Chapter XV: Influence of the End Groups on the Properties of Polymers

The problem of influence of the molecular mass of the polymer and the problem of the end groups role and their influence on the properties associated with it has been discussed many times in the literature. For example, there are data on the dependence of glass transition temperature T _g and melting point T _m on the molecular mass in the shape of curves with a plateau, as well as information on other properties dependent on the molecular mass.

As an example, Figure 21 displays the dependence of T _g on the mean molecular mass of polystyrene. There is a series of correlations describing these dependences, for example [144],

where T _g(?) is the glass transition temperature of the polymer at the molecular mass M ? ?; k is the polymer constant.

Dependences of this kind do not describe T _g( M) curves along their length. More complicated dependence T _g( M) is of the form [145]:

where K* and M* are fitted parameters. Obviously, not only glass transition temperature T _g, but also all other properties depend on the molecular mass. Searching for these dependences is of special interest.

This problem is of prime importance for analysis of the molecular mass influence on the properties of propagating chains at a very low number of units n. The circumstance that the chemical structure of end groups may significantly (and even principally sometimes) differ from the structure...