Cross-linked polymer mixtures, synthetic

Synthetic Sequence Effects on Cross-Linked Polymer Mixtures... 

A polymer is a macromolecule that is constructed by chemically linking together a sequent of molecular fragments. In simple synthetic polymers such as polyethylene or polystyrer all of the molecular fragments comprise the same basic unit (or monomer). Other poly me contain mixtures of monomers. Proteins, for example, are polypeptide chains in which eac unit is one of the twenty amino acids. Cross-linking between different chains gives rise to j-further variations in the constitution and structure of a polymer. All of these features me affect the overall properties of the molecule, sometimes in a dramatic way. Moreover, or... 

In contrast to agarose, polyacrylamide is a synthetic polymer, and gel formation depends on chemical cross-linking. The bifunctional acrylamide derivative, N,N -methylene-6is-acrylamide is included in the polymerisation mixture to insert cross-links between chains of... 

A new synthetic strategy for incorporating a wide variety of NLO chromophores into PFCB polymers has been developed by Ma et al. [ 100]. The chromophore loading can be tuned by varying the ratio of chromophore-substituted di-TFVE monomer and the tri-TFVE inert monomer. The obtained mixture is then prepolymerized at 150°C, spin-coated to obtain high-quality films, and efficiently cross-linked at 180-250°C. All resulting NLO PFCB (Fig. 4.11) thermosets possess excellent solvent resistance,... 

Synthetic polymers can be classified as thermo-plasts, which soften under heat and can be reversibly melted, and thermosets, which by the action of heat or chemical substance undergo chemical reaction and form insoluble materials that cannot be melted. Mixtures of molecules of relatively low molar mass (hundreds to thousands) that are able to react mutually or with other compounds and form cross-linked materials are often called synthetic resins. That is, synthetic resins such as epoxy or polyester or phenol-formaldehyde resins are thermosets. The term oligomer refers to a polymer molecule with relatively low molar mass (roughly below 10 000 g mol whose properties vary significantly with the removal of one or a few of the units. 

Synthetic fibres with ion-exchange properties were obtained from tapes extruded from polystyrene or its mixtures with polyethylene or polypropylene, by chlorosulfonation by chlorosulfonic acid for cross-linking, followed by treatment with aniline. Ion-exchange composite spun fibres have also been synthesized from a thermoplastic polymer and an aromatic vinyl polymer by immersion of the drawn fibres in chlorosulfonic acid at 20 °C, followed by treatment with dichloromethane, methanol and 10% sodium hydroxide, and drying to yield fibres with an ion-exchange capacity of 2.1 mequiv.g" . ... 

Addition of butadiene to ethene polymerizations gives cross-linked material, but dienes are themselves important substrates for polymerization reactions. Natural rubber is an all-ds polymer of isoprene (Figure 21.10), which we encountered in Chapter 11, as an important precursor of the terpenes. Synthetic rubber made by radical polymerization is a mixture of cis- and trans-polyisoprene, (21.10). The material produced by metal-catalyzed polymerization is, however, all-ds and essentially identical to natural rubber. 

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