The hidden secrets of the average number of radicals per particle ([formula omitted]) and their implications in control of emulsion polymerization reactors

Abstract

Emulsion polymerization is the method of choice to produce waterborne polymers but is susceptible to run-to-run variations. This variability is hard to avoid because on-line measurement of many of the characteristics of interest, in particular the molar mass distribution (MMD) of non-linear polymers, is not possible. This work offers a way to solve this problem. First, it is shown that the average number of radicals per particle (n¯), a value that can easily be obtained from kinetic measurements, contains sufficient information to directly determine the distribution of particles with n radicals. It is then demonstrated that for a given measured MMD, knowledge of the distribution of radicals per particle allows solving the long standing problem of the accurate estimation of the effective termination rate coefficient in emulsion polymerization. Combining this knowledge, it is shown the value of n¯ alone (a value that can be obtained experimentally by calorimetric measurements) can be used to develop a soft sensor able to estimate on-line the molar mass distribution of highly non-linear polymers. This, for the first time, offers the possibility of on-line control of the MMD of non-linear emulsion polymers.