Final answer:
Polyamides formed from dicarboxylic acids and diamines, such as in the synthesis of nylon, tend to be more flexible due to the longer alkane chains acting as 'spacers' between amide linkages, compared to the shorter backbones of 2-amino acids in proteins.
Step-by-step explanation:
Polyamides are a type of polymer that can be synthesized through a condensation reaction between a dicarboxylic acid and a diamine. You are absolutely correct in observing that polyamides formed from dicarboxylic acids and diamines may be more flexible than those made from 2-amino acids. This flexibility can be attributed to the molecular structure of the polyamide. When a dicarboxylic acid, like adipic acid, reacts with a diamine such as hexanediamine, they form long chains with amide linkages -- typically illustrated in the synthesis of nylon polymers.
The reason for the enhanced flexibility lies in the longer alkane chains that separate the amide bonds as compared to 2-amino acids (also known as alpha-amino acids). These chains act as a 'spacer' between the rigid amide linkages, allowing for greater molecular motion and flexibility. One way to visualize this is thinking about a chain being easier to twist and bend when there are longer links between its rigid parts. In contrast, 2-amino acids, which are used to build proteins, have a shorter backbone between amide bonds, resulting in less flexibility.
Consequently, the polymer chains in polyamides made from dicarboxylic acids and diamines can slide past each other more easily, leading to materials that are more flexible. This flexibility makes these polyamides suitable for a variety of applications where such a property is desirable, ranging from textiles to engineering plastics.