2.2.2

The applet at left models chain growth systems using the Schulz distribution.  Recall from the previous section that the Schulz distribution is a two-parameter model (in contrast to the Flory distribution which is a one-parameter model, Section 2.1.3) where Xi and Wi are defined in terms of two parameters: a which is a measure of the coupling between polymer chains, and b which is related to a and the number average molecular weight, <Mn>. Since b can be specified in terms of a and <Mn>, then it is possible to specify only a and <Mn> to plot the Schulz distribution. This is a much more natural approach since <Mn> is a parameter that is commonly used to describe polymer systems.

The applet at left therefore requires the following quantities to be specified:

  • M0 -- molecular weight per repeat unit which in the case of chain growth systems is simply the molecular weight of the monomer
  • a -- positive value describing coupling that is typically between 0 and 1
  • <Mn> -- the number average molecular weight

Some things to investigate:

  • As a increases, what happens to the breadth of the distribution?
  • As a increases, what happens to the value of <Mw> / <Mn> (ie the polydispersity)?
  • As b increases, what happens to the breadth of the distribution?
  • How do the values of polydispersity compare with those for step growth polymerizations with the same value of <Mn>?