Chain configuration of macromolecules

Polymers are said to be linear if the repeating unit is joined together like a chain. The chain may be branched or joined together by cross-links of both. Thus more extensive cross-linking may lead to the formation of the three-dimensional crosses linked polymers.

Structural isomers of polymers

If we consider the polymerization of the monomer CH 2 = CHZ then there are three stereoisomers that are possible.

  1. Isotactic polymer: All the Z groups are on the same side of the chain.
  2. Syndiotactic polymer: Z groups lie alternatively on each side of the chain.
  3. Atactic polymer: Z groups are randomly situated along the two sides of the chain.

The polymers chain may have an enormous number of the configuration of identical energy. Thus the simple theory of the polymer configuration is very much similar to the theory of random flight of gas molecules. It gave the constant free path, which corresponds to the chemical bond distance in the polymer.

Characteristics of macromolecules

The physical characteristic of macromolecules primarily depends on shape and size. The shape of macromolecules also varies some of them are nearly spherical, some of them rod-like again many of them collided chains rapidly folded.

  • When there cross-linking between the repeat unit or chains the macromolecules become rigid insoluble amorphous solid such as bakelite, vulcanized rubber, etc.
  • When the polymers are dissolved in the good solvent in which the interaction between monomers units. Hence the solvent molecules are as strong as those between monomers units. These polymers molecules show an extended random coil structure configuration.
  • But when the polymer is dissolved in the poor solvent in which the interaction between monomer units and solvent molecules is weaker. Thus the polymer molecules show a compact configuration.

Common examples of polymers

For example, a random chain configuration is assumed by polypeptide ( protein) molecules in the solution. The hydrogen bond was not formed in this solution. The chains rotate around carbon atoms to which side groups are attached.

The reversible transition can occur between the alpha-helix structure and the random chain configuration of polypeptide depends on the pH scale of the solution.

  1. Isotactic polymer: All the Z groups are on the same side of the chain.
  2. Syndiotactic polymer: Z groups lie alternatively on each side of the chain.
  3. Atactic polymer: Z groups are randomly situated along the two sides of the chain.
  • When there cross-linking between the repeat unit or chains the macromolecules become rigid insoluble amorphous solid such as bakelite, vulcanized rubber, etc.
  • When the polymers are dissolved in the good solvent in which the interaction between monomers units. Hence the solvent molecules are as strong as those between monomers units. These polymers molecules show an extended random coil structure configuration.
  • But when the polymer is dissolved in the poor solvent in which the interaction between monomer units and solvent molecules is weaker. Thus the polymer molecules show a compact configuration.

Originally published at https://studychem.livejournal.com.

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