Polyamides early investigations

Early investigations of the effect of water on the low-temperature relaxations of several aromatic polymers including polycarbonate, polyamides, and a polyurethane have shown several low-temperature anomalies (A .5). the case of a water-saturated... 

Clays have long been used as fillers in polymer systems because of low cost and the improved mechanical properties of the resulting polymer composites. If all other parameters are equal, the efficiency of a filler to improve the physical and mechanical properties of a polymer system is sensitive to its degree of dispersion in the polymer matrix (Krishnamoorti et ah, 1996). In the early 1990s, Toyota researchers (Okada et ah, 1990) discovered that treatment of montmorillonite (MMT) with amino acids allowed dispersion of the individual 1 nm thick silicate layers of the clay scale in polyamide on a molecular. Their hybrid material showed major improvements in physical and mechanical properties even at very low clay content (1.6 vol %). Since then, many researchers have performed investigations in the new field of polymer nano-composites. This has lead to further developments in the range of materials and synthesizing methods available. 

Polyamides and their analogue are also effective for the selective membranes and there have been developed many kinds of permselective membranes. In early 1960 s, du Pont started to investigate the membranes for demineralization of water by reverse osmosis. After screening polymers, aromatic polyamides and polyhydrazides were shown to have superior properties9-11. In the present review various polyamides and their analogue are in focus as barrier materials for membranes, and their permeative characteristics will be discussed from the view point of their chemical structures. 

Commercialization of polyamide/PP blends is still at an early stage. One of the commercial sources in the USA (D S International) offered two kinds of polyamide/PP blends, one rich in PP (DexPro ) and the other rich in polyamide (Dexlon ). The blend s improved dimensional stability over polyamide has led to some applications in automotive, lawn and power tool markets. The relative advantages of polyamide/PP blends vs. polyamide, PP and other blends have not been clearly identified and further market and application development is actively under investigation with several companies. 

J/n < 6,000). Often, no analytical data or structural characterization was provided. Room-temperature interfacial polycondensation methods were also investigated as a convenient alternative to classical polycondensations. Such methods were first reported for the preparation of polyamides and polyesters from the reaction of l,l -ferrocenyldi-carbonyl chloride with several diamines and diols. The synthesis of polyurethanes using this technique was also reported and involved the condensation of l,T-ferrocenedimethanol and l,T-bis(dihydroxyethyl)ferrocene with diisocyanates. Once again, however, these polymers possessed low molecular weights.The early research in these areas has been summarized and critically reviewed and will not be discussed further here. ... 

Thennal decomposition of aliphatic-aromatic polyamides was mainly investigated by Py-MS. It was found in an early study that the thermal degradation of copolyamides formed from aliphatic and aromatic amino acids occurred almost exclusively through the bond scission in the aliphatic moieties. It was shown by Py-EIMS that thermal degradation of copolyamides of p-aminobenzoic acid and some aliphatic amino acids yielded poly-p-aminobenzoic acid via the elimination of lactams ... 

Single crystals of organic polymers were observed as early as 1927 by Staudinger. It became the subject of intensive investigations after an observation that linear polyethylene can crystallize into single crystals. The observations made on polyethylene were followed by observations that it is possible to grow single crystals of other polymers. Some of them are polyoxymethylene, polyamides, polypropylene, polyoxyethylene, cellulose, and others. 

In isothermal determinations the shapes of CL intensity on time are individualize for different oxidation mechanisms involving specific free radicals. If polyolefins generate sigmoid form of CL curves [04G1], for polyamides [03C1] or polyurethanes [07J1] an early peak is recorded in CL intensity measurements followed by parabolic decrease. In any case, the CL intensity values on the first five minutes of measurements define the initial state of oxidation rather than the instant decomposition process. Either isothermal CL measurements or nonisothermal CL investigations are reliable and accurate tools for... 

During the course of these studies, W.H. Carothers and G.J. Berchet in 1930, extending the early work of von Braun, investigated the self-condensation of e-aminocaproic acid [ ]. They obtained a low-molecular polyamide. From cryoscopic measurements in phenol they inferred a degree of polymerization of at least 10. In the same paper they stated that caprolactam "does not polymerize under the conditions of formation of the polyamide either in the presence or absence of catalysts". As practically no experimental details were given, one can only speculate about the reason of this failure. Perhaps they were influenced by the fact that the corresponding 5- and 6-membered lactams did not polymerize either - an explanation offered later by P. Schlack [s]. 

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