Characterization of polymers

Degree of polymerization

The number $\mathit{n}$ the basic building blocks united in a macromolecular chain is called the degree of polymerization $\mathrm{P.}$ designated.

${\mathrm{P.}}_{\text{n}}$ is defined as:

definition

${\mathrm{P.}}_{\text{n}}$ is the quotient of the number average of the molar mass of the high molecular weight substance and the molar mass of a basic building block. $\mathrm{P.}=\frac{{\mathrm{M.}}_{\text{polymer}}}{{\mathrm{M.}}_{\text{Basic building block}}}$

Most polymers consist of mixtures of polymers of different degrees of polymerization: they are polymolecular or molecularly non-uniform. The degree of polymerization of such polymers is therefore always an average value which still depends on the statistical weight used for the averaging. The numerical average value is particularly important

$${\overline{\mathrm{P.}}}_n=\frac{{\sum }_i{N}_i{\mathrm{P.}}_i}{{\sum }_i{N}_i}\begin{array}{l}{\overline{\mathit{P.}}}_{\text{n}}=\text{Number average degree of polymerization}\\ {\mathrm{P.}}_i=\text{Degree of polymerisation of the component}i\\ N_i=\text{Number of molecules}i\end{array}$$

and the mean of mass

$${\overline{\mathrm{P.}}}_w=\frac{{\sum }_i{m}_i{\mathrm{P.}}_i}{{\sum }_i{m}_i}\begin{array}{l}{\overline{\mathit{P.}}}_{\text{w}}=\text{Weight average degree of polymerization}\\ {\mathrm{P.}}_i=\text{Degree of polymerisation of the component}i\\ m_i=\text{Mass of the component}i=n_{\text{i}}{\mathrm{M.}}_{\text{i}}\end{array}$$

Video: 09-2 Polymers: Characterization Part 1 of 2 (May 2022).