There is significant demand for copolymeric materials with well-defined microstructures for use in highly specialized applications. In particular, work by Torkelson and coworkers has demonstrated that gradient copolymers, in which the composition smoothly changes from one monomer type to a second, provide a more stable interface to coarsening in order to compatibilize diferent homopolymers. A robust synthesis method commonly employed to create these materials is nitroxide mediated controlled radical polymerization (NM-CRP) in which a stable nitroxide radical is utilized to maintain control over a free radical polymerization. The addition of the nitroxide radical inhibits the effects of biradical termination reactions that account for the polydisperse nature of radical polymerization. NM-CRP has been successfully utilized in a number of systems to create structured copolymeric materials while maintaining a narrow polydispersity.
The Broadbelt group has focused on the development of the first stochastic kinetic models based on kinetic Monte Carlo (KMC) that are mechanistically based for the prediction of copolymer topologies. The group has used the KMC framework to describe the NM-CRP of copolymerization of various monomers with different reactivity ratios. KMC enables the explicit description of key characteristics of copolymerization systems including product evolution, molecular weight distribution, and chemical composition distribution. As shown in the figure below, the chemical composition distribution can be used as a “fingerprint” of the copolymer topology, and the modeling framework can be used to understand what reaction conditions and monomer pairs lead to successful creation of a copolymer with a desired backbone architecture.
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