Emulsion/miniemulsion polymerization of butyl acrylate with the cumene hydroperoxide/tetraethlenepentamine redox initiator

The macro- and miniemulsion polymerization of butyl acrylate (BA) with cume ne hydroperoxide/tetraethlenepentamine (CHP/-TEPA) as a redox initiator sys tem was investigated. It was found that the rate of polymerization was mono tonically decreasing rather than going through a maximum as is common in em ulsion polymerization. Furthermore, the polymerization rate at high monomer conversion of macroemulsion polymerization was unexpectedly decreased with an increase in initiator concentration. For miniemulsion polymerization, t he polymerization stopped at rather low conversion. It was also found that the average number of free radicals per particle dropped very quickly with polymerization time. With increased initiator concentration, the average nu mber of radicals per particle decreased in the macroemulsion polymerization . Molecular weight analysis indicated that aqueous phase polymerization, in terfacial polymerization and particle polymerization take place simultaneou sly. It is proposed that TEPA plays two roles in the polymerization; it is both a reducing agent in the redox initiator system, and a chain transfer a gent. All the unexpected results are well explained by postulating this mul tiple function of TEPA and taking the heterogeneous nature of emulsion poly merization into account.