Solution-melt polymerization techniqu

PA 66 prepolymer is prepared through a solution-melt polymerization technique, starting from the aqueous PA 66... 

This reaction occurs rapidly in the presence of an acid acceptor under mild conditions. The conventional melt polymerization techniques, as used for the preparation of nylons, cannot be applied to aromatic polyamides since the melting points of the polymers are too high. Polymerization is therefore conducted either in solution (e.g., in methylene chloride) or in suspension. In the latter case, the diamine is dissolved in water, together with an acid acceptor (e.g., sodium carbonate) and the diacid chloride is dissolved in a solvent which is immiscible with water (e.g., carbon tetrachloride or cyclohexanone). The two solutions are then subjected to intensive mixing. Rapid reaction occurs at the liquid interface or just inside the solvent boundary and this technique is therefore commonly termed interfacial polymerization. 

An overview of the synthesis and characterization of a unique class of polymers with a phosphorus-nitrogen backbone Is presented, with a focus on poly(dichloro-phosphazene) as a common Intermediate for a wide variety of poly(organophosphazenes). Melt and solution polymerization techniques are Illustrated, Including the role of catalysts. The elucidation of chain structure and molecular weight by various dilute solution techniques Is considered. Factors which determine the properties of polymers derived from poly(dichlorophos-phazene) are discussed, with an emphasis on the role that the organic substituent can play In determining the final properties. 

Polycondensation can be carried out by various polymerization techniques including melt polymerization, solution polymerization, interfacial polymerization, emulsion polymerization and solid-state polymerization. These polymerization processes will be summarized briefly in the following paragraphs. 

In 1975, Kellyprepared and characterized a number of polyesters based on 2,5-disubstituted furans in various states of reduction. In this study, 2,5-disubstituted-furan, -dihydrofuran, and -tetrahydrofuran monomers were polymerized using solution, melt-transesterification, ring-opening, and interfacial techniques. These monomers included diacids, diols, diacid chlorides, diesters, dicarboxylic acid anhydrides, as well as monomers based on 5-hydroxymethyl-2-furoic and tetrahydrofuroic acids and esters, and bycyclic lactones containing the tetrahydrofuran ring. A thorough review of previous work done in the area of poljnner synthesis, based on 2,5-disubstituted furan derivatives is reported. It is reported that when... 

As discussed earlier, the predominant polymerization technique for PA 6.6 formation is the solution-melt process. However, despite the commercial importance of the latter process, few efforts have been reported to expand it on nanocomposites formation by in-situ polymerizing the monomers in the presence of the nanofiller. Notably, although the in-situ intercalation process has been extensively, successfully, and commercially applied for the preparation of lactam/amino acid-based nanocomposites, for example, PA 6, a different picture is presented in diamine-and diacid-based nanocomposites, for example, PA 6.6, mainly characterized by the poor pertinent literature and lack of commercial application. 

Several techniques may be used to produce polymer-MMT nanocomposites, including in-situ polymerization, melt intercalation, and solution casting however, to date in-situ polymerization has produced the best dispersed systems for PS-MMT nanocomposites [8]. This technique offers the advantage of allowing the monomer to penetrate the intergallery spaces first, which aids the exfoliation process. If the polymerization reaction can occur between the clay layers, the delamination process is further enhanced as growing polymer chains can push the clay layers apart, which is the main reason for the superior dispersed systems observed [8]. There are several in-situ polymerization techniques which may be used to form... 

Essentially two strategies have been considered to prepare polymerlayered silicate nanocomposites. In the so-called intercalative polymerization, the layered silicate is swollen within the liquid monomer (or a monomer solution) so as the polymer formation can occur in between the intercalated sheets. Polymerization is usually promoted either by heat or an appropriate catalyst. In another technique, the layered silicate is mixed with the polymer matrix in the molten state. Under these conditions and if the layer surfaces are enough compatible with the chosen polymer, the polymer can crawl into the interlayer space and form either an intercalated or an exfoliated nanocomposite. In this melt intercalation technique, no solvent is required. 

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