Synthesis of Comb Block Copolymers by ROMP, ATRP, and ROP and Their Assembly in the Solid State

Optimizing Chain Topology of Bottle Brush Copolymer for Promoting the Disorder-to-Order Transition

The order-disorder transitions (ODT) of core-shell bottle brush copolymer and its structural isomers were investigated by dissipative particle dynamics simulations and theoretically by random phase approximation. Introducing a chain topology parameter λ which parametrizes linking points between M diblock chains each with N monomers, the degree of incompatibility at ODT ((χN)ODT; χ being the Flory-Huggins interaction parameter between constituent monomers) was predicted as a function of chain topology parameter (λ) and the number of linked diblock chains per bottle brush copolymer (M). It was found that there exists an optimal chain topology about λ at which (χN)ODT gets a minimum while the domain spacing remains nearly unchanged. The prediction provides a theoretical guideline for designing an optimal copolymer architecture capable of forming sub-10 nm periodic structures even with non-high χ components.

From macromonomers to bottlebrush copolymers with sequence control: synthesis, properties, and applications

Bottlebrush polymers (BBPs) are a type of comb-like macromolecules with densely grafted polymeric sidechains attached to the polymer backbones, and many intriguing properties and applications have been demonstrated due to...

Shape-Changing Bottlebrush Polymers

Bottlebrush polymers (BBPs), composed of relatively short polymeric side chains densely grafted on a polymer backbone, exhibit many unique characteristics and hold promise for a variety of applications. This Perspective focuses on environmentally induced shape-changing behavior of BBPs at interface and in solution, particularly worm/star-globule shape transitions. While BBPs with a single type of homopolymer or random copolymer side chains have been shown to undergo pronounced worm-to-globule shape changes in response to external stimuli, the collapsed brushes are unstable and prone to aggregation. By introducing a second, solvophilic polymer into the side chains, either as a distinct type of side chain or as the outer block of block copolymer side chains, the collapsed brushes not only are stabilized but also create unimolecular micellar nanostructures, which can be used for, e.g., encapsulation and delivery of substances. The current challenges in the design, synthesis, and characterization of stimuli-responsive shape-changing BBPs are discussed.

Mixed Polymer Brushes for "Smart" Surfaces

Mixed polymer brushes (MPBs) are composed of two or more disparate polymers covalently tethered to a substrate. The resulting phase segregated morphologies have been extensively studied as responsive "smart" materials, as they can be reversible tuned and switched by external stimuli. Both computational and experimental work has attempted to establish an understanding of the resulting nanostructures that vary as a function of many factors. This contribution highlights state-of-the-art MPBs studies, covering synthetic approaches, phase behavior, responsiveness to external stimuli as well as novel applications of MPBs. Current limitations are recognized and possible directions for future studies are identified.

Preparation of functionalized poly(1-butene) from 1,2-polybutadiene via sequential thiol-ene click reaction and ring-opening polymerization

Poly(1-butene) is a kind of unique poly(α-olefin) material that displays exceptional creep resistance and environmental stress cracking resistance, and therefore currently finds wide application in the fields of packaging, films, pipes, etc. However, very few current researchers are paying attention to functional poly(1-butene) despite its great research significance, perhaps due to the general paucity of catalytic systems for synthesizing this material. Therefore, in the present study, we set out to develop an alternative method to prepare polar poly(1-butene)s. Specifically, 1,2-enriched poly(1,3-butadiene), used as a starting material, was partially hydrogenated to afford a quasi-poly(1-butene) polymer containing C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C double bonds. These double bonds were further modified by subjecting the quasi-poly(1-butene) polymer to a thiol-ene reaction in the presence of thiol compounds, and a series of polar poly(1-butene)s that bore significantly improved surface properties were obtained. By using hydroxyl-containing thiol compounds, ring-opening polymerization (ROP) of ε-caprolactone was further implemented. Here, polar poly(ε-caprolactone) was incorporated as side chains, and we were able to control the chain length by adjusting the feeding ratio. The water contact angles of the resultant polymers, i.e., those containing the poly(ε-caprolactone) side chains, were as low as 59.4°, indicating a greater hydrophilicity resulting from the incorporation of these side chains.

An alternative method for preparing functionalized poly(1-butene) from 1,2-polybutadiene via sequential thiol-ene click reaction and ring-opening polymerization is reported.

