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Block copolymers are a unique class of polymeric materials that can be used, for example, as dispersants, compatibilizers, and viscosity modifiers. However, free radical synthesis of block copolymers has been difficult due to the propensity of the propagating chains to undergo premature irreversible termination. [1][2][3] In 1993, we reported the use of stable free radical nitroxides (e.g., TEMPO) to control free radical polymerization, thus enabling the synthesis of resins with controlled molecular weights and narrow polydispersities. 4

The recapping kinetics of a series of unimolecular initiators for free radical polymerization were investigated. The rate constants for the trapping of various carbon-centered radicals were analyzed as a function of structurally different nitroxides in order to determine suitable candidates for living free radical polymerization (LFRP). The technique of laser flash photolysis was used to determine the trapping rate constants for the radicals in the presence of various amounts of nitroxide and to also gain insight into the properties of the LFRP process.

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