Other Aliphatic Polyamides

They have found use as hardeners-eum-flexibilisers for epoxide resins (see Chapter 26) and are of interest in the production of thixotropic paints and adhesives. Related higher molecular weight materials are tough and flexible and find use as hot melt adhesives (Versalons). 

As has been mentioned earlier, a number of copolymers such as nylon 66/610/6 are available. Sueh a copolymer has an irregular structure and thus interchain bonding and crystallisation are limited. As a consequence the copolymer is soluble in alcohols and many other common polar solvents. 

Where R H the amino acids may incorporated in either a D- or L-configuration and so it is possible for configurational polymers to be produced. There do not, however, show the same mechanical properties as the configurational homopolymers, which are more regular in structure. 

These polymers, typical of polyamides with fewer than four main chain carbon atoms in the repeating unit, decompose before melting and have to be processed from solution. Several of the polymers may, however, be spun into fibres. Over thirty years ago Courtaulds produced silk-like fibres on an experimental commercial scale from poly-(L-alanine) and from poly-(a-methyl-L-glutamate). The latter material is also said to be in use as a synthetic leather in Japan. The 

A typical example of this class of polymer may be obtained by reacting etfaylenediamine and dimer fatty acid , a material of inexact structure obtained by fractionating heat-polymerised unsaturated fatty oils and esters. An idealised structure for this acid is shown inFigirrc 7S.27. These materials are dark coloured, ranging from viscous liquids to brittle resins and with varying solubility. 

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It requires finishing temperatures of up to 300°C to complete the polymerization. Yields are almost quantitative so the finished polymer may be used directly. Nylon 12, too, has a relatively low-melting point and lower tensile strength in fiber or engineering applications than nylon 6,6 or nylon 6, like the other aliphatic polyamides described in this section (Table 21.4). It is interesting to note that nylon 6,6, the first of the aliphatic polyamides to be commercialized, also has the best properties for many purposes. 

Polyadipamides are less thermally stable than other aliphatic polyamides because they are subject to a chain-cleavage reaction that occurs at temperatures below 300 °C. This reaction involves adipamide cyclization (Reaction 43). 

Nylon-6,6 and nylon-6 are also used for plastics applications. Besides these two polyamides, very many other aliphatic polyamides, have been prepared in the laboratory, and a few of them (nylon-11, nylon-12, and nylon-6,10 in particular) have attracted specialized interest as plastics materials. However, only about 10% of the nylons produced are used for plastics production. Virtually all of the rest goes for the production of fibers where the market is shared, roughly equally, between nylon-6 and nylon-6,6. 

Other Aliphatic Polyamides. They are mainly polyamides having longer polymethylene sequences. Their marketing was dictated by the need of technical polymers whose mechanical characteristics are less sensitive to the hygrome-try of the ambient conditions than those of PA-6 and PA-6,6. It concerns PA-6,10, which is obtained by the polycondensation between hexamethylenediamine and sebacic acid [HOOC-(CH2)8-COOH], PA-11 and PA-12. 

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