Ultrafast Self-Assembly of Bottlebrush Statistical Copolymers: Well-Ordered Nanostructures from One-Pot Polymerizations

We report the synthesis of a bottlebrush statistical copolymer (BSCP) architecture and its role in directing molecular packing in the bulk state. Copolymers with a statistical distribution of two chemically distinct side chains on a common polymer backbone were prepared via one-pot ring-opening metathesis polymerization (ROMP) of norbornene-capped macromonomers with similar reactivities. Kinetic studies suggest a near-random compositional profile of polystyrene (PS) and poly­(dimethyl siloxane) (PDMS) side chains along the backbone. The PS-stat-PDMS BSCPs with symmetric volume fractions rapidly assembled into lamellar microstructures when cast from solution without any further thermal or solvent annealing. The domain size is controlled by the side-chain length, ranging from below 10 nm to almost 20 nm. Furthermore, the bottlebrush statistical copolymer self-assembly yielded oriented lamellar morphologies over large areas after thermal annealing for 10 min at 200 °C without external guiding via surface or topographic patterning. Such statistical architectural control of the composition enables a simple preparation route for copolymers for potential use in the directed self-assembly of device architectures and other applications that require well-defined morphologies

Well-Defined Ambipolar Block Copolymers Containing Monophosphorescent Dye

Well-defined ambipolar block copolymers containing carbazole, oxadiazole moieties, and only one homoleptic iridium­(III) complex between the carbazole and oxadiazole blocks were successfully synthesized by sequential living anionic polymerization with controlled molecular weights (Mw), a narrow molecular weight distribution (Mw/Mn < 1.15), and a high conversion yield (98–100%). The optimum conditions for the successful controlled synthesis of an oxadiazole-containing the homopolymer of poly­(2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole) have been established by controlling the nucleophilicity strength of the carbanion. In addition, the location and concentration of the homoleptic iridium­(III) complex were controlled by linking it to 1,1-diphenylethylene, which exhibits monoaddition characteristics in the main chain of the block copolymer

Facile Synthesis of Amphiphilic Bottlebrush Block Copolymers Bearing Pyridine Pendants via Click Reaction from Protected Alkyne Side Groups

We present the facile synthetic platform for the production of amphiphilic bottlebrush block copolymers bearing pyridine pendants through combination of living anionic polymerization (LAP), ring-opening metathesis polymerization (ROMP), and copper-catalyzed azide–alkyne cycloaddition (CuAAC). ω-Norbornenyl poly­(4-((trimethylsilyl)­ethynyl)­styrene) (NBPTMSESt) with controlled molecular weights (Mn = 3–4 kDa) and low dispersity (Đ = 1.03–1.08) was synthesized by LAP and the subsequent end-capping reaction with exo-N-(n-decyl-10-phenylacrylate)-5-norbornene-2,3-dicarboximide. Well-defined bottlebrush block copolymers (Mn = 134–548 kDa, Đ = 1.04–1.14) were achieved through sequential ROMP of ω-norbornenyl polystyrene with NBPTMSESt and subsequently deprotected with the clickable alkyne group. Amphiphilic bottlebrush block copolymers were obtained by the click reaction of alkyne and azide functional pyridines in the presence of the organic-soluble catalyst/ligand system of CuBr­(PPh3)3 and N,N,N′,N″,N″-pentamethyldiethylenetriamine. These polymers exhibited the three-dimensional ordered porous films through breath-figure self-assembly

End-Capping Reaction of Living Anionic Poly(benzyl methacrylate) with a Pentafluorophenyl Ester for a Norbornenyl-ω-End Macromonomer with a Long Flexible Spacer: Advantage in the Well-Controlled Synthesis of Ultrahigh-Molecular-Weight Bottlebrush Polymers

12-(cis-5-Norbornene-exo-2,3-dicarboximido)­dodecanoate pentafluorophenyl ester (exo-NBC12-PFP) was used as a norbornene-substituted end-capping terminator of living anionic polymers. Polystyrene with a terminal 1,1-diphenylethyllithium (PSt­(DPE)−Li+), poly­(2-vinylpyridine) with a terminal 2-pyridinylethyllithium (P2VP–Li+), and poly­(benzyl methacrylate) with a terminal lithium ester enolate (PBzMA–Li+) reacted with exo-NBC12-PFP under appropriate reaction conditions to generate norbornenyl-ω-end macromonomers, NBC12-PSt, NBC12-P2VP, and NBC12-PBzMA, respectively, each with a 12-carbon spacer. To estimate the efficiency of end-capping, these macromonomers were polymerized by grafting-through ring-opening metathesis polymerization (ROMP). The end-capping reaction of PSt­(DPE)−Li+ and P2VP–Li+ suffered from side reactions resulting in low end-capping efficiencies and the generation of by-products. On the other hand, the side reactions were minimal in the end-capping reaction of PBzMA–Li+, resulting in a high end-capping efficiency of 95%. The ROMP of NBC12-PBzMA allowed the synthesis of poly­[12-(5-norbornene-exo-2,3-dicarboximido)­dodecanoylate]-graft-poly­(benzyl methacrylate)­s (PNBC12-g-PBzMAs) with a wide range of controlled molecular weights (Mn = 436–4048 kDa, Đ = 1.07–1.23)

