SAN and ASA examples of properties

H2N-R-COOH leads to H2N-R-CO-(NH-R-CO-) -NH-R-COOH H2N-Ra-NH2 + HOOC-Rb-COOH lead to -(HN-Ra-NH-CO-Rb-CO) - 

The polyamides differ by the nature and lengths of the units between amide groups and by the arrangement of these amide groups. Certain properties are clearly affected by the length of the chains. 

The most commonly used polyamides are linear but special ones are semi-aromatic with an aromatic diacid and a linear diamine or a linear diacid and an aromatic diamine. 

All the PAs are engineering polymers with good mechanical performances, fair heat and fatigue resistances, interesting low-temperature behaviour, and resistance to oils, greases, hydrocarbons and numerous common solvents, but each subfamily has its features  

The amide groups of the backbone are hydrophilic and, consequently, polyamides are also hydrophilic, the more so the higher the amide ratio. The absorbed water plasticizes the polyamides leading to higher impact resistances and lower strengths and moduli. When comparing properties of various polyamides careful attention must be paid to the moisture content of the considered materials. Tests can be made on samples  

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