Synthesis of well‐defined dendritic hyperbranched polymers by iterative methodologies using living/controlled polymerizations

Hirao, Akira; Sugiyama, Kenji; Matsuo, Akira; Tsunoda, Yuji; Watanabe, Takumi

doi:10.1002/pi.2361

Cited by 34 publications

(26 citation statements)

References 62 publications

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“…double that of the main target product (see also Refs. [32][33][34][35][36]). Whereas these side-products have an influence on the linear viscoelasticity at very long times [19], at this small amount they do not affect the terminal response of the target dendritic molecules.…”

Section: Ii1 Cayley-tree Polymersmentioning

confidence: 99%

“…Characterization of G3 and G4 can be found in Ref. [19] and [35,36]. Here we note that we performed size exclusion chromatography in fresh and used (after first stretching experiment) samples G4.…”

Section: Ii1 Cayley-tree Polymersmentioning

confidence: 99%

“…These dendritically branched macromolecules were synthesized anionically by Hirao and co-workers [32][33][34][35][36] using benzyl bromide moieties as coupling agents. Earlier rheological investigations were discussed by van Ruymbeke et al [19].…”

Section: Ii1 Cayley-tree Polymersmentioning

confidence: 99%

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Stress growth and relaxation of dendritically branched macromolecules in shear and uniaxial extension

Huang¹,

Costanzo²,

Das³

et al. 2017

Journal of Rheology

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We present unique nonlinear rheological data of well-defined symmetric Cayley-tree poly(methyl methacrylates) in shear and uniaxial extension. Earlier work has shown that their linear viscoelasticity is governed by the hierarchical relaxation of different generations, whereas the segments between branch points are responsible for their substantial strain hardening as compared to linear homopolymers of the same total molar mass at the same value of imposed stretch rate. Here, we extend that work in order to obtain further experimental evidence that will help understanding the molecular origin of the remarkable properties of these highly branched macromolecules. In particular, we address three questions pertinent to the specific molecular structure: (i) is steady state attainable during uniaxial extension? (ii) what is the respective transient response in simple shear? and (iii) how does stress relax upon cessation of extension or shear? To accomplish our goal we utilize state-of-the-art instrumentation, i.e., filament stretching rheometry (FSR) and cone-partitioned plate (CPP) shear rheometry for polymers with 3 and 4 generations, and complement it with state-of-the-art modeling predictions using the Branch-on-Branch (BoB) algorithm. The data indicates that the extensional viscosity reaches a steady state value, whose dependence on extension rate is identical to that of entangled linear and other branched polymer melts. Nonlinear shear is characterized by transient stress overshoots and the validity of the Cox-Merz rule. Remarkably, nonlinear stress relaxation is much broader and slower in extension compared to shear. It is also slower at higher generation, and rate-independent for rates below the Rouse rate of the outer segment. For extension, the relaxation time is longer than that of the linear stress relaxation, suggesting a strong 'elastic memory' of the material. These results are 2 described by BoB semi-quantitatively, both in linear and nonlinear shear and extensional regimes. Given the fact that the segments between branch points are less than 3 entanglements long, this is a very promising outcome that gives confidence in using BoB for understanding the key features. Moreover, the response of the segments between generations controls the rheology of the Cayley trees. Their substantial stretching in uniaxial extension appears responsible for strain hardening, whereas coupling of stretches of different parts of the polymer appears to be the origin of the slower subsequent relaxation of extensional stress. Concerning the latter effect, for which predictions are not available, it is hoped that the present experimental findings and proposed framework of analysis will motivate further developments in the direction of molecular constitutive models for branched and hyperbranched polymers.

