Polymers whose macromolecules are composed of identical monomer units are called “homopolymers”, and if different monomer units form the macromolecules, such polymers are referred to as “copolymers”. By their origin all polymers are classified into natural (biopolymers) and synthetic. Biopolymers include proteins, nucleic acids, polysaccharides, cellulose, etc. Synthetic polymers are made from low molecular compounds (monomers) by means of polymerisation reactions, polycondensation or chemical modification of existing polymers.
For example, polystyrene is produced by the polymerisation of styrene, and polyvinyl alcohol by hydrolysis of polyvinyl acetate.
Macromolecules can have a linear structure, or can be branched or have a mesh-like three-dimensional structure (polymer networks). Examples of linear macromolecules include macromolecules of natural rubber, cellulose, some proteins, nucleic acids, regular polyethylene, polyamides and polyesters obtained by polycondensation of bifunctional monomers, etc. Examples of synthetic branched macromolecules include polyethylene produced under high pressure, graft copolymers, polymers, synthesised by polycondensation with tri-or tetrafunctional monomers; natural macromolecules are amylopectin, glycogen, etc. Spatial arrangement of a macromolecule is called “conformation”.
The simplest conformations include globular and unfolded (random coil) forms. The most important example of conformational transition is the denaturation of proteins by heating, where macromolecules pass from the folded globular conformation to the unfolded form. Other important characteristics of macromolecules include molecular weight, degree of polymerisation and polydispersity, as well as configuration of monomer units and of the chain.
- Khokhlov Alexey R.
- Govorun Elena N.