The flexible chain is a flexible molecular chain that can be freely crimped to form random coils in solution. The flexible chain is a flexible molecular chain that can be freely crimped to form random coils in solution. The characteristic that the polymer long chain can curl in different degrees is called flexibility, which is a unique property of the polymer, the root cause of the high elasticity of rubber, and the main factor determining the polymer shape.

Flexible chain principle: The root of polymer chain flexibility is based on its long chain structure and the free rotation of each chain on the chain, and the polymer main chain is composed of thousands of covalent bonds. The σ-electron cloud of a single bond is cylindrical, axially symmetrical and internally rotating. Because the rotation of the bond never stops, the conformation of the adjacent bonds of the polymer chain also keeps changing. Its shape is curved, like a messy wire group, called random wire group. Because the internal rotation frequency of the single bond is very high, the shape of the random coil is constantly changing. The flexibility of polymer chain mainly depends on the structure of polymer main chain and substituent, and is also affected by the intermolecular interaction.

Flexible chain characteristics: In carbon chain polymers, the polarity z is small hydrocarbons. The intramolecular interaction is not large, the internal rotation barrier is small, and the polymer chain has greater flexibility, such as polyethylene, polypropylene and so on. The main chain of diene polymers contains double bonds. Although the double bond itself cannot undergo rotation, it makes the internal rotation of Z-adjacent single bonds easier, such as 1, 4-polybutadiene. The barrier of internal rotation around C-O,C-N,Si-O and other single bonds in hetero-chain polymers is smaller than that of C-C single bonds. Therefore, the molecular chains of a series of polymers such as polyester, polyamide, polydimethylsiloxane, and polyurethane are flexible chains.