Linear rheology and structure of molecular bottlebrushes with short side chains

López‐Barrón, Carlos R.; Brant, Patrick; Eberle, Aaron P. R.; Crowther, Donna J.

doi:10.1122/1.4918977

Cited by 74 publications

(101 citation statements)

References 44 publications

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“…The increase in both d 1 and side chain mobility is also reflected as an increase in free volume, which also explains the decrease in T g , as discussed elsewhere . To quantify the free volume, we use the fractional free volume, defined as

f = \frac{v_{f}}{v_{o} + v_{f}},

where v o and v f are the occupied and free specific volumes, respectively.…”

Section: Results and Discusionmentioning

confidence: 99%

“…Despite the growing interest in molecular bottlebrushes, only a few previous studies focused on the viscoelastic response of molecular bottlebrushes as a function of their side chain and backbone lengths . The linear viscoelastic (LVE) properties of polymers with bottlebrush architecture are dominated by the ratio between the side chain length and the stiffness of the backbone.…”

Section: Introductionmentioning

confidence: 99%

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Dynamic Fragility of α‐Olefin Molecular Bottlebrushes

López‐Barrón

Hagadorn

2019

J Polym Sci B Polym Phys

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The glass transition temperature, dynamic fragilities, and flow activation energy of a series of well-entangled poly(α-olefin) (PαO) molecular bottlebrushes were measured as a function of side chain length (N sc ). The PαO bottlebrushes studied here have side chain lengths, N sc , ranging from 4 (poly(1-hexene)) to 10 (poly (1-dodecene). A linear polyolefin (polypropylene), with Nsc = 1, was included in this study as a reference. The observed glassy dynamics behavior in the PαO bottlebrushes is opposite to that observed in linear polymers, namely, the glass transition temperature, the dynamic fragility, and the activation energy of structural relaxation are decreasing functions of the backbone rigidity. This anomalous behavior is due to a decrease in correlation between adjacent backbones, which is directly related to their cooperativity in the α-relaxation, as N sc and the concomitant distance between backbones increase. This change in conformation is also manifested as an increase in free volume and the consequent decrease in monomeric friction coefficient.

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f = \frac{v_{f}}{v_{o} + v_{f}},

where v o and v f are the occupied and free specific volumes, respectively.…”

Section: Results and Discusionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dynamic Fragility of α‐Olefin Molecular Bottlebrushes

López‐Barrón

Hagadorn

2019

J Polym Sci B Polym Phys

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“…Besides critical gels, there are other viscoelastic materials with several decades of powerlaw relaxation. For example, powerlaw relaxation behavior was found for gluten dough, for bottlebrush polymers, and for branched polyethylene …”

Section: Discussionmentioning

confidence: 99%

The Solidification Rheology of Amorphous Polymers − Vitrification as Compared to Gelation

Winter

2017

Macromolecular Symposia

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The liquid‐to‐solid transition of polymeric materials results from the growth of a heterogeneous, percolating internal structure. The increased connectivity reduces the mobility of internal constituents and dominates the macroscopic rheological properties, which often appear to be very similar for gelation and vitrification. An example near the liquid‐to‐solid transition is the diverging shear viscosity, which is accompanied by high elasticity and a diverging relaxation time (critical slow down). Gelation and vitrification are hard to distinguish in this way. A distinctive difference, however, was found in the distribution of relaxation modes. Short relaxation modes dominate gelation since most internal constituents maintain their high mobility while, in comparison, the percolating structure is too weak to significantly contribute to the macroscopic behavior. The opposite is found for vitrification, which originates from large, cooperatively‐moving regions which finally connect into a percolating structure at the glass transition. As a consequence, the long relaxation modes dominate the approach of the glass transition. Surprisingly, the relaxation time spectrum adopts the same format for both phenomena near the transition, except that the relaxation exponent, n, is negative for gelation and positive for vitrification. Mathematically, one is the inverse of the other. The spectrum is cut off by the diverging longest relaxation time. Examples will be shown for these phenomena.

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“…Several studies investigated the zero shear viscosity η 0 as a function of total molecular weight for different series of loose and dense bottlebrushes with either short chain branches (SCB) [13,18,19,24,[29][30][31]57] or long chain branches (LCB). [11,30] Within these bottlebrush series, two characteristics out of n sc , n g , and n bb are fixed and one of them is varied in the series.…”

Section: Zero Shear Viscositymentioning

confidence: 99%

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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Linear rheology and structure of molecular bottlebrushes with short side chains

Cited by 74 publications

References 44 publications

Dynamic Fragility of α‐Olefin Molecular Bottlebrushes

Dynamic Fragility of α‐Olefin Molecular Bottlebrushes

The Solidification Rheology of Amorphous Polymers − Vitrification as Compared to Gelation

Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties

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