ABA Triblock Brush Polymers: Synthesis, Self-Assembly, Conductivity, and Rheological Properties

Bates, Christopher M.; Chang, Alice B.; Momčilović, Nebojša; Jones, Simon C.; Grubbs, Robert H.

doi:10.1021/acs.macromol.5b00880

Cited by 171 publications

(214 citation statements)

References 37 publications

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“…ABC and ABA′ brush triblock polymers containing grafted poly( D,L -lactide) (PLA, A block), polystyrene (PS, B block), and poly(ethylene oxide) (PEO, C block) side chains were synthesized by ring-opening metathesis polymerization (ROMP) (20)(21)(22). The living nature and synthetic utility of ROMP enable the formation of welldefined block polymers with precisely controlled molar mass, narrow molar mass dispersity, and diverse pendant functionalities.…”

Section: Resultsmentioning

confidence: 99%

Manipulating the ABCs of self-assembly via low-χ block polymer design

Chang

Bates

Lee

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Block polymer self-assembly typically translates molecular chain connectivity into mesoscale structure by exploiting incompatible blocks with large interaction parameters (χ ij ). In this article, we demonstrate that the converse approach, encoding low-χ interactions in ABC bottlebrush triblock terpolymers (χ AC ≲ 0), promotes organization into a unique mixed-domain lamellar morphology, which we designate LAM P . Transmission electron microscopy indicates that LAM P exhibits ACBC domain connectivity, in contrast to conventional three-domain lamellae (LAM 3 ) with ABCB periods. Complementary small-angle X-ray scattering experiments reveal a strongly decreasing domain spacing with increasing total molar mass. Self-consistent field theory reinforces these observations and predicts that LAM P is thermodynamically stable below a critical χ AC , above which LAM 3 emerges. Both experiments and theory expose close analogies to ABA′ triblock copolymer phase behavior, collectively suggesting that low-χ interactions between chemically similar or distinct blocks intimately influence self-assembly. These conclusions provide fresh opportunities for block polymer design with potential consequences spanning all self-assembling soft materials.block polymer | self-assembly | polymer nanostructure | domain spacing | LAM P B lock polymers are a diverse class of soft materials capable of self-assembling into complex periodic nanostructures. Synthetic command over composition, dispersity, sequence, and molecular architecture enables control over the mesoscopic order and macroscopic thermal, mechanical, rheological, and transport properties (1-4). The phase behavior of "simple" linear AB diblock copolymers is universally parameterized by the segregation strength χ AB N and relative volume fraction f, where χ AB represents the effective Flory-Huggins binary interaction parameter and N is the total volume-averaged degree of polymerization. Mixing behavior, captured through the mean-field concept of χ AB , is central to block polymer self-assembly: the competing demands of minimizing interfacial energy and maximizing configurational entropy only favor microphase separation when A-B interactions are repulsive (χ AB > 0) (5, 6). Extension to higher-order multiblock polymers introduces additional interaction parameters (χ ij ) that impact self-assembly and properties (7). For example, introducing a mutually incompatible C block (χ AC > 0, χ BC > 0) generates a host of new morphologies dictated by the chain connectivity (ABC, ACB, or BAC) and intrinsic χ ij -values (8, 9). In this rich phase space, designing multiblock polymers with a combination of miscible and immiscible blocks can also access new structures and impart useful functions (10, 11). Perhaps the best-known examples of such systems are linear ABA′ triblock copolymers (χ AB > 0, χ AA′ ≈ 0): their high-value industrial applications as thermoplastic elastomers are entirely enabled by A/A′ mixing and chain connectivity, which together create physically cross-linked materials with ex...

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Section: Resultsmentioning

confidence: 99%

Manipulating the ABCs of self-assembly via low-χ block polymer design

Chang

Bates

Lee

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…We envisage that the determined scaling relationships for various grafting density series could be exploited to guide material design. 63 and PLA 23 were prepared according to previously reported precedures. Norbornene diluents DME 64 and DBE 65 were prepared by Diels-Alder reactions according to previously reported procedures.…”

Section: Discussionmentioning

confidence: 99%

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

et al. 2017

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Grafting density is an important structural parameter that exerts significant influences over the physical properties of architecturally complex polymers. In this report, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization. ω-Norbornenyl poly(d,l-lactide) and polystyrene macromonomers were copolymerized with discrete comonomers in different feed ratios, enabling precise control over both the grafting density and molecular weight. Small-angle X-ray scattering experiments demonstrate that these graft block polymers self-assemble into long-range-ordered lamellar structures. For 17 series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ∼ N bb α) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, not segregation effects. A model is proposed in which the characteristic ratio (C ∞), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ∼ N bb f(z). The scaling behavior disclosed herein provides valuable insights into conformational changes with grafting density, thus introducing opportunities for block polymer and material design.

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“…Graft polymers display many unique properties compared to their linear analogues, such as extended chain conformations, [5][6][7][8] increased entanglement molecular weights, [9][10][11][12] and architecturedependent rheological behavior. [13][14][15][16] Recent studies have harnessed these properties in a wide variety of applications in photonics, [17][18][19] drug delivery, [20][21][22] transport, [23][24] and thermoplastics. [25][26] Continued progress in synthetic command over polymer architecture enables further studies of structure-property relationships and inspires new potential applications.…”

Section: Introductionmentioning

confidence: 99%

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

et al. 2017

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Grafting density and graft distribution impact the chain dimensions and physical properties of polymers. However, achieving precise control over these structural parameters presents long-standing synthetic challenges. In this report, we introduce a versatile strategy to synthesize polymers with tailored architectures via grafting-through ring-opening metathesis polymerization (ROMP). One-pot copolymerization of an ω-norbornenyl macromonomer and a discrete norbornenyl co-monomer (diluent) provides opportunities to control the backbone sequence and therefore the side chain distribution. Toward sequence control, the homopolymerization kinetics of 23 diluents were studied, representing diverse variations in the stereochemistry, anchor groups, and substituents. These modifications tuned the homopolymerization rate constants over two orders of magnitude (0.36 M −1 s −1 < khomo < 82 M −1 s −1 ). Rate trends were identified and elucidated by complementary mechanistic and density functional theory (DFT) studies. Building on this foundation, complex architectures were achieved through copolymerizations of selected diluents with a poly(D,L-lactide) (PLA), polydimethylsiloxane (PDMS), or polystyrene (PS) macromonomer. The cross-propagation rate constants were obtained by non-linear least squares fitting of the instantaneous co-monomer concentrations according to the Mayo-Lewis terminal model. Indepth kinetic analyses indicate a wide range of accessible macromonomer/diluent reactivity ratios (0.08 < r1/r2 < 20), corresponding to blocky, gradient, or random backbone sequences. We further demonstrated the versatility of this copolymerization approach by synthesizing AB graft diblock polymers with tapered, uniform, and inverse-tapered molecular "shapes." Small-angle X-ray scattering analysis of the self-assembled structures illustrates effects of the graft distribution on the domain spacing and backbone conformation. Collectively, the insights provided herein into the ROMP mechanism, monomer design, and homo-and copolymerization rate trends offer a general strategy for the design and synthesis of graft polymers with arbitrary architectures. Controlled copolymerization therefore expands the parameter space for molecular and materials design.

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ABA Triblock Brush Polymers: Synthesis, Self-Assembly, Conductivity, and Rheological Properties

Cited by 171 publications

References 37 publications

Manipulating the ABCs of self-assembly via low-χ block polymer design

Manipulating the ABCs of self-assembly via low-χ block polymer design

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

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