Deterministic Modeling of Degenerative RAFT Miniemulsion Polymerization Rate and Average Polymer Characteristics: Invalidity of Zero–One Nature at Higher Monomer Conversions

Abstract

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.

Modeling of Miniemulsion Polymerization of Styrene with Macro-RAFT Agents to Theoretically Compare Slow Fragmentation, Ideal Exchange and Cross-Termination Cases

“…The corresponding transfer “rate coefficients” ( k tr, 0 , k -tr, 0 and k tr ), as defined based on the (conventional) radical and dormant species concentrations, are a function of the elementary RAFT addition and fragmentation parameters: ktr,0=kadd,0,akfrag,0,bkfrag,0,a+kfrag,0,b k−tr,0=kadd,0,bkfrag,0,akfrag,0,a+kfrag,0,b ktr=kadd2 with in the last equation, for simplicity, chain length dependencies neglected, although the relevance of this assumption needs still further investigation and is probably RAFT specific [46,47]. Intrinsically this assumption can be realistic [47] but at higher monomer conversion the RAFT exchanges can be influenced by diffusional limitations [19,48,49,50,51,52,…”

Coupled stochastic simulation of the chain length and particle size distribution in miniemulsion radical copolymerization of styrene and N-vinylcaprolactam

“…[20][21][22][23][24][25][26][27] Ideally, micro-and meso-scale model parameters are respectively determined by careful parameter estimation to bulk and dispersed phase polymerization data. [28][29][30] Recent work of Marien et al 31 on radical miniemulsion homopolymerization has indicated that advanced kinetic Monte Carlo (kMC) modeling is very promising to handle the interactive evolution of the chain length distribution (CLD) and PSD in dispersed phase polymerization. Only by particle-by-particle tracking of the reaction and mass transfer events, as illustrated in Figure 1, it becomes possible to capture the correlation between chain and particle growth.…”

A simple model for the semicontinuous heterophase polymerization: Ethyl methacrylate as a case example

“…Regarding the models in the literature, almost all assume a 0‐1 system and very few present the molar mass evolution; therefore, the 0‐1 assumption cannot be corroborated unless a population balance of radicals is performed . Here, in spite of detecting a low value of ñ (less than 0.5), a model that is not 0‐1 is capable of an accurate description of conversion, particle density and degree of polymerization, better than in previous works.…”

“…In a RAFT miniemulsion polymerization of MMA with a two‐dimensional Smith−Ewart model, Devlaminck et al , accounted for the number of macroradicals and the R 0 radicals per nanoparticle, for average particle sizes between 50 and 500 nm, and targeted chain lengths between 50 and 600. They also considered entry and exit of R 0 radicals and the possible diffusional limitations on termination.…”