Molecular structure of bottlebrush polymers in melts

Paturej, Jarosław; Sheiko, Sergei S.; Panyukov, Sergey; Rubinstein, Michael

doi:10.1126/sciadv.1601478

Cited by 218 publications

(298 citation statements)

References 71 publications

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“…However, these scaling laws are in agreement with the predictions of reptation theory in Figure 3b and Equation (3) for the comb topologies with q < Z bb . Abbasi et al [11] used the scaling analysis criteria of Sheiko and co-workers [24,25] (see details in Section 3) for this series of grafted PS to classify them into comb and bottlebrush conformations. Further reduction in η 0 as a function of M w with increasing q was achieved for combs with q > Z bb .…”

Section: Zero Shear Viscositymentioning

confidence: 99%

“…In the current paper, we investigate the transitions from comb to bottlebrush behavior; therefore, all of these variables are used for both topologies especially in the transition from comb to bottlebrush conformations. Substantial experimental [11,[29][30][31] and coarse-grained simulation works along with scaling analysis [24,25,[32][33][34][35] have been done to classify graft polymers into comb and bottlebrush classes with distinct rheological and mechanical properties. Substantial experimental [11,[29][30][31] and coarse-grained simulation works along with scaling analysis [24,25,[32][33][34][35] have been done to classify graft polymers into comb and bottlebrush classes with distinct rheological and mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

“…Figure 1 shows the correlation between these variables. [24,25] Comb topologies have a backbone and side chains with an unperturbed random Gaussian conformation, while a densely grafted bottlebrush has a stretched backbone and side chains. The differences observed between comb and bottlebrush structures were related to the Gaussian and stretched conformations of the backbone and side chains.…”

Section: Introductionmentioning

confidence: 99%

“…The differences observed between comb and bottlebrush structures were related to the Gaussian and stretched conformations of the backbone and side chains. [3,24,25,32,44] Side chains in comb polymers increase the friction of the backbone chain with neighboring molecules in the melt or solution state, which enhances the strain hardening (see below) of the polymer melt under processing conditions. The side chains of the comb topologies can easily overlap physically with each other, while densely grafted bottlebrush molecules are segregated and weakly penetrated.…”

Section: Introductionmentioning

confidence: 99%

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Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties

2019

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combined with the grafting-to method [1,10] results in comb polystyrenes (PSs) with well-entangled monodisperse backbone and side chains; however, branch points along the backbone are randomly distributed. This random distribution of branch points has no distinct effect on the rheological properties of dense comb topologies; however, it will broaden the backbone relaxation time of loose comb topologies even though the molecular weight distribution is narrow enough. [11] A controlled branching point spacing can be achieved through the coupling of living macroanions; [12] however, this method is prone to slightly high molecular weight distribution, Ð > 1.5. Synthesis of welldefined densely grafted bottlebrushes using ROMP and grafting-through method guarantees the presence of one side chain per repeating unit on the backbone. Bottlebrushes with more than one branch per backbone repeating unit can also be synthesized using ROMP and macromonomers with more bulky groups referred as wedge polymers. [13] These bottlebrushes are similar to that of the dendronized polymer with only one layer of grafting. Loosely grafted bottlebrushes with longer distance between the branching points can be achieved using ROMP technique through copolymerization of macromonomer and a diluent molecule, e.g., racemic endo,exo-norbornenyl diesters, with different ratios. However, different reactivity of macromonomer and diluent leads to a gradient of branching point spacing along the backbone, [14] where the conformations of side chains along the backbone are affected by this gradient. [15] It should be mentioned that the bottlebrushes synthesized with ROMP technique have different repeating units in the backbone than the side chains which might cause microphase separation. However this issue could be ignorable in dense bottlebrushes where the volume fraction of backbone is less than 1 wt%. In order to avoid any microphase separation, Sheiko and co-workers [16] synthesized a series of dense combs and loose bottlebrushes homo poly(n-butyl acrylates) (PBA) with similar side chains and systematically varied grafting density through copolymerization of nonfunctional n-butyl acrylates with trimethylsilyl-protected acrylates by ATRP. However, in order to achieve high degree of polymerization (DP) of backbone (entangled system) for dense bottlebrushes, they had to use slightly different backbones, i.e., poly(n-butyl methacrylate). An organometallic coordinative insertion polymerization of α-olefins results in entangled densely grafted bottlebrushes with rod-like side chains where both backbone and side chains have alkane groups. However the dispersity index of such homopolymer bottlebrushes would Comb and bottlebrush polymers present a wide range of rheological and mechanical properties that can be controlled through their molecular characteristics, such as the backbone and side chain lengths as well as the number of branches per molecule or the grafting density. This review investigates the impact of these characteristics specifically on the zero sh...

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Section: Zero Shear Viscositymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties

2019

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“…The grafting density and distribution of grafts along the backbone determine the steric interactions between side chains and in turn influence the physical properties. 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.…”

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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Methods

2019

Liquid Silicone Rubber

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Molecular structure of bottlebrush polymers in melts

Abstract: Steric repulsion between grafted side chains inhibits interpenetration of bottlebrushes, transforming them into flexible filaments.

Cited by 218 publications

References 71 publications

Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties

Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties

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

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