Chain transfer constants of mercaptans in the emulsion polymerization of styrene

The chain transfer reaction and overall consumption of three mercaptans ( n ‐decyl mercaptan. n ‐dodecyl mercaptan, and tert ‐dodecyl mercaptan) were studied in batch and semibatch seeded emulsion polymerizations of styrene. Seventy to ninety‐five percent of the mercaptans reacted by chain transfer. The apparent chain transfer constants of mercaptans in the batch process decreased with increasing carbon chain length of the mercaptans. This tendency is connected with the analogous difference of the distribution coefficients of these mercaptans between the water phase and monomer droplets. The values of the chain transfer constant are independent of the amount of mercaptans used and reaction temperatures from 60°C to 90°C. The chain transfer constant of tert ‐dodecyl mercaptan had the same value in both the batch and semibatch processes. This indicates that varying the concentrations of initiator and monomer had negligible effects on the chain transfer reaction.