Synthesis and characterization of multiarm star polybutadienes

Roovers, Jacques; Toporowski, P. M.; Martin, James P.

doi:10.1021/ma00194a064

Cited by 121 publications

(95 citation statements)

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“…The effective starlinear polymer interactions are shown to be responsible for the observed counterintuitive phenomena, via a depletionlike mechanism which explains the gel-liquid transition. Eventually, for very high molecular weights a reentrant gelation is observed and attributed to bridging flocculation induced by the long polymer chains.We used model 1,4-polybutadiene starlike entities that are virtually identical to ideal stars [11,13] with f 263 arms and arm molecular weight 42 300 g=mol, (hydrodynamic radius R st H 63 nm, gyration radius R st g 54 nm), coded as LS6, synthesized via hydrosilylation chemistry [14]. At a concentration of 2.5% weight (wt) in the athermal solvent toluene (the star overlap concentration being c 1:8%), a gel is formed, characterized by nearly frequency-independent dynamic storage (G 0 ) and loss (G 00 < G 0 ) moduli over a wide frequency range.…”

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confidence: 99%

“…We used model 1,4-polybutadiene starlike entities that are virtually identical to ideal stars [11,13] with f 263 arms and arm molecular weight 42 300 g=mol, (hydrodynamic radius R st H 63 nm, gyration radius R st g 54 nm), coded as LS6, synthesized via hydrosilylation chemistry [14]. At a concentration of 2.5% weight (wt) in the athermal solvent toluene (the star overlap concentration being c 1:8%), a gel is formed, characterized by nearly frequency-independent dynamic storage (G 0 ) and loss (G 00 < G 0 ) moduli over a wide frequency range.…”

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confidence: 99%

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Polymer-Mediated Melting in Ultrasoft Colloidal Gels

et al. 2002

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Star polymers with a high number of arms, f 263, become kinetically trapped when dispersed in an athermal solvent at concentrations above the overlapping one, forming physical gels. We show that the addition of linear chains at different concentrations and molecular weights reduces the modulus of the gel, eventually melting it. We explain this linear polymer-induced gel-liquid transition in terms of effective interactions and star depletion. In the limit of very high linear-chain molecular weight a ''reentrant gelation'' is detected and attributed to bridging flocculation, analogous to that observed in colloidal dispersions. DOI: 10.1103/PhysRevLett.89.208302 PACS numbers: 82.70.Gg, 61.20.-p, 61.25.Hq, 82.70.Dd One of the most intriguing features of colloidal dispersions is the wide range of rheological behavior they exhibit, from liquidlike to solidlike, and which depends primarily on their volume fraction [1][2][3][4][5]. This behavior is well established for hard spheres, which have received a great deal of attention; on the other hand, for soft spheres, such as hard colloids with grafted polymeric layers, it is intrinsically related to the changing thickness of the layer and thus to the strength and range of the repulsive interactions [6]. Star polymers with high functionality have emerged as a novel class of ultrasoft colloidal particles, characterized by wide ranging interactions with Yukawatype repulsions at long distances and logarithmic repulsions at short ones [7,8]. At high volume fractions, achieved via manipulation of their effective thickness in conditions of varying solvent quality, these systems exhibit a liquid-solid transition, which is of kinetic, rather than thermodynamic, origin [9][10][11]. This type of dynamic arrest is described as glasslike gelation, bearing many similarities with both colloidal glass formation (crowding of single particles) and colloidal gelation (formation of clusters) [11], and represents a manifestation of jammed colloidal particles [12]. The great challenge with such transitions is how to achieve molecular control by tuning the dynamic response. This will have a significant scientific and technological impact as it will open the route for the rational design of soft materials with desired properties in a variety of situations. Mixtures of star polymers with linear polymers are an obvious choice (as many soft matter systems occur as mixtures), which, however, has been overlooked so far.In this Letter, we demonstrate the dramatic and unexpected effects of the addition of linear chains to a star polymer gel. We show that the added polymer reduces the modulus of the gel and in the limit of high polymer molecular weight or concentration, the gel melts. Within the liquified region, the reduced star viscosity drops upon further addition of linear polymer. The effective starlinear polymer interactions are shown to be responsible for the observed counterintuitive phenomena, via a depletionlike mechanism which explains the gel-liquid transition. Eventually, for very high ...

