs (Đ ∼ 1.13) were synthesized through sequential ROMP of NPSt with NPtBOS. The effect of ultrahigh MWs was investigated by self-assembly of the BBCPs in which the phase-separated BBCPs presented periodic lamellar structures and exhibited struct...

Sutthasupa S., Sanda F.

Leucine-derived norbornene monomer (1), oligo(lactic acid)-derived norborne macromonomer (2) and indomethacin-conjugated norbornene (3) were synthesized and polymerized using the Grubbs ruthenium complex as a catalyst. Macromonomer 2 was synthesized by the ring-opening polymerization of lactide using 5-norbornene-2,3-exo,exo-dimethanol as an initiator and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst. The corresponding polymers, poly(1), poly(2), poly(3) and copolymers with number-average molecular weights (Mn) ranging from 14 000 to 360 000 were obtained in 73–95% yields. Poly(2) formed scaffolds by simply drying under reduced pressure presumably due to the brush-like structure causing entanglement of the polymer chains. The compressive strength of poly(2) scaffold increased as increasing the polylactide chain length. The compressive strength of the scaffolds obtained from the copolymers ranged from 0.222 to 0.587 MPa in accordance with the monomer unit ratios. SEM revealed the presence of pores around 5–10 µm diameters, together with larger pores dispersed in the range of 50–300 µm diameters. TEM demonstrated the presence of polymer networks. The conjugated indomethacin was gradually released by incubation under acidic condition (pH 5.7) at 37 °C. The results of % cell viability, release of LDH activity and cell morphology assays revealed that the obtained scaffolds did not exhibit cytotoxicity toward HEK 293 cells.

Gopinadhan M., Choo Y., Mahajan L.H., Ndaya D., Kaufman G., Rokhlenko Y., Kasi R.M., Osuji C.O.

Phase behavior and dynamics of a LC block copolymer are manipulated by labile mesogens to enable alignment, photopatterning and nanopore orientation at low magnetic fields.

Wu L., Glebe U., Kwok K.T., Sun J., Lam J.W., Tang B.Z.

AbstractBottlebrush polymers, characterized by densely grafted side chains along a central backbone, have gained significant interest due to their unique properties in bulk and solution states. Despite extensive research, a comprehensive understanding of the internal crowdedness within single polymer chains in dilute solutions remains challenging, and direct evidence to visualize and manifest this effect is scarce. Aggregation‐induced emission (AIE) offers a novel method to address this challenge. To achieve this, a vinyl‐derivatized AIE monomer was polymerized using atom transfer radical polymerization (ATRP) in a controlled way. Afterward, the end group of the synthesized polymer chain was transformed to azide, which was coupled with an alkyne‐derivatized norbornene unit using click chemistry to produce the macromonomer. Ring‐opening metathesis polymerization (ROMP) of the norbornenyl macromonomer using Grubbs catalyst, (H2IMes)(pyr)2(Cl)2Ru = CHPh (G3), resulted in well‐defined bottlebrush polymers in a highly efficient way. We studied the polymerization behavior and characterized the single chain conformation of the bottlebrush polymers in dilute solution together with coarse‐grained molecular dynamics (CG‐MD) simulation. Photoluminescence investigation of the bottlebrush polymers in dilute solution revealed the expected AIE phenomenon, thus verifying the steric crowding effects within bottlebrush polymers. This work bridges AIE technology with polymer science and especially bottlebrush polymers. By doing this, our research not only broadens the bottlebrush polymer library but also provides insights into bottlebrush polymer chain study for potential applications.

Wu L., Glebe U., Kwok K.T., Sun J., Lam J.W., Tang B.Z.

AbstractBottlebrush polymers, characterized by densely grafted side chains along a central backbone, have gained significant interest due to their unique properties in bulk and solution states. Despite extensive research, a comprehensive understanding of the internal crowdedness within single polymer chains in dilute solutions remains challenging, and direct evidence to visualize and manifest this effect is scarce. Aggregation‐induced emission (AIE) offers a novel method to address this challenge. To achieve this, a vinyl‐derivatized AIE monomer was polymerized using atom transfer radical polymerization (ATRP) in a controlled way. Afterward, the end group of the synthesized polymer chain was transformed to azide, which was coupled with an alkyne‐derivatized norbornene unit using click chemistry to produce the macromonomer. Ring‐opening metathesis polymerization (ROMP) of the norbornenyl macromonomer using Grubbs catalyst, (H2IMes)(pyr)2(Cl)2Ru = CHPh (G3), resulted in well‐defined bottlebrush polymers in a highly efficient way. We studied the polymerization behavior and characterized the single chain conformation of the bottlebrush polymers in dilute solution together with coarse‐grained molecular dynamics (CG‐MD) simulation. Photoluminescence investigation of the bottlebrush polymers in dilute solution revealed the expected AIE phenomenon, thus verifying the steric crowding effects within bottlebrush polymers. This work bridges AIE technology with polymer science and especially bottlebrush polymers. By doing this, our research not only broadens the bottlebrush polymer library but also provides insights into bottlebrush polymer chain study for potential applications.

Amorim K.A., Martins V.C., Lima-Neto B.S.

Nayab S., Lee H., Lee S.

Rekha Rout S., Kenguva G., Mansuri S., R.Manu K., Dandela R., Pramanik N.B.

