Chain extension three-dimensional cross-linking

The dimension of cross-linking (e.g., 1-, 2-, or 3-dimensional), the extension (as applies to, e.g., the inosilicates), and the number of cross-linked elements (e.g., 2 for double layers or double chains) are identified by the anion complex notation as proposed by Liebau [16]. The symbol 2/< of the anion complex of the metal silicate hydrates describes the two-dimensional cross-linking of the silicon oxygen tetrahedra to tetrahedral sheets. Following an older model, one, two, three, and five tetrahedral sheets are connected to form the bulk layer of kanemite or makatite, ilerite, magadiite, and kenyaite. 

These polymers are liquids which may usefully be cast or used for impregnation and caulking compounds. In addition they may be vulcanised by a variety of agents, ostensibly by a chain lengthening process. It should, however, be noted that these polymers normally contain small quantities of tri-chloropropane in the original monomer mix so that the three-dimensional chain extension will lead to cross-linking. 

Chcmically, Bakelite is a phenolic resin, produced by reaction of phenol and formaldehyde. On heating, water is eliminated, many cross-links form, and the polymer sets into a rocklike mass. The cross-linking in Bakelite and other thermosetting resins is three-dimensional and is so extensive that we can t really speak of polymer "chains." A piece of Bakelite is essentially one large molecule. 

A critical requirement for obtaining engineering properties from a rubbery material is its existence in a network structure. Charles Goodyear s discovery of vulcanization changed natural rubber from a material that became sticky when hot and brittle when cold into a material that could be used over a wide range of conditions. Basically, he had found a way to chemically connect the individual polymer chains into a three-dimensional network. Chains that previously could flow past one another under stress now had only limited extensibility, which allowed for the support of considerable stress and retraction upon release of the stress. The terms vulcanization, rubber cure, and cross-linking all refer to the same general phenomenon. 

The mechanical strength of polymers is achieved through extensive cross-linking whereby a three-dimensional network of hydrocarbon chains is formed. Depending... 

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