Experimental Determination of Rp Dilatometry

26) shows, polymerization rates depend on the monomer and initiator concentrations. Since these concentrations are known most accurately at zero time, it is useful to work with initial rates of polymerization, as given by 

Unless otherwise specified all rates mentioned in the following sections will be initial rates and the superscript and subscript on Rp and (d[M]/(if), respectively, in Eq. (6.38) will be dropped. 

The dilatometer may be constructed in a variety of ways. The principle of operation of a dilatometer may be seen from the simple apparatus shown 

As soon as the solution has come to a thermal equilibrium, the volume of solution will decrease. The change in height of the liquid in the capillary is measured periodically with a cathetometer (a rigidly mounted, vertically sliding telescope) or from the scale on the dilatometer. The rate of poly- 

Problem 6.6 Show how the rate of a free-radical polymerization can be determined from the measured changes in the capillary liquid height (Ah) in a simple dilatometer (Fig. 6.1). 

---