Degree of polymerization

As the number of polymerization of the monomer is referred to in a polymer molecule. It is identical to the ratio of the molecular weights of the polymer and its repeat unit. The exact number may, in addition to proteins, mostly just be an average over the sample under consideration. Only by strictly controlled stepwise synthesis (like proteins ) macromolecules can be obtained with completely uniform polydispersity.

The polydispersity of engineered polymers varies between 1.1 (anionic polymerization, controlled radical polymerization ), two ( ideal stepwise polyaddition) and up to 10 for processes with nonuniform kinetics and termination reactions (common in cationic, radical and coordinative polymerization).

The absolute value of the degree of polymerization is also strongly dependent on the process. When Anionik may, for example these can be set relatively accurate over a wide range ( the number of initiator molecules); other pathways it very much depends on the exact stoichiometry or about the discharge of the condensate.

The degree of polymerization of a sample is usually determined by their molecular weight. There are a number of methods, e.g. GPC, some method of determining the colligative properties (such as cryoscopy, vapor -pressure osmosis, ..), further viscometry, light scattering, etc. Still other methods are technically important, but that require an accurate calibration of the sampling system. Here we must mention the melt flow index method. Thus, for example, increased the viscosity of a plastic melt with increasing polymerization degree, the average value can be determined with the MFI method indirectly (ie relative to a chemically comparable standard ).

The degree of polymerization as well as the spatial distribution of the monomers in the molecule geometric ( that is, the stereochemical configuration of the molecule branches ) have great influence on the physical and especially the mechanical properties of a polymer.