(559d) Mechanistic Modeling of Nitroxide-Mediated Controlled Radical Polymerization

Modern applications involving copolymeric materials require well-defined architectures commonly defined at the nano and microscale for highly specialized applications. A robust synthesis method capable of accomplishing controlled syntheses of polymeric materials is nitroxide-mediated controlled radical polymerization (NM-CRP). In this variant of free radical polymerization, a stable nitroxide radical is utilized to maintain control of the polymerization by inhibiting the effects of biradical termination reactions. By limiting the random nature of the termination mechanism, chains grow at a more uniform rate allowing for control over molecular weight and architecture while maintaining a narrow polydispersity.

Our research focuses on the use of experimental techniques and kinetic modeling tools to describe the homopolymerization and copolymerization of styrenic monomers (styrene and 4-acetoxystyrene) via NM-CRP. An alkoxyamine, α-methyl-styryl-di-tert-butyl nitroxide (A-T), was used as a unimolecular initiator to conduct polymerization at lower temperatures to reduce the effects of thermal initiation. Upon heating, the alkoxyamine will dissociate into a propagating alkyl radical and a nitroxide radical which reversibly recombines with propagating radical chains. NM-CRP using A-T has been successfully employed in the controlled homopolymerization and copolymerization of styrene and 4-acetoxystyrene.

This research focuses on the development of kinetic models describing the NM-CRP of 4-acetoxystyrene and its copolymerization with styrene. Previous modeling studies involved the use of continuum models based on the method of moments to successfully describe the kinetics of these systems. We now turn to the use of stochastic models based on kinetic Monte Carlo to describe these systems. The use of such models allows for a more explicit description of the key characteristics of copolymerization systems including species evolution, molecular weight distribution, and chain sequencing. The development of this framework as well as approaches used to handle the inherent stiffness of the system due to large differences in reaction timescales will be discussed, and results for styrene and 4-acetoxystrene homopolymerization and copolymerization will be presented.