Degree of polymerization

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.

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

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

M n = X n M o

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

Correlation with physical properties

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.