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Section: Ii1 Cayley-tree Polymersmentioning

confidence: 99%

Section: Ii1 Cayley-tree Polymersmentioning

confidence: 99%

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Stress growth and relaxation of dendritically branched macromolecules in shear and uniaxial extension

Huang¹,

Costanzo²,

Das³

et al. 2017

Journal of Rheology

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“…Dendrimer-like star polymers [Scheme 1(b)], on the other hand, have a smaller but well-defined number of coupling sites strictly located at the chain ends of the previous generation, and are thus the dendrigraft polymers closest to dendrimers from a structural viewpoint [10]. Since the branching multiplicity of the chain ends (number of branching points) is relatively low (typically 2-4) in dendrimer-like polymers, the rate of molecular weight increase is also lower for these systems than for arborescent macromolecules.…”

Section: Introductionmentioning

confidence: 99%

Phase-Segregated Dendrigraft Copolymer Architectures

Cadena

Gauthier

2010

Polymers

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Dendrigraft polymers have a multi-level branched architecture resulting from the covalent assembly of macromolecular building blocks. Most of these materials are obtained in divergent (core-first) synthetic procedures whereby the molecule grows outwards in successive grafting reactions or generations. Two main types of dendrigraft polymers can be identified depending on the distribution of reactive sites over the grafting substrate: Arborescent polymers have a large and variable number of more or less uniformly distributed sites, while dendrimer-like star polymers have a lower but well-defined number of grafting sites strictly located at the ends of the substrate chains. An overview of the synthesis and the characterization of dendrigraft copolymers with phase-segregated morphologies is provided in this review for both dendrigraft polymer families. The tethering of side-chains with a different composition onto branched substrates confers unusual physical properties to these copolymers, which are highlighted through selected examples.

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“…Several reviews of DSPs have been published. [1][2][3][4][5][6][7] Thus far, DSPs have been synthesized by either stepwise iterative 'core-first' divergent or 'arm-first' convergent methodologies using living polymers as building blocks that are linked between the junctions. In the 'core-first' divergent methodology, [8][9][10][11][12][13][14][15][16] the synthesis initiates growth at a multifunctionalized initiator and continues outward by iterating the same or a similar synthetic sequence.…”

Section: Introductionmentioning

confidence: 99%

Dendrimer-like star-branched polymers: novel structurally well-defined hyperbranched polymers

Hirao

Yoo

2010

Polym J

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The precise synthesis of dendrimer-like star-branched polymers (DSPs), a novel class of structurally well-defined hyperbranched polymers, is described. The synthesis uses stepwise iterative methodologies based on the 'arm-first' divergent approach. The first methodology involves two reaction steps: (1) a linking reaction of an a-multifunctionalized living polymer(s) either with a core(s) substituted plural number of benzyl bromide (BnBr) functions or a chain-end-(BnBr) n -functionalized polymer(s) attached to the repeating unit and (2) a transformation reaction to the BnBr function that is used as the next reaction site. The two steps are repeated to construct high-molecular-weight (1.94Â10 6 g mol À1 , M w /M n ¼1.02) and high-generation (seventh generation) DSPs. The second methodology is the same as the first except for the use of a functionalized living AB diblock copolymer instead of the a-multifunctionalized living polymer(s). With this methodology, a higher molecular weight (1.43Â10 7 g mol À1 , M w /M n ¼1.05) DSP was successfully synthesized, although the number of branch segments was not exactly, rather on average, defined by the living anionic polymerization of the B segment. The resulting DSPs were characterized by right angle laser light scattering (RALLS), small-angle X-ray scattering and viscosity measurements to obtain the hydrodynamic radii, radii of gyration, intrinsic viscosity values and g' values (branching factors). The relationship among such values that reveals the sizes, volumes, shapes, and generation and branched architecture is discussed. To visualize the synthesized DSPs, an atomic force microscopy measurement was attempted.

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Synthesis of well‐defined dendritic hyperbranched polymers by iterative methodologies using living/controlled polymerizations

Cited by 34 publications

References 62 publications

Stress growth and relaxation of dendritically branched macromolecules in shear and uniaxial extension

Stress growth and relaxation of dendritically branched macromolecules in shear and uniaxial extension

Phase-Segregated Dendrigraft Copolymer Architectures

Dendrimer-like star-branched polymers: novel structurally well-defined hyperbranched polymers

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