Covalent composition

Wang, Q., Hou, R., Cheng, Y., Fu, J., 2012. Super-tough double-network hydrogels reinforced by covalently compositing with silica-nanoparticles. Soft Matter 8, 6048—6056. 

Information theory has been shown to provide a novel and attractive perspective on the entropic origins of the chemical bond. It also offers a complementary outlook on the transformation of the electronic information content in the elementary chemical reactions. In this short overview, we have first introduced the key IT concepts and techniques to be used in such a complementary analysis of electron distributions in molecular systems. They have been subsequently applied to explore the bonding pattern in typical molecules in terms of the information distribution, the bond localization/multiphcity, and its ionic/covalent composition. The use of the information densities as local probes of electronic distributions in molecules has been advocated and the importance of the nonadditive entropy/information measures in extracting subtle changes due to the bond formation has been stressed. The use of the CG density, of the nonadditive Fisher information (electronic kinetic energy) in the AO resolution, as an efficient localization probe of the direct chemical bonds has been validated. 

Lithium hydride reacts vigorously with siUcates above 180°C. Therefore, glass, quart2, and porcelain containers cannot be used in preparative processes. That only traces dissolve in polar solvents such as ether reflects its significant (60—75%) covalent bond character. It is completely soluble in, and forms eutectic melting compositions with, a number of fused salts. 

The addition—reaction product of bisphenol A [80-05-07] and glycidyl methacrylate [106-91-2] is a compromise between epoxy and methacrylate resins (245). This BSI—GMA resin polymerizes through a free-radical induced covalent bonding of methacrylate rather than the epoxide reaction of epoxy resins (246). Mineral fillers coated with a silane coupling agent, which bond the powdered inorganic fillers chemically to the resin matrix, are incorporated into BSI—GMA monomer diluted with other methacrylate monomers to make it less viscous (245). A second monomer commonly used to make composites is urethane dimethacrylate [69766-88-7]. 

Superdex is a composite media of agarose and dextran. The base particle is formed of cross-linked agarose to which dextran is then covalently attached. The resulting family of Superdex-based gels has been constructed to provide... 

Chemical compounds that contain methylol groups (-CH2 OH) form stable, covalent bonds with cellulose fibers. Those compounds are well known and widely used in textile chemistry. Hydrogen bonds with cellulose can be formed in this reaction as well. The treatment of cellulose with methylolmelamine compounds before forming cellulose unsaturated polyesters (UP) composites decreases the moisture pickup and increases the wet strength of reinforced plastic [48,49]. 

The mechanical properties of composites reinforced with wood fibers and PVC or PS as resin can be improved by an isocyanate treatment of those cellulose fibers [41,50] or the polymer matrix [50]. Polymethylene-polyphenyl-isocianate (PMPPIC) in pure state or solution in plasticizer can be used. PMPPIC is chemically linked to the cellulose matrix through strong covalent bonds (Fig. 8). 

Molten salts are characterized by the formation of discrete complex ions that are subjected to coordination phenomenon. Such complex ions have specific compositions that are related to the rearrangement of their electronic configuration and to the formation of partially covalent bonds. The life time of the coordinated ions is longer than the contact period of the individual ions [293]. 

In Section 18-6.3 the composition of proteins was given. They are large, amide-linked polymers of amino acids. However, the long chain formula (Figure 18-14, p. 348) does not represent all that is known about the structure of proteins. It shows the covalent structure properly but does not indicate the relative positions of the atoms in space. 

---