By combining experimental and modeling tools, a detailed characterization study of MADIX properties becomes possible.

The polymerization rate and average polymer characteristics of degenerative reversible addition–fragmentation chain transfer (RAFT) miniemulsion polymerization of methyl methacrylate with cyanoprop-2-yl dithiobenzoate as initial RAFT agent (R0X) and potassium persulfate as initiator are studied at 333 K up to monomer conversions of 95%, considering a two-dimensional Smith–Ewart model. This model accounts for the number of macroradicals and R0 radicals per nanoparticle, an average particle size between 50 and 500 nm, targeted chain lengths (TCLs) between 50 and 600, exit/entry of R0 radicals, and the possible influence of diffusional limitations on termination and RAFT transfer at the microscale. The accuracy of the microscale model parameters is highlighted by a successful description of bulk literature data, and the interphase mesoscale parameters are determined based on literature miniemulsion data at various average particle sizes. It is demonstrated that at high monomer conversions it is not afforded to assume zero–one kinetics due to diffusional limitations on termination. With larger average chain lengths this deviation is more pronounced and further accelerated by diffusional limitation on RAFT transfer. Even though the miniemulsion kinetics are faster than the bulk counterpart, retardation due to consecutive entry/exit events of R0 radicals can be observed as long as R0X is present.

A 5-dimensional Smith-Ewart based model is developed to understand differences for reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization with theoretical agents mimicking cases of slow fragmentation, cross-termination, and ideal exchange while accounting for chain length and monomer conversion dependencies due to diffusional limitations. The focus is on styrene as a monomer, a water soluble initiator, and a macro-RAFT agent to avoid exit/entry of the RAFT leaving group radical. It is shown that with a too low RAFT fragmentation rate coefficient it is generally not afforded to consider zero-one kinetics (for the related intermediate radical type) and that with significant RAFT cross-termination the dead polymer product is dominantly originating from the RAFT intermediate radical. To allow the identification of the nature of the RAFT retardation it is recommended to experimentally investigate in the future the impact of the average particle size (dp) on both the monomer conversion profile and the average polymer properties for a sufficiently broad dp range, ideally including the bulk limit. With decreasing particle size both a slow RAFT fragmentation and a fast RAFT cross-termination result in a stronger segregation and thus rate acceleration. The particle size dependency is different, allowing further differentiation based on the variation of the dispersity and end-group functionality. Significant RAFT cross-termination is specifically associated with a strong dispersity increase at higher average particle sizes. Only with an ideal exchange it is afforded in the modeling to avoid the explicit calculation of the RAFT intermediate concentration evolution.

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