Polymer-based reactants

Reactants, polymer-based s. Polymer-based reactants... 

FIGURE 6.25 In this preparation of rocket fuel for the space shutde, powdered reactants are mixed with a liquid polymer base and hardened inside the booster rocket shell. 

The suspension process is practiced by only a few companies because it offers a higher degree of production control and product engineering during polymerization step. This process suspends the water-based reactant in a hydrocarbon-based solvent. The net result is that the suspension polymerization creates the primary polymer particle in the reactor rather than mechanically in postreactions stages. Performance enhancements can also be during or just after the reaction stage. 

Ten years ago, good model systems were found for epoxy networks. These were polymers based on monomeric diglycidyl ethers of some bisphenols cured by simple aromatic amines (primarily w-phenylenediamine — wPhDA). Polymers based on these reactants satisfied the requirements for such a model system in several points ... 

Historically, only the used calculation for the concentration of a precursor was available but, in 1995, the incorporated calculation was added. Where the percent incorporated can be determined and supported by analytical results, this method of calculation can lead to a lower percentage of certain reactants for decision-making instead of using the calculation for the percent used. A new polymer may also be chemically identical to an existing polymer based on the degree of the precursor s incorporation. One may suppose that under the polymer exemption promulgated in 1995, the two-percent... 

Both polymer glycosides and polymer esters of the first sugar unit have been made. No problems due to incompatibility of polymer and reactants have been reported. Since highly protected sugars are employed in the synthesis, the normal hydrophilic nature of the sugars seems to be decreased, making them compatible with styrene-based polymers. This also seems to permit the use of weakly polar solvents such as benzene and methylene chloride in oligosaccharide synthesis. 

Polycondensation is carried out in a stainless-steel reactor. Heat is applied after mixing to promote the endothermic dehydration and formation of a polymer melt. The m.w. and the desired properties of the p. are controlled by the kind and ratio of the base reactants, the use of coreactants (monobasic acids, amines, different kind of difunctional monomers, etc.) and by the heating rate. The diamines are normally used in excess to avoid imdesired branching and are stripped off after the reaction. The product is cooled for finishing and transferred in the final form for delivery pellets, extruded ropes, crushed resins, viscous liquids or solutions. 

Amphiphilic block copolymers are a class of compounds for which synthesis is often a major problem. Such polymers contain one or more hydrophilic blocks with high water solubility and one or more hydrophobic blocks, which are usually not water soluble. The polymers are usually made by linking the blocks by a condensation or addition reaction, and the incompatibility of the reactants often results in very long reaction times or incomplete yields. [One exception is the well-known family of block copolymers made from alkylene oxides, i.e., various types of ABA polymers based on poly(ethylene oxide)-poly(propylene oxide) and poly(ethylene oxide)-poly(butylene oxide). The synthesis of these polymers from the monomeric alkylene oxides is straightforward.]... 

The various expressions we have developed in this section relating p to the size of the polymer are all based on h. Accordingly, we note that the average reactant molecule in this mixture has a molecular weight of 100 as calculated above. Therefore the desired polymer has a value of = 50 based on this concept. 

Acid Chloride Reaction. In situations where the reactants are sensitive to high temperature or the polymer degrades before the melt poiat is reached, the acid chloride route is often used to produce the polyamide (47). The basic reaction ia the presence of a base, B , is as follows ... 

Since corrosion involves a reaction of a metal with its environment, control may be effected through either or both of the two reactants. Thus control could be based entirely on the selection of a particular metal or alloy in preference to all others or the rejection of metals in favour of a non-metallic material, e.g. by a glass-reinforced polymer (g.r.p.). At the other extreme control may be effected by using a less corrosion-resistant material and... 

At the start of interfacial polymerization, bisphenol A is dissolved in methylene chloride, then introduced into a reactor. Phosgene is injected into the reactor as a liquefied gas together with an aqueous solution of sodium hydroxide. The methylene chloride and the aqueous solutions are immiscible polymerization occurs at the interface between them. The reactants are combined in a rapidly stirred reactor as shown in Fig. 20.7. The sodium hydroxide neutralizes the hydrochloric acid that is generated by polymerization, while the organic phase serves as a solvent for the polymer. The organic phase is separated and washed to remove traces of the base or salts after which the solvent is removed. 

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