Experimental Formulation of Photonic Crystal Properties for Hierarchically Self-Assembled POSS–Bottlebrush Block Copolymers

Rodlike “POSS–bottlebrush block copolymers” (POSSBBCPs) containing crystalline polyhedral oligomeric silsesquioxane (POSS) pendants in A block and amorphous polymeric grafts in B block were utilized to create one-dimensional (1D) photonic crystals (PCs). 3-(12-(<i>cis</i>-5-Norbornene-<i>exo</i>-2,3-dicarboximido)­dodecanoylamino)­propyl­heptaisobutyl POSS (<b>NB-A16-POSS</b>, M_A) and <i>exo</i>-5-norbornene-2-carbonyl-end poly­(benzyl methacrylate) (<b>NBPBzMA</b>, M_B) were employed in sequential ring-opening metathesis polymerization to afford poly­[3-(12-(<i>cis</i>-5-norbornene-<i>exo</i>-2,3-dicarboximido)­dodecanoylamino)­propyl­heptaisobutyl POSS]-<i>block</i>-poly­(<i>exo</i>-5-norbornene-2-carbonylate-<i>graft</i>-benzyl methacrylate)­s, <b>P­(NB-A16-POSS)-</b><i><b>b</b></i><b>-P­(NB-</b><i><b>g</b></i><b>-BzMA)</b>s, with well-modulated block compositions (<i>f</i>_A = 34, 50, and 67 wt %) and overall degrees of polymerization (DP = 323–939). The <b>P­(NB-A16-POSS)-</b><i><b>b</b></i><b>-P­(NB-</b><i><b>g</b></i><b>-BzMA)</b>s hierarchically self-assembled to form highly ordered 1D PC films with periodic lamellar arrays that can reflect visible light with particular wavelengths. Their reflectance bandwidths, reflectivities, and ranges of peak reflectance wavelnegth (λ_peak) were largely dependent on the block composition. The 1D PC films based on lamellar <b>P­(NB-A16-POSS)-</b><i><b>b</b></i><b>-P­(NB-</b><i><b>g</b></i><b>-BzMA)</b>s demonstrated the capability of formaulation of λ_peak as linear functions of initial polymerization parameter ([M]₀/[I]₀)

Molecular Design of an Interfacially Active POSS-Bottlebrush Block Copolymer for the Fabrication of Three-Dimensional Porous Films with Unimodal Pore Size Distributions through the Breath-Figure Self-Assembly

We compared the interfacial activity of two classes of POSS-bottlebrush block copolymers (POSSBBCPs) in the breath-figure (BF) self-assembly. Poly­[3-(5-norbornene-exo-2,3-dicarboximido)­propyl-heptaisobutyl POSS]-block-poly­(exo-5-norbornene-2-carbonylate-graft-benzyl methacrylate) (P1-b-P­(NB-g-BzMA)) and poly­[3-(2-(5-norbornene-exo-2,3-dicarboximido)­ethylamino)­propyl-heptaisobutyl POSS]-block-poly­(exo-5-norbornene-2-carbonylate-graft-benzyl methacrylate) (P2-b-P­(NB-g-BzMA)), which contain nonfunctionalized and secondary-amino-functionalized POSS-based blocks, respectively, were prepared by sequential ring-opening metathesis polymerization of norbornenyl monomers (P1-b-P­(NB-g-BzMA) with fP1 = 50 wt % (1–50): Mn = 213 kDa, Đ = 1.12; P2-b-P­(NB-g-BzMA)s with fP2 = 5/11/20/50 wt % (2–5/11/20/50): Mn = 2464/1043/581/268 kDa, Đ = 1.46/1.26/1.24/1.20). Of 1–50 and 2–50, only 2–50 afforded the three-dimensional porous films with unimodal pore size distributions. At high wet thickness, the efficient encapsulation of water droplets through the adsorption of water by the secondary amino groups allowed the 2–50 chains to stabilize the solvent–water interfaces, thus preventing the formation of giant pores. The interfacial activity of P2-b-P­(NB-g-BzMA) was enhanced by increasing the weight fraction of the P2 block from 5 to 50 wt %

Hydrogen Bonding-Mediated Phase Transition of Polystyrene and Polyhydroxystyrene Bottlebrush Block Copolymers with Polyethylene Glycol

