Online Monitoring of Controlled Radical Polymerization:  Nitroxide-Mediated Gradient Copolymerization

A comprehensive characterization of the controlled radical copolymerization of styrene and n-butyl acrylate comonomers is obtained by using a recently introduced method termed automatic continuous online monitoring of polymerization reactions (ACOMP). By simultaneously monitoring and combining signals from a continuously diluted reactor stream, light scattering, viscosity, differential refractive index, and UV absorption were used, in a model-independent fashion, to follow the weight-average molecular weight M w, weight-average intrinsic viscosity [η]w, the concentrations of each comonomer, and hence also the evolution of the average instantaneous and cumulative compositions along the chains as comonomers were consumed. The “composition profile” along the chain will largely influence the copolymer properties, and it is suggested that gradient copolymers might also be termed “profiled copolymers”, which then includes di- and multiblock polymers. Invoking the Mayo−Lewis model allowed sequence length averages and reactivity ratios to be computed. It is believed that the use of ACOMP with gradient copolymerization will lead to a better understanding of underlying kinetics and mechanisms and eventually lead to the ability to control the composition profile formation during the polymerization reaction.