Chemically cross-linked polymers

Diffusional inhomogeneity of probe amino acid in chemically cross-linked polymer gels... 

Coram et al. [6] have described the polymer support as a soluble macromolecule or a micellar aggregate that wraps the metal nanoparticle in solution, thus preventing metal sintering and precipitation. It can also be a resin, that is an insoluble material consisting in a bundle of physically and/or chemically cross-linked polymer chains in which the metal nanoparticles are embedded (Figure 11.2). Thus, soluble cross-linked polymers ( microgels ) that can stabilize metal nanoparticles can be prepared in addition, metal colloids protected by soluble linear polymers have been grafted onto insoluble resin supports to yield insoluble catalysts. This chapter is devoted mainly to metal nanoparticles on insoluble resin supports [8]. 

Hydrogels are physically or chemically cross-linked polymer networks swollen with large amounts of water. Due to their crosslinked nature, these gels do not dissolve in aqueous media but contain an enormous amount of solvated water molecules within the entangled polymer chain matrix. Hydrogel properties are reviewed elsewhere in this book. This chapter is dedicated to a unique hydrogel family that responds to... 

A nanogel is a nanosized hydrogel made of physically or chemically cross-linked polymers that are water-soluble. A nanogel that is composed of responsive polymers may change volume depending on the external environment [23]. 

The understanding of these physically cross-linked materials stem from the theory of rubber elasticity, which is based on a chemically cross-linked polymer, and it is to this simple idealized model that we confine attention. 

The term nanogel or microgel usually defines aqueous dispersions of hydrogel particles or colloidal networks formed by physically or chemically cross-linked polymer chains of nano-or microscale size. 

FIGURE 5.2.3 Classification of soft shape-memory materials from the viewpoint of nanoaivhitectonics. (a-c) Structures and (d) molecular mechanism, (a) Chemically cross-linked polymer network, (b) supramolecular network with clay nanosheets [29], and (c) inorganic/polymer composite network system, and their shape-memory profiles [30]. (d) The nanoscale molecular mechanism for one-way and two-way SME of a cross-linked semicrystalline polymer system. 

Figure 2.1 Schematic diagram of the two main classes of hydrogels produced by chemically cross-linked polymers (a) and (macro) molecules forming noncovalent structures (b).

Magnetic field sensitive gels are chemically cross-linked polymer networks swollen by a ferrofluid (Berkovski and Bashtovoy, 1996 Nakano and Koyama, 1997 Rosenweig, 1985). A ferrofluid or a magnetic fluid is a colloidal dispersion of monodomain magnetic particles with a typical size of about 10 nm. 

Another original approach for fabrication of nanocomposite aerogels based on CNTs and chemically cross-linked polymers was described by Zou, Liu, and Karakoti (2010). The authors first disperse MWNTs by poly(3-hexylthiophene)-b-poly(3-(trimethoxysilyl)propyl methacrylate) (P3HT-PTMSPMA) due to the n-n interaction between nanotubes and P3HT, form a physical gel and, then, cross-link the polymer layer by hydrolysis and condensation of PTMSPMA blocks (Figure 8.3). 

For chemically cross-linked polymers, ex/sm 1. and the mobiUty of a chemically cross-linked segment Fx < Fm, so that Fx/Fm 1, and the equation simplifies to... 

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