MWD control in continuous free‐radical polymerizations through forced oscillations of the transfer agent feed

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Abstract
This paper studies the effect of forced‐feed oscillations of an intentionally added chain transfer agent on isothermal free‐radical polymerizations carried out in continuous stirred‐tank reactors (CSTRs). A solution polymerization is first considered. The influence on the molecular weight distribution (MWD) of rectangular waves and impulsive trains of the transfer agent feed is theoretically and experimentally investigated. The main result is that (within certain limits) the average polydispersity can be increased at will with respect to its corresponding steady‐state (SS) value, without affecting the average number average chain length or the instantaneous monomer and initiator conversions. This result is extended to an emulsion copolymerization under sinusoidal oscillations of the transfer agent feed, where the “decoupling” between the average molecular polydispersity and other parameters (conversions, number average molecular weight, average number of branches per molecule, and the particle‐size distribution) is also produced.