Kinetics and Mechanism of Controlled Free-Radical Polymerization of Styrene and n-Butyl Acrylate in the Presence of an Acyclic β-Phosphonylated Nitroxide

Abstract

This study investigates the kinetics of free radical polymerization of styrene and n -butyl acrylate carried out in the presence of N - tert -butyl- N -[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide (DEPN). With this stable radical as chain growth moderator, it is demonstrated that the polymerization of these two monomers exhibits a controlled character. The mechanism of polymerization is essentially the same as that described for other “living”/controlled radical polymerizations: the chains form a large pool of dormant species that can be reversibly activated, and only a minute fraction of them propagate at a given time. Using dilatometry and electron spin resonance (ESR), the evolution of the concentration of polymeric radicals and that of DEPN could be measured as a function of time. It appears that these DEPN-mediated polymerizations are driven toward a pseudo-stationary state that is reached after an initial period of a few minutes. During this pseudo-stationary phase, the concentration of polymeric radicals and that of DEPN remained essentially constant, which allowed us to determine the ( K ) equilibrium constant between dormant and active species and also the rate constants of reversible activation ( k d ) and deactivation ( k rec ) for each monomer. For purposes of comparison, a series of polymerizations were simulated using the PREDICI package: both experimental and simulated data were found to fall in rather good agreement.