Order-to-Disorder Transitions in Lamellar Melt Self-Assembled Core-Shell Bottlebrush Polymers

We report the synthesis and melt self-assembly behaviors of densely grafted, core-shell bottlebrush (csBB) polymers derived from covalently linking narrow dispersity, symmetric composition ABA-type triblock polymers through their chain midpoints. Derived from sequential ring-opening polymerizations of ε-decalactone and rac-lactide initiated from 5-norbornene-2-exo,3-exo-dimethanol, poly(lactide-block-ε-decalactone-block-lactide) macromonomers (M_n = 9.2-17.8 kg/mol; Đ = 1.19-1.25) were enchained by living ring-opening metathesis polymerization (ROMP) into csBBs with backbone degrees of polymerization N_bb = 8-43. Temperature-dependent small-angle X-ray scattering (SAXS) studies indicate that the critical triblock arm degree of polymerization (N_arm) required for melt segregation decreases with increasing N_bb, leading to reductions in the accessible ordered lamellar microdomain (d) spacings. We derive a phenomenological relationship between the critical triblock arm segregation strength at the order-disorder transition (χN_arm)_ODT and N_bb to enable the future design of microphase separated core-shell bottlebrushes, which self-assemble at sub-10 nm length scales for nanolithography and nanotemplating applications.

Amphiphilic multicomponent molecular brushes

Multicomponent molecular brushes containing amphiphilic polymer moieties are promising objects of research of macromolecular chemistry. The development of stimulus-responsive systems sensitive to changes in environmental parameters, based on the molecular brushes, opens up new possibilities for their applications in medicine, biochemistry and microelectronics. The review presents the current understanding of the structures of main types of amphiphilic multicomponent brushes, depending on the chemical nature and type of coupling of the backbone and side chains. The approaches to the controlled synthesis of multicomponent molecular brushes of different architecture are analyzed. Self-assembly processes of multicomponent molecular brushes in selective solvents are considered.

The bibliography includes 259 references.

Dual Polymerizations: Untapped Potential for Biomaterials

Block copolymers with unique architectures and those that can self-assemble into supramolecular structures are used in medicine as biomaterial scaffolds and delivery vehicles for cells, therapeutics, and imaging agents. To date, much of the work relies on controlling polymer behavior by varying the monomer side chains to add functionality and tune hydrophobicity. Although varying the side chains is an efficient strategy to control polymer behavior, changing the polymer backbone can also be a powerful approach to modulate polymer self-assembly, rigidity, reactivity, and biodegradability for biomedical applications. There are many developments in the syntheses of polymers with segmented backbones, but these developments are not widely adopted as strategies to address the unique constraints and requirements of polymers for biomedical applications. This review highlights dual polymerization strategies for the synthesis of backbone-segmented block copolymers to facilitate their adoption for biomedical applications.

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

In this review, molecular brushes and other macromolecular architectures bearing a bottlebrush segment where the main chain is synthesized by ring opening metathesis polymerization (ROMP) mediated by Mo or Ru metal complexes are considered. A brief review of metathesis and ROMP is presented in order to understand the problems and the solutions provided through the years. The synthetic strategies towards bottlebrush copolymers are demonstrated and each one discussed separately. The initiators/catalysts for the synthesis of the backbone with ROMP are discussed. Syntheses of molecular brushes are presented. The most interesting properties of the bottlebrushes are detailed. Finally, the applications studied by different groups are presented.

Tailor-Made, Linear, and “Comb-Like” Polyester-Based Copolymers: Synthesis, Characterization, and Thermal Behavior of Potential 3D-Printing/Electrospinning Candidates

Tailor-made, linear, and “comb-like” poly(ε-caprolactone)-based copolymers were synthesized by employing a combination of controlled polymerization techniques. Poly(dimethylsiloxane-block-ε-caprolactone) copolymers (SCL#) were synthesized by a combination of anionic and ring-opening polymerization (ROP), whereas “comb-like” poly(hydroxyethylmethacrylate-co-(hydroxyethylmethacrylate-graft-ε-caprolactone)-block-ε-caprolactone) (HEMACL#) were synthesized through simultaneous ROP and reversible addition fragmentation chain transfer (RAFT) polymerization. Copolymers were characterized by hydrogen nuclear magnetic resonance (1H-NMR), size exclusion chromatography (SEC), and Fourier transform infrared (FTIR) spectroscopy. All polymers exhibited narrow molar masses distributions (Mw/Mn<1.54), and their thermal properties were analyzed by isothermal crystallization kinetics (Avrami’s theory, by using differential scanning calorimetry (DSC)) and by employing modulated thermogravimetric analysis (MTGA). The macromolecular structure exerts a noticeable effect on the PCL block behavior when compared to the PCL homopolymer, at least for the temperature range studied (16–24°C): less differences in thermal properties were observed for linear block copolymers, whereas for “comb-like” graft copolymers their final crystallization capacity strongly depends on the presence of branches. For both sets of copolymers, the decrease in the resulting melting temperatures and the increase in the half-life crystallization time values might be useful processing parameters, particularly if these copolymers are planned for using as an alternative source of 3D printing or electrospinning materials.

