Nonlinear rheology of model comb polymers

Kapnistos, M.; Kirkwood, Keith M.; Ramı́rez, Jorge; Vlassopoulos, D.; Leal, L. Gary

doi:10.1122/1.3191781

Cited by 38 publications

(67 citation statements)

References 55 publications

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“…[36][37][38][39][40][41][42][43][44] However, the impacts of grafting density on block polymer self-assembly have not been explored. [45][46][47][48] Elucidating these physical principles is not only of fundamental importance but should also guide material design.…”

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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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confidence: 99%

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

et al. 2017

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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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“…As for the long chain branch, it is noteworthy to mention the damping functions of comb polymers (Lee et al, 2009 andKapnistos et al, 2009). The damping functions of comb polymers are still decreasing functions of strain just as those of linear polymers although structures of comb polymers are reflected in the damping behavior.…”

Section: Classification Of Complex Fluidsmentioning

confidence: 98%

“…For this reason, one may consider applying nonlinear viscoelasticity as an alternative to the linear viscoelasticity. Nonlinear stress relaxation is a good example because it is considerably easy to connect nonlinear experiments with molecular theories such as the Doi-Edwards model and its modified versions through the damping function (Einaga et al, 1971;Osaki et al, 1982;Larson, 1985;Archer et al, 2002;Inoue et al, 2002;Lee et al, 2009;Kapnistos et al, 2009). However, the superposition in nonlinear relaxation modulus is limited to the long time period region and relaxation test usually suffers from inherent errors in the short time region because a perfect step function cannot be implemented as a strain in any experiment.…”

Section: Introductionmentioning

confidence: 98%

Effect of temporary network structure on linear and nonlinear viscoelasticity of polymer solutions

Cho

Kim

Bae

et al. 2015

Korea-Aust. Rheol. J.

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We investigated the effects of temporary network structures on linear and nonlinear viscoelasticity of polymer solutions by use of oscillatory shear (LAOS) flow. We tested two different types of polymer solutions: entanglement systems and ion complex systems. It was found that the entanglement network is difficult to show shear-thickening while network of ion complex gives rise to shear-thickening. The objectives of this paper are the test of strain-frequency superposition for various polymer solutions and to suggest a new method classifying complex fluids consisting temporary networks using LAOS data.

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Nonlinear rheology of model comb polymers

Cited by 38 publications

References 55 publications

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

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

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

Effect of temporary network structure on linear and nonlinear viscoelasticity of polymer solutions

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