Three-dimensional network of polymer

We noted above that the presence of monomer with a functionality greater than 2 results in branched polymer chains. This in turn produces a three-dimensional network of polymer under certain circumstances. The solubility and mechanical behavior of such materials depend critically on whether the extent of polymerization is above or below the threshold for the formation of this network. The threshold is described as the gel point, since the reaction mixture sets up or gels at this point. We have previously introduced the term thermosetting to describe these cross-linked polymeric materials. Because their mechanical properties are largely unaffected by temperature variations-in contrast to thermoplastic materials which become more fluid on heating-step-growth polymers that exceed the gel point are widely used as engineering materials. 

Traditionally, we create thermoset polymers during step growth polymerization by adding sufficient levels of a polyfunctional monomer to the reaction mixture so that an interconnected network can form. An example of a network formed from trifimctional monomers is shown in Fig. 2.12b). Each of the functional groups can react with compatible functional groups on monomers, dimers, trimers, oligomers, and polymers to create a three-dimensional network of polymer chains. 

Colloids have been described as classic polymer gels, and their dynamics in seawater may be understood in terms of polymer gel theory (Chin et al., 1998). Polymer gels are stable, three-dimensional networks of polymers and seawater (Figure 11). Gels assemble spontaneously from... 

Polymerisation is a process of reacting the same monomer together chemically to form a three-dimensional network of polymer chains. There are many forms of polymerisation... 

In step 1, functional monomer and template are connected by a covalent linkage (in covalent imprinting ) or they are placed nearby through non-covalent interactions (in non-covalent imprinting ). In step 2, the structures of these conjugates (or adducts) are frozen in a three-dimensional network of polymers. The functional residues (derived from the functional monomers) are topographically complementary to the template. In step 3, the template molecules are removed from the polymer. Here, the space in the polymer originally occupied by... 

ELASTICITY OF A THREE-DIMENSIONAL NETWORK OF POLYMER MOLECULES... 

III. Elasticity of a Three-Dimensional Network of Polymer Molecules... 

The chemical shift (8) for methyl protons of toluene [PhCHs] is 2.3 ppm and for methylene protons of bibenzyl (Ph—CH2CH2—Ph) is 2.9 ppm. In poly(phenylcarbyne), the terminal protons (>C(Ph)—CH(Ph)—C(Ph)<) are further deshielded since they bear more benzyl groups in the three-dimensional network of polymer. The chemical shift for these protons should be downfield to 3.5 ppm. 

Coverage The rate at which the paint spreads. The rate of spreading is expressed in square meters per liter. Cross-linking Establishment of chemical links between the molecular chains to form a three-dimensional network of polymers. Cross-Unking toughens the coating. DHuent A liquid which is used in conjunction with a solvent to improve the film properties. 

A linear polymer may also become cross-linked, which is the binding together of polymer chains at various places by means of strong covalent bonds, usually through the presence of foreign atoms. The result is a three-dimensional network of polymer chains in which the movement of the individual molecules is quite restricted. Network and cross-lined polymers are rarely crystalline, even to a limited extent, and may be treated as amorphous. 

The mechanisms of PVC fusion have been studied in detail by several researchers and a number of articles have been written (5,6). However, Rabinovitch and Summers were the first to describe in detail how the morphology of PVC changes during hot processing and provided clear mechanisms of PVC fusion (5,6). As described in their work PVC fusion is considered as the thermal reduction of particle boundary surface. In other terms, the process of PVC fusion is essentially a destruction of the original coarse powder structure (100-200 pm in diameter) to submicroparticles (approximately 10-30 nm in diameter) so that ey can be compacted. During further interdiffusion of fhe PVC, the boundaries between the submicroparticles disappear and a three dimensional network of polymer chain is formed. 

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