A simple strategy was explored to systematically control the phase transition of an amphiphilic bottlebrush block copolymer (AmBBCP), poly­[(norbornene-graft-styrene)-block-(norbornene-graft-hydroxystyrene)], with polymeric additives, such as poly­(ethylene glycol) methyl ether (mPEG), poly­(2-vinylpyridine) (P2VP), and poly­(methyl methacrylate) (PMMA). The precursor polymers, poly­[(norbornene-graft-styrene)-block-(norbornene-graft-4-tert-butoxystyrene)], were synthesized by sequential ring-opening metathesis polymerization of ω-end-norbornyl polystyrene and poly­(4-tert-butoxystyrene). Acid hydrolysis of the tert-butyl groups in the precursor resulted in the AmBBCP with an ultrahigh molecular weight (∼2880 kDa) and relatively low dispersity (∼1.21). The disordered structures of neat AmBBCP were transformed to ordered lamellae by solvothermal annealing. AmBBCP and mPEG blended well because of H-bonding, maintaining well-ordered lamellae up to 40 wt % mPEG. The phase transition from ordered to disordered state occurred when increasing more than 50 wt %. The AmBBCP blended with P2VP and PMMA was compared. The effect of mPEG on phase transition, domain size, and refractive index and the photonic properties were determined

Large-Pore Ordered Mesoporous Turbostratic Carbon Films Prepared Using Rapid Thermal Annealing for High-Performance Micro-pseudocapacitors

Carbonization by rapid thermal annealing (RTA) of precursor films structured by a brush block copolymer-mediated self-assembly enabled the preparation of large-pore (40 nm) ordered mesoporous carbon (MPC)-based micro-supercapacitors within minutes. The large pore size of the fabricated films facilitates both rapid electrolyte diffusion for carbon-based electric double-layer capacitors and conformal deposition of V2O5 without pore blockage for pseudocapacitors. The pores were templated using bottlebrush block copolymers (BBCPs) via cooperative assembly of phenol-formaldehyde resin to produce microphase-segregated carbon precursor films on a variety of substrates. Ultrafast RTA processing (∼50 °C/s) at elevated temperatures (up to 1000 °C) then generated stable, conductive, turbostratic MPC films, resolving a significant bottleneck in rapid fabrication. MPC prepared on stainless steel at 900 °C demonstrated exceptionally high areal and volumetric capacitances of 6.3 mF/cm2 and 126 F/cm3 (at 0.8 mA/cm2 using 6 M KOH as the electrolyte), respectively, and 91% capacitance retention after 10,000 galvanostatic charge/discharge cycles. Post-RTA conformal V2O5 deposition yielded pseudocapacitors with 10-fold increase in energy density (20 μW h cm–2 μm–1) without adversely affecting the high power density (450 μW cm–2 μm–1). The use of RTA coupled with BBCP templating opens avenues for scalable, rapid fabrication of high-performance carbon-based micro-pseudocapacitors

Self-assembly of POSS–Polystyrene Bottlebrush Block Copolymers on an Angle-Robust Selective Absorber for Enhancing the Purity of Reflective Structural Color

A facile approach for improving color purity is explored by the introduction of an angle-robust selective absorber (ARSA) into bottlebrush block copolymer (BBCP)-based one-dimensional (1D) photonic crystals (PCs). The BBCPs of poly[(3-(12-(cis-5-norbornene-exo-2,3-dicarboximido)dodecanoylamino)propyl POSS)-block-(norbornene-graft-styrene)], Px (x = 1–4), with ultrahigh molecular weights (Mn ∼ 2260 kDa) and low dispersities (D̵ ∼ 1.07) are synthesized by ring-opening metathesis polymerization. The 1D PCs of the lamellar structure are fabricated by self-assembly of the BBCP with different periodicities for full color-generation (blue, green, and red). The optically tailored substrate (i.e., ARSA) is used to modulate the spectral line shape with selective absorption in the near-infrared range. Optical simulation proposes the optimized 1D PC structures on the ARSA, and it provides the reproducibility of the predictable color. The simulated structures are well matched with the experimental results, verifying the enhancement of color saturation even at various incident angles (0–70°)

Folding of Sequence-Controlled Graft Copolymers to Subdomain-Defined Single-Chain Nanoparticles

We developed a methodology, inspired by the folding of proteins, for the precision synthesis of hairy polymer nanoparticles. High-molar mass and narrowly dispersed graft copolymers were synthesized by graft-through ring opening metathesis polymerization, to incorporate a designated number of side chains and dimerizable cinnamic acid groups. Intrachain photodimerization collapsed the backbone and arrested it into a compact globular conformation, resulting in hairy nanoparticles topologically equivalent to a core cross-linked star polymer. The single-chain collapse process translates the molecular information written on the 1D graft copolymer into the 3D globular polymer nanoparticle, like protein folding. Unprecedented control over structural parameters was achieved, including the length, number, and composition of the side chains as well as cross-linking density. Different side chains formed distinct subdomains in the sterically congested nanoparticle state and further self-assembled into micellar aggregates in a selective solvent. Both experimental observations and computational simulations indicated that preorganization of the side chains in the block sequence produces subdomains which primarily follow the backbone length scale, while random sequences showed side chain-dependent scaling. Polymer nanoparticles with discrete multiple subdomains were produced by folding of the ternary block graft copolymers. Drastic differences in the self-assembly behavior of ABC- and ACB-sequenced nanoparticles indicate that the spatial organization of subdomains can be achieved by sequence control