One-Shot Synthesis and Melt Self-Assembly of Bottlebrush Copolymers with a Gradient Compositional Profile

Morphological control plays a central role in soft materials design. Herein, we report the synthesis of a gradient bottlebrush architecture and its role in directing molecular packing in the solid state. Bottlebrush copolymers with gradient interfaces were prepared via one-shot ring-opening metathesis polymerization of exo- and endo-norbornene-capped macromonomers. Kinetic studies revealed a gradient compositional profile separating the two blocks along the backbone. Side-chain symmetric gradient bottlebrush copolymers exhibited a strong tendency to assemble into cylindrical microstructures, in contrast to their block copolymer analogs with sharp interfaces. Such exquisite architectural control of the interfacial composition affords a delicate handle to direct macromolecular assembly.

Efficient Codelivery of Paclitaxel and Curcumin by Novel Bottlebrush Copolymer-based Micelles

The novel self-assembling bottlebrush polyethylene glycol-polynorbornene-thiocresol block copolymers (PEG-PNB-TC) were synthesized by the ring opening metathesis polymerization (ROMP), followed by functionalization of the polymer backbone via the thio-bromo "click" postpolymerization strategy. The PEG-PNB-TC copolymers could easily self-assemble into the nanoscale core-shell polymeric micelles. The hydrophobic anticancer drugs, such as paclitaxel (PTX), could be loaded into their hydrophobic core to form a stable drug-loaded micelle with a superior drug loading capacity of up to ∼35% (w/w). The sustained drug release behavior of the PEG-PNB-TC micelles was observed under a simulated "sink condition". Compared with commercial PTX formulation (Taxol), the PTX-loaded PEG-PNB-TC micelles showed the enhanced in vitro cellular uptake and comparable cytotoxicity in the drug-sensitive cancer cells, while the copolymers were much safer than Cremophor EL, the surfactant used in Taxol. Furthermore, curcumin (CUR), a natural chemotherapy drug sensitizer, was successfully coloaded with PTX into the PEG-PNB-TC micelles. High drug loading capacity of the PEG-PNB-TC micelles allowed for easy adjustment of drug doses and the ratio of the coloaded drugs. The combination of PTX and CUR showed synergistic anticancer effect in both the drug mixture and drug coloaded micelles at high CUR/PTX ratio, while low CRU/PTX ratio only exhibited additive effects. The combinatorial effects remarkably circumvented the PTX resistance in the multidrug resistant (MDR) cancer cells. Due to the easy polymerization and functionalization, excellent self-assembly capability, high drug loading capability, and great stability, the PEG-PNB-TC copolymers might be a promising nanomaterial for delivery of the hydrophobic anticancer drugs, especially for combination drug therapy.

Application of Bottlebrush Block Copolymers as Photonic Crystals

Brush block copolymers are a class of comb polymers that feature polymeric side chains densely grafted to a linear backbone. These polymers display interesting properties due to their dense functionality, low entanglement, and ability to rapidly self-assemble to highly ordered nanostructures. The ability to prepare brush polymers with precise structures has been enabled by advancements in controlled polymerization techniques. This Feature Article highlights the development of brush block copolymers as photonic crystals that can reflect visible to near-infrared wavelengths of light. Fabrication of these materials relies on polymer self-assembly processes to achieve nanoscale ordering, which allows for the rapid preparation of photonic crystals from common organic chemical feedstocks. The characteristic physical properties of brush block copolymers are discussed, along with methods for their preparation. Strategies to induce self-assembly at ambient temperatures and the use of blending techniques to tune photonic properties are emphasized.

Light-triggered unfolding of single linear molecular bottlebrushes from compact globular to wormlike nano-objects in water

The photocleavage of o-nitrobenzyl moieties drives shape transitions from globular to wormlike in stimuli-responsive homografted and binary heterografted molecular bottlebrushes.

C1 polymerization: a unique tool towards polyethylene-based complex macromolecular architectures

The recent developments in organoborane initiated C1 polymerization of ylides open unique horizons towards perfectly linear polymethylenes (equivalent to PE) and PE-based complex structures. This review summarizes research on conventional and newly discovered initiators/ylides, as well as initial efforts on C3 polymerization.

