Polymers cross-linked structure

Liquid crystal polymers Cross-linked Structures Polyblends... 

Many polymers containing boron in the main chain have been prepared but most of them have either been of low molecular weight or intractable cross-linked structures. Some interest has been shown in the tri-3-aminoborazoles, which polymerise on heating (Figure 29.15f. ... 

In previous works [18-20,23,102] water-soluble polymers such as polyacrylamide (pAM), polysodium acrylate (pAA Na), poly(acrylamide-sodium acrylate) (pAM-AA Na), poly(acrylamide-diallyethylamine-hy-drochloride) (pAM-DAEA-HCl), and poly(acrylamide-sodium acrylate-diallyethylamine-hydrochloride) (pAM-AANa-DAEA-HCl) were used in the recovery of cations and some radioactive isotopes from aqueous solutions. It was found that the floe is formed between the added polymer and ions of the solution in the flocculation process with the formation of a crosslinked structure. The formed cross-linked structure is characterized by [103-105] ... 

A new polymer type which emerged as important materials for circuit hoards are polycyanurates. The simplest monomer is the dicyanate ester of hisphenol A. When polymerized, it forms three-dimensional, densly cross-linked structures through three-way cyanuric acid (2,4,6-triazinetriol) ... 

Our laboratory has planned the theoretical approach to those systems and their technological applications from the point of view that as electrochemical systems they have to follow electrochemical theories, but as polymeric materials they have to respond to the models of polymer science. The solution has been to integrate electrochemistry and polymer science.178 This task required the inclusion of the electrode structure inside electrochemical models. Apparently the task would be easier if regular and crystallographic structures were involved, but most of the electrogenerated conducting polymers have an amorphous and cross-linked structure. 

Figure 39 The enantioselective polymer-supported catalysts (61) of chiral oxazaborolidinone with cross-linking structures for use in the Diels-Alder reaction of methacrolein with cyclopentadiene. (Adapted from ref. 85.)...

In the energy domain, new and efficient uses in gas lines, electric cable ducts and the like, will promote surface stabilization and endurance as well as complex stress capability of various extruded or cast systems. Such reactants as acetylene terminated polymers have yielded cross-linked cured, networks of exceptional density and durability. A diimide dianhydride combined with (3) ethynylaniline yields an acetylene terminated tetraimide. On further polymerization at 250°C, the cross-linked structure derived can be used continuously at about 230°C. When this is combined with polymer carbon fibers or filaments, an exceedingly refractory and tough binder is produced. 

The base resin contains a styrene-divinylbenzene polymer, DVB. If styrene alone were used, the long chains it formed would disperse in organic solvents. The divinylbenzene provides cross-linking between the chains. When the cross-linked structure is immersed in an organic solvent, dispersion takes place only to the point at which the osmotic force of solvation is balanced by the restraining force of the stretched polymer structure. 

To further suppress the insertion of dyes into the channels from the substrate side, the channels can be sealed on one side by adsorption of a polymer onto the substrate [48,49]. Alternatively, stopcocks can be functionalised specifically with electroreactive constituents like ethynylic [50] vinylic [51], or pyrrolic groups [52,53]. The substrate serves as electrode under the influence of an electrochemical potential and only the adjacent heads of the stopcocks react to form a covalently cross-linked structure. The stopcocks are then removed from the other side of the crystals to unblock the channels for the dye insertion. 

Figure 7.14 (a) Chemical structure of a phosphine-platinum mechanoresponsive MSP prepared by Paulusse et al. (2006, 2007) and (b) schematic representation of gels prepared by a similar polymer cross-linked with Ir or Rh salts. 

As discussed earlier, hydrogels can be prepared by cross-linking water-soluble polymers. When immersed in water, such materials absorb water and swell, but they cannot dissolve because of the constraints imposed by the cross-linked structure. The volume expansion is limited by the degree of cross-linking. The minimum number of cross-links required to form an insoluble matrix is approximately 1.5 per chain, and this yields a system with the maximum expansion possible without separation of the chains into a true solution. Thus, a hydrogel may be more than 95% water, yet it has structure and, in that sense, has much in common with living soft tissues. 

Polymers are more fundamentally categorized as linear, branched, and cross-linked structures. Linear polymers (e.g., polyesters) are constructed from strictly... 

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