Molecular weight of polystyrene polymer obtained in the emulsion polymerization at low monomer concentration and the harkins–smith–ewart–gardon (HSEG) theory

The shape of the yield–time curves in the emulsion polymerization of styrene is a function of the recipe composition. Three types of yield–time curve were observed: (1) sigmoidal, (2) linear from the onset of polymerization, and (3) concave to the time axis; that is, the rate falls off continuously from the outset of polymerization. The viscosity‐average molecular weights ( M̄ v ) of the polymers in a given run are approximately parallel to the average rate of polymerization [i.e.,(yield of polymer at time t )/(time t )]. The Harkin–Smith–Ewart–Gardon (HSEG) theory provides a qualitative description of the emulsion polymerization of styrene at low monomer concentration if the yield–time curve is sigmoidal. From Gardon's equations it is found that the average number of radicals per particle ( Q ) varies from 0.5 to 2.0, depending on the composition of the recipe. The ( M̄ v ) expt /( M̄ v ) calc ratio lies between 1 and 2. The termination/propagation rate constant ( k t / k p ) ratio is a function of the composition of the recipe at a given temperature of polymerization and varies from 0.78 to 11.5 when it is estimated from the experimental data. The theoretical value, however, is 117.0. It has been shown that for a polydisperse system with particles of radius ( r ) between 10 and 1000 Å the maximum number of latex particles ( N 1 )/ml of the aqueous phase would be 10 19 –10 13 ; that is, if 10 ≤ r ≤ 1000 Å, then 5.97 × 10 19 ≥ N 1 ≥ 5.97 × 10 13 /ml.