Miniemulsion Polymerisation Via Reversible Addition Fragmentation Chain Transfer in Pseudo‐Bulk Regime

Abstract

A mathematical model of reversible addition fragmentation chain transfer (RAFT) living miniemulsion polymerisation based on pseudo‐bulk kinetics was developed and validated successfully with experimental data. In this work, in case of large particles synthesis by RAFT