(PAA-g-PS)-co-PPEGMEMA asymmetric polymer brushes: synthesis, self-assembly, and encapsulating capacity for both hydrophobic and hydrophilic agents

(PAA-g-PS)-co-PPEGMEMA asymmetric polymer brushes formed large compound micelles in aqueous media for encapsulating both hydrophobic pyrene and hydrophilic Rhodamine 6G.

Structure, function, self-assembly, and applications of bottlebrush copolymers

Bottlebrush polymers are a type of branched or graft polymer with polymeric side-chains attached to a linear backbone, and the unusual architectures of bottlebrushes provide a number of unique and potentially useful properties. These include a high entanglement molecular weight, enabling rapid self-assembly of bottlebrush block copolymers into large domain structures, the self-assembly of bottlebrush block copolymer micelles in a selective solvent even at very low dilutions, and the functionalization of bottlebrush side-chains for recognition, imaging, or drug delivery in aqueous environments. This review article focuses on recent developments in the field of bottlebrush polymers with an emphasis on applications of bottlebrush copolymers. Bottlebrush copolymers contain two (or more) different types of polymeric side-chains. Recent work has explored the diverse properties and functions of bottlebrush polymers and copolymers in solutions, films, and melts, and applications explored include photonic materials, bottlebrush films for lithographic patterning, drug delivery, and tumor detection and imaging. We provide a brief introduction to bottlebrush synthesis and physical properties and then discuss work related to: (i) bottlebrush self-assembly in melts and bulk thin films, (ii) bottlebrushes for photonics and lithography, (iii) bottlebrushes for small molecule encapsulation and delivery in solution, and (iv) bottlebrush micelles and assemblies in solution. We briefly discuss three potential areas for future research, including developing a more quantitative model of bottlebrush self-assembly in the bulk, studying the properties of bottlebrushes at interfaces, and investigating the solution assembly of bottlebrush copolymers.

Synthesis and characterization of brush-like multigraft copolymers PnBA-g-PMMA by a combination of emulsion AGET ATRP and emulsion polymerization

In this paper, poly(n-butyl acrylate)-g-poly(methyl methacrylate) multigraft copolymers were synthesized by macromonomer technique and miniemulsion copolymerization. The PMMA macromonomers were obtained by an activator generated by electron transfer atom transfer radical polymerization (AGET ATRP) in emulsion system and subsequent allylation. Then the copolymerization of different macromonomers with nBA was carried out in miniemulsion system, obtaining multigraft copolymers with high molecular weight. The latex particles and distribution of emulsion AGET ATRP and miniemulsion copolymerization were characterized using laser light scattering. The molecular weight and polydispersity indices of macromonomers and multigraft copolymers were analyzed by gel permeation chromatography, and the number-average molecular weight range is 187,600-554,800 g/mol for PnBA-g-PMMA copolymers. In addition, the structural characteristics of macromonomer and brush-like copolymers were determined by infrared spectra and (1)H nuclear magnetic resonance spectroscopy. The thermal performance of brush-like copolymers were characterized by differential scanning calorimetry and thermogravimetric analysis. Atomic force microscopy results showed that the degree of microphase separation was varying with increasing PMMA content in PnBA-g-PMMA. The dynamic rheometer analysis revealed that multigraft copolymer with PMMA content of 31.4% exhibited good elastomeric properties to function as a TPE. These multigraft copolymers show a promising low cost and environmental friendly thermoplastic elastomer.

Synthesis and characterization of graft copolymers PnBA-g-PS by miniemulsion polymerization

PnBA-g-PS by emulsion AGET ATRP and miniemulsion polymerization.

On the self-assembly of brush block copolymers in thin films

We describe a simple route to fabricate two dimensionally well-ordered, periodic nanopatterns using the self-assembly of brush block copolymers (brush BCPs). Well-developed lamellar microdomains oriented perpendicular to the substrate are achieved, without modification of the underlying substrates, and structures with feature sizes greater than 200 nm are generated due to the reduced degree of chain entanglements of brush BCPs. A near-perfect linear scaling law was found for the period, L, as a function of backbone degree of polymerization (DP) for two series of brush BCPs. The exponent increases slightly from 0.99 to 1.03 as the side chain molecular weight increases from ∼2.4 to ∼4.5 kg/mol(-1) and saturated with further increase in the side chain molecular weight due to the entropic penalty associated with the packing of the side chains. Porous templates and scaffolds from brush BCP thin films are also obtained by selective etching of one component.