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Ab-initio-calculated rate coefficients for addition and fragmentation in reversible-addition fragmentation chain transfer (RAFT) polymerization of styrene with 2-cyano-2-propyl dodecyl trithiocarbonate initiated by azobisisobutyroni-trile allow the reliable simulation of the experimentally observed conversion, number average chain length, and dispersity. The rate coefficient for addition of a macroradical Ri to the macroRAFT agent RiX at 333 K (6.8 104 L mol-1 s-1) is significantly lower than to the initial RAFT agent R0X (3.2 106 L mol-1 s-1), mainly due to a difference in activation energy (15.4 vs 3.0 kJ mol-1), which causes the dispersity to spike in the beginning of the polymerization. [ABSTRACT FROM AUTHOR]

The importance of the development of kinetic modeling tools to mechanistically understand and design bulk and solution reversible addition fragmentation chain transfer (RAFT) polymerization is highlighted. Both deterministic and stochastic kinetic modeling methods are covered, considering a detailed reaction scheme and accounting for the impact of diffusional limitations on the reaction rates. A novel strategy is introduced to fundamentally calculate the diffusional contributions for the apparent RAFT addition and fragmentation rate coefficients. Next to literature examples, case studies are included to demonstrate that detailed theoretical studies are indispensable to completely map the effect of the polymerization conditions and RAFT agent reactivity on the control over microstructural properties and the overall polymerization time. Guidelines for future kinetic modeling activities are formulated to enhance joined theoretical and experimental research. [ABSTRACT FROM AUTHOR]

Under the validity of the degenerative transfer mechanism, the activation/deactivation process in reversible addition-fragmentation chain transfer (RAFT) polymerization can be formally quantified by transfer coefficients, depending on the chemical structure of the participating radicals and dormant species. In the present work, the different literature methods to experimentally determine these RAFT transfer coefficients are reviewed and theoretically re-evaluated. The accuracy of each method is mapped for a broad range of reaction conditions and RAFT transfer reactivities. General guidelines on when which method should be applied are formulated. [ABSTRACT FROM AUTHOR]

The superior capabilities of structured microreactors over batch reactors are demonstrated for reversible addition--fragmentation chain transfer (RAFT) solution polymerization of n -butyl acrylate with the aid of simulations, explicitly accounting for the chain length distribution of all macrospecies types. Since perfect isothermicity can be established in a microreactor, less side products due to backbiting and β-scission are formed compared to the batch operation in which ineffective heat removal leads to an undesirable temperature spike. For a given RAFT chain transfer agent (CTA), additional microstructural control results under microflow conditions by optimizing the reaction temperature, lowering the dilution degree, or decreasing the initial molar ratio of monomer to RAFT CTA. [ABSTRACT FROM AUTHOR]

Precisionfunctionality is the key feature of next-generation radical polymerizationenabling the implementation of applications such as controlled drugdelivery, self-healing material design, and optoelectronic materials.The incorporation of functionality is however diametrically opposedto diffusion-controlled growth-inhibiting termination reactions. Thefundamental bottleneck remains the identification of a generic andflexible protocol to accurately map the short–longtermination reactivity. Herein, we introduce a unique frameworkbased on the reversible addition–fragmentation chain transfer–chainlength dependent–termination (RAFT-CLD-T) method that encompassesan extension of state-of-the-art fundamental theories and a correctionfor possible polymer matrix effects. Applied to methyl methacrylate(MMA) polymerization, the short–longterminationreactivity is accurately quantified for the first time. Data analysisreveals the deficiency of currently used simplified models to describethe true short–longtermination reactivityand the dominance of short-chain diffusivity. The proposed frameworkand insights are a turnkey prerequisite for the fundamental understandingof radical polymerization processes and to complete current macromoleculardiffusion theories. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A pseudo-steady state based (PSSA) deterministic solution strategy is presented to calculate the concentrations of single and multi-arm macrospecies types in reversible addition fragmentation chain transfer (RAFT) polymerization, accounting for chain length dependent apparent rate coefficients to fully reflect the impact of diffusional limitations. The simulation time is of minute scale and diffusional limitation on termination are accounted for with the RAFT-chain length dependent-termination technique. Based on an extensive set of experimental data (18 conditions), addition and fragmentation kinetic parameters are determined for RAFT polymerization of styrene initiated by 2,2′-azobis(2-methylpropionitrile) and 2-cyano-2-propyl dodecyl trithiocarbonate. Due to higher chain length dependent apparent termination rates, a rate retardation with respect to the free radical polymerization (FRP) results despite that a simplified degenerative mechanism can be considered. This rate retardation is enhanced for polymerizations exhibiting a stronger gel-effect ( e.g. methyl methacrylate). Then even the average RAFT polymerization characteristics cannot be reliably calculated by approximating the macroradical chain length distribution (CLD) through a Poisson or Schulz-Flory distribution. The calculation of the macroradical CLD always requires a full kinetic model taking into account the chain length dependencies for all individual chain lengths. [ABSTRACT FROM AUTHOR]

We pioneer the synthesis of well-defined high molar mass segmented copolymers, employing a unique combination of step-growth and reversible addition-fragmentation chain transfer (RAFT) polymerization. The step-growth precursor polymer is obtained via the ambient temperature UV-light-induced Diels-Alder reaction of 6'-(propane-1,3-diylbis(oxy))bis(2-methylbenzaldehyde) (AA monomer) and di(isopropionic ethyl ester fumarate) trithiocarbonate (BB monomer). Unconventional off-stoichiometric conditions (r = [AA]0:[BB]0 = 1.5-1.75) are employed to ensure a sufficiently high incorporation of BB in the step-growth product (1200 ≤ Mn/g mol-1 ≤ 3950). The optimum r value is based on a detailed product distribution analysis, comparing experimental and bivariate kinetic Monte Carlo generated data, using a scheme of over 200 reactions. The analysis highlights the unexpected occurrence of AA homopolymerization and the ligation of the resulting AA segments at higher reaction times. The precursor step-growth polymer is successfully transformed into a segmented copolymer via insertion of styrene by RAFT polymerization at 60 °C (11 200 ≤ Mn/g mol-1 ≤ 53 400), as confirmed both experimentally and through simulations. [ABSTRACT FROM AUTHOR]