Degree of polymerization

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The degree of polymerization, or DP, is the number of repeat units in an average polymer chain at time t in a polymerization reaction [1]. The length is in monomer units. The degree of polymerization is a measure of molecular weight. For most industrial purposes, lengths in the thousands or tens of thousands are desired.

For a homopolymer, the degree of polymerization may be calculated as shown below

DP = Total MW of the polymer/MW of the repeating unit

<math>M_n=X_nM_o</math>

In polycondensation, in order to achieve a high degree of polymerization (and hence molecular weight), Xn, a high fractional monomer conversion, p, is required, as per Carothers' equation: Xn = 1/(1−p). A monomer conversion of p = 99% would be required to achieve Xn = 100.

Correlation with physical properties

File:Degree of polymerization.PNG
Relationship between degree of polymerization and melting temperature for polyethylene. Data from Flory (1963).

Polymers with identical composition but different total molecular weights may exhibit different physical properties. In general, increasing degree of polymerization correlates with higher melting temperature [2] and higher mechanical strength.


See also

References

  1. Gold Book definition Link
  2. Flory, P.J. and Vrij, A. J. Am. Chem. Soc.; 1963; 85(22) pp3548-3553

ar:درجة بلمرة de:Polymerisationsgrad it:Grado di polimerizzazione