Association in anionic polymerization. Its effect on the polymerization mechanism

A critical analysis is presented of the measurement and interpretation of association phenomena in anionic polymerization in non-polar solvents. In chain initiation, measured differences in reaction order arise because of differences in the way the process is defined. Some also may be caused by the extreme sensitivity of these systems to traces of polar impurities. In chain propagation, differences in measured association numbers of the active centers exist in diene polymerization. These can be caused by problems in the experimental technique. This is illustrated by data on concentrated solution viscosity measurements on linear and regular four-star polystyrenes and polyisoprenes as models for dimeric and tetrameric association.