On the nature of crosslinks in thermoreversible gels

Nijenhuis, K. te

doi:10.1007/s00289-006-0610-7

Cited by 105 publications

(142 citation statements)

References 54 publications

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“…We have analyzed this network with the Flory-Stockmayer theory for tetrafunctional crosslinking of monodisperse high molecular weight polymers, extended by one of the authors for cross-links of any functionality and for polydisperse polymers. [74][75][76][77][78][79][80][81] Physical networks are in general far from ideal ( Figure 7). 82 Many polymer molecules are present which are not bound to the network (sol fraction w s ).…”

Section: Discussionmentioning

confidence: 99%

“…[74][75][76][77][78][79][80][81] Physical networks are in general far from ideal ( Figure 7). 82 Many polymer molecules are present which are not bound to the network (sol fraction w s ). Moreover many polymer molecules, or small parts of them, form dangling or free ends (fraction w f ) which also do not contribute to the rubber shear modulus G e .…”

Section: Discussionmentioning

confidence: 99%

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Unidirectional Dimerization and Stacking of Ureidopyrimidinone End Groups in Polycaprolactone Supramolecular Polymers

et al. 2007

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The effect of stacking of end groups on the rheological behavior of supramolecular polymer melts is reported. Oscillatory shear experiments in the transition zone from the pseudo rubber plateau to the flow region of telechelic polycaprolactones (PCLs) with ureidopyrimidinone (UPy) end groups directly attached to PCL can be fitted with a single Maxwell element. This demonstrates that dimerization of the UPy groups is unidirectional and that reversible chain scission is faster than reptation. If the UPy groups are connected to the polymer via a urethane linker, a low-frequency plateau in G′ is observed. This is ascribed to the formation of a network of stacked UPy dimers, aided by urethane hydrogen bonding. Below their melting point, these stacks form long fibers in the urethane linked supramolecular poly(methyl caprolactone), which were observed with atomic force microscopy (AFM). Steric hindrance interferes with stacking, since the plateau in G′ is lower in a urethane linked polymer with bulky adamantyl-UPy end groups.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Unidirectional Dimerization and Stacking of Ureidopyrimidinone End Groups in Polycaprolactone Supramolecular Polymers

et al. 2007

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“…Gelatin aqueous solutions have long attracted the interest of chemists, physicists, and food scientists because of not only its wide range of applications, such as food, cosmetics, photography, pharmacology, and glues, but also its familiarity as a model system of sol-gel transition. 75 Pioneering works on the structure analysis of gelatin aqueous systems by dynamic light scattering (DLS) were carried out in 1980s in gel state by Hwang and Cummins 76 and in sol state by Amis and co-workers. 77 The presence of collective diffusion mode was reported, and the presence of strong influence of the static component in the scattered intensity was discussed.…”

Section: Inhomogeneities In Thermoreversible Physical Gelsmentioning

confidence: 99%

Universality and Specificity of Polymer Gels Viewed by Scattering Methods

Shibayama¹

2006

Bulletin of the Chemical Society of Japan

106

112

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Concentration fluctuations in polymer gels are composed of dynamic thermal fluctuations and frozen inhomogeneities. Particularly, the latter is a characteristic of gels and is due to cross-linking. The frozen inhomogeneities manifest unique properties in polymer gels. Speckle patterns are commonly observed in gels. The time-correlation function of the scattering intensity entails a power-law behavior at the sol-gel transition. The appearance of speckle patterns is related to the nonergodicity of gels, and the power-law behavior corresponds to the self-similarity of clusters at the gelation threshold. In this review, it will be demonstrated that light scattering is one of the most powerful tools for structure characterization of polymer gels. Then, the universality and specificity of polymer gels will be examined for various types of gels, including physical gels, composite gels, and gelators.

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“…to control their rheological properties. [75][76][77][78] A microbial polysaccharide, xanthan, is one of such biopolymers with versatile properties in aqueous media and used in many areas of technology.…”

Section: Thermally-denatured Double-helical Polysaccharidementioning

confidence: 99%

Macromolecular Assemblies in Solution: Characterization by Light Scattering

Sato

Matsuda

2009

Polym. J.

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This review article demonstrates that the light scattering technique provides important structural information of the following macromolecular assemblies, polymer living anions in a non-polar solvent, amphiphilic telechelic polymer and block copolymers in aqueous solution, and a thermally denatured double-helical polysaccharide aggregated during renaturation. To get accurate information from light scattering data, however, we have to analyze the data using proper theoretical tools, which are briefly explained in this article. The structural information of these macromolecular assemblies assists us in understanding, e.g., the kinetics of living anionic polymerization and gelation. 1 There are many types of architecture of macromolecular assemblies (cf. Figure 1). For associating polymers with a single attractive moiety per chain (e.g., diblock copolymers, polymer living anions, water-soluble polymers hydrophobically modified at one end), the architecture may be spherical (star-like), cylindrical, bilayer or vesiclar.2-7 On the other hand, if the chain possesses a number of attractive moieties, its assembly may be a uni-core or multicore flower micelle. [8][9][10][11][12][13] Multi-stranded helical polymers may form assemblies of their unique architecture by the hydrogenbonding.14 The macromolecular assemblies formed by associating polymers in solution can be characterized in terms of the architecture, the size (i.e., the radius of gyration, hydrodynamic radius, or intrinsic viscosity), the average and distribution of the aggregation number, and inter-assembly interaction. However, the determination of these characteristics is not necessarily an easy task in comparison with molecularly dispersed polymers.The difficulty comes from (1) the concentration dependence of the degree of aggregation, (2) the variety and complexity of the architecture, and (3) the dispersity in the assembly structure in the case of open association systems. 15 Because of (1), the standard procedure of infinite dilution and also size exclusion chromatography does not necessarily provide right information of the assemblies at a given finite concentration. To make proper characterization, we have to take into account the association-dissociation equilibrium and inter-assembly interaction of associating polymers in solution of the finite concentration. To overcome the difficulties (2) and (3), we have to formulate characteristic parameters using models suitable for each architectures considering the dispersity effect if necessary.The present article reviews recent light scattering studies on various macromolecular assemblies in dilute solution. Light scattering is one of the most suitable techniques to characterize macromolecular assemblies in solution. Its measurements are made on assemblies in solution without any perturbations, and nanometer to sub-micrometer structures can be investigated. However, analyses of light scattering data are accompanied with the above mentioned difficulties. In what follows, we will explain the method for each sy...

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On the nature of crosslinks in thermoreversible gels

Cited by 105 publications

References 54 publications

Unidirectional Dimerization and Stacking of Ureidopyrimidinone End Groups in Polycaprolactone Supramolecular Polymers

Unidirectional Dimerization and Stacking of Ureidopyrimidinone End Groups in Polycaprolactone Supramolecular Polymers

Universality and Specificity of Polymer Gels Viewed by Scattering Methods

Macromolecular Assemblies in Solution: Characterization by Light Scattering

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