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Polymer-Mediated Melting in Ultrasoft Colloidal Gels

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“…It is also advantageous for the large-scale synthesis of star polymers with many arms. Roovers et al, 136 Deffieux et al, 132,133 and Hadjichristidis et al 110 have reported the same subject on star polymer synthesis mentioned in introduction of this chapter. …”

Section: Densely Branched Polymers Carrying Single Branch In Every Rementioning

confidence: 62%

Precise Synthesis of Regular and Asymmetric Star Polymers and Densely Branched Polymers with Starlike Structures by Means of Living Anionic Polymerization

Hirao

Hayashi

Tokuda

et al. 2002

Polym J

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ABSTRACT:The subject of this review is to present new synthetic methodologies recently developed by us, which are applicable to both regular and asymmetric star polymers with well-defined architectures. The first methodology involves the coupling reaction of a variety of living anionic polymers of styrene, α-methylstyrene, isoprene, tert-butyl methacrylate, and ethylene oxide with novel chain-end-and in-chain-functionalized polymers with a definite number of benzyl halide moieties intentionally designed as polymeric coupling agents. In the second methodology, we propose a new concept based on iterative approach, with which star polymers can be successively and, in principle, unlimitedly synthesized by repeating the iterative reaction sequence. Finally, a convenient synthesis of densely branched polymers with starlike structures is presented by the quantitative coupling reaction of living anionic polymers with reactive benzyl halide-functionalized backbone polymers based on a grafting-onto method.KEY WORDS Star Polymer / Asymmetric Star Polymer / Living Anionic Polymerization / Iterative Methodology / Polymeric Coupling Agent / 1,1-Diphenylethylene Derivative / Star polymers are branched polymers in which more than three linear polymer chains are linked together at one end of each chain by a central core or a single branch. They have physical properties in bulk, melt, and solution quite distinct from linear analogues. For this reason, star polymers have been widely studied from both synthetic and theoretical points of view. [1][2][3][4][5][6][7][8][9] It is of course essential to use star polymers with welldefined structures for evaluating fundamental understanding regarding the effect of chain branching on such physical properties.At the present time, the most successful methodologies for the synthesis well-defined regular star polymers have been developed mainly based on coupling reactions of living anionic polymers of styrene and 1,3-dinene monomers with multifunctional chlorosilane compounds as electrophilic coupling agents. A variety of star polymers with a definite number of three to eighteen arms have been synthesized. [10][11][12][13][14][15][16][17][18][19] Furthermore, the successful syntheses of the 32-, 64-, and even 128-arm star polymers by using specially designed carbosilane dendrimers have been reported so far. 20,21 Currently, great attention has been paid to more complex asymmetric star polymers whose arms differ in molecular weight and chemical composition, since star polymers of this type are expected to exhibit interesting and unique physical performance originated from their † To whom correspondence should be addressed.branched architectures as well as heterophase structures. [22][23][24][25][26][27][28][29][30][31][32][33] Synthesis of asymmetric star polymers is generally more difficult than that of regular star polymers. In the synthesis of regular star polymers, for example, their arms can be simultaneously introduced by one reaction. On the other hand, two or more highyielding reactions...

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“…The synthesis of multiarm star polymers with 1,4-polybutadiene arms and a very high functionality (about 270) has been described in detail elsewhere [15]. Briefly, a short 1,2-polybutadiene backbone chain was hydrosilylated with HSi(CH 3 )Cl 2 yielding two coupling sites per monomer unit; the latter were substituted with 1,4-polybutadiene by adding of poly(butadienyl)lithium.…”

Section: Methodsmentioning

confidence: 99%

Structure and Dynamics of Irregular Multiarm Star Polymers

Vlassopoulos¹,

Pakula²,

Roovers³

2002

Condens. Matter Phys.

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Melt properties of highly branched star polymers consisting of a 1,2-polybutadiene core and nearly 270 arms of 1,4-polybutadiene with varying sizes have been investigated using small angle X-ray scattering (SAXS) and dynamic rheological measurements in the linear viscoelastic limit. Despite their difference in internal structure compared to the regular stars with 128 arms and spherical dendritic core, these polymers exhibit the same features: a liquid-like ordering resulting from their specific intramolecular monomer density distribution. This leads to a dual terminal viscoelastic relaxation, consisting of a fast arm relaxation and a slow structural relaxation mechanisms. Both modes conform quantitatively to the generic behaviour of multiarm star polymers, suggesting a universality of the behaviour of highly branched macromolecular objects.

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Synthesis and characterization of multiarm star polybutadienes

Cited by 121 publications

References 20 publications

Polymer-Mediated Melting in Ultrasoft Colloidal Gels

Polymer-Mediated Melting in Ultrasoft Colloidal Gels

Precise Synthesis of Regular and Asymmetric Star Polymers and Densely Branched Polymers with Starlike Structures by Means of Living Anionic Polymerization

Structure and Dynamics of Irregular Multiarm Star Polymers

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