Sarkar R., Pal A., Saha B.

Serkhacheva N.S., Prokopov N.I., Lysenko E.A., Kozhunova E.Y., Chernikova E.V.

Polymerization-induced self-assembly (PISA) is a powerful and versatile technique for producing colloidal dispersions of block copolymer particles with desired morphologies. Currently, PISA can be carried out in various media, over a wide range of temperatures, and using different mechanisms. This method enables the production of biodegradable objects and particles with various functionalities and stimuli sensitivity. Consequently, PISA offers a broad spectrum of potential commercial applications. The aim of this review is to provide an overview of the current state of rational synthesis of block copolymer particles with diverse morphologies using various PISA techniques and mechanisms. The discussion begins with an examination of the main thermodynamic, kinetic, and structural aspects of block copolymer micellization, followed by an exploration of the key principles of PISA in the formation of gradient and block copolymers. The review also delves into the main mechanisms of PISA implementation and the principles governing particle morphology. Finally, the potential future developments in PISA are considered.

Clarke B.R., Witt C.L., Ilton M., Crosby A.J., Watkins J.J., Tew G.N.

AbstractBottlebrush networks (BBNs) are an exciting new class of materials with interesting physical properties derived from their unique architecture. While great strides have been made in our fundamental understanding of bottlebrush polymers and networks, an interdisciplinary approach is necessary for the field to accelerate advancements. This perspective aims to act as a primer to BBN chemistry and physics for both new and current members of the community. In addition to providing an overview of contemporary BBN synthetic methods, we developed a workflow and desktop application (LengthScale), enabling bottlebrush physics to be more approachable. We conclude by addressing several topical issues and asking a series of pointed questions to stimulate conversation within the community.

Clarke B.R., Witt C.L., Ilton M., Crosby A.J., Watkins J.J., Tew G.N.

AbstractBottlebrush networks (BBNs) are an exciting new class of materials with interesting physical properties derived from their unique architecture. While great strides have been made in our fundamental understanding of bottlebrush polymers and networks, an interdisciplinary approach is necessary for the field to accelerate advancements. This perspective aims to act as a primer to BBN chemistry and physics for both new and current members of the community. In addition to providing an overview of contemporary BBN synthetic methods, we developed a workflow and desktop application (LengthScale), enabling bottlebrush physics to be more approachable. We conclude by addressing several topical issues and asking a series of pointed questions to stimulate conversation within the community.

Adeli Y., Raman Venkatesan T., Mezzenga R., Nüesch F.A., Opris D.M.

Mantzara D., Katara A., Panteli M., Stavrakaki I.G., Plachouras N.V., Choinopoulos I., Pitsikalis M.

AbstractStatistical and block copolymers of n‐hexyl isocyanate (HIC) and 2‐chloroethyl isocyanate (ClEtIC) were synthesized via cοοrdination polymerization employing the half‐titanocene complex [(η5‐C5H5)((S)‐2‐Bu‐O)TiCl2] as initiator. The complex, bearing a chiral substituent, led to optically active products, as confirmed by circular dichroism measurements. The molecular characterization of all products was carried out by NMR and IR spectroscopy and size exclusion chromatography (SEC), while their thermal stability was investigated through differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and differential thermogravimetry (DTG). The reactivity ratios of the two monomers were determined using various graphical methods, as well as the COPOINT program, according to the terminal copolymerization model. Structural parameters, such as the dyad monomer sequences and the mean sequence lengths were calculated as well. In addition, the kinetics of the thermal degradation of the statistical copolymers was studied, and the activation energies of the thermal degradation were calculated employing the Kissinger, Ozawa–Flynn–Wall (OFW), and Kissinger–Akahira–Sunose (KAS) methods. The block copolymers were synthesized by sequential addition of monomers starting from the polymerization of HIC. Well‐defined products were obtained in a controlled way as revealed by SEC, IR, and NMR measurements.

Urquhart R.J., Tuttle T.

Clarke B.R., Tew G.N.

Chen R., Smith J.D., Osores N.N., Gopalan P.

AbstractWe report the synthesis of a Y‐shaped inimer that contains two orthogonal initiators for ATRP and NMP. The inimer is synthesized through a one‐pot multi‐component reaction that vastly simplifies the typically cumbersome synthesis of similar compounds. The Y‐inimer has the versatility to be homopolymerized into a backbone for A/B Janus bottlebrush synthesis or copolymerized with glycidyl methacrylate (GMA) and cross‐linked into an ultra‐thin coating for mixed A/B brush growth from planar surfaces. Importantly, the Y‐shaped nature of the inimer ensures growth of A and B brushes are consistently in a 1:1 ratio. We demonstrate the application of the Y‐inimer in the synthesis of a PMMA/PS Janus bottlebrush as well as two different mixed A/B polymer brushes, one with the ability to microphase separate, and a second mixed polyelectrolyte brush with opposite charges. The inimer is compatible with various A/B monomer systems and offers a universal approach to the “grafting‐from” polymerization of dual vinyl polymer side chains. This study provides a unique way of utilizing multi‐component reactions in polymer chemistry to access complex functional architectures.

Arel I., Ay A., Wang J., Gil-Herrera L.K., Dumanli A.G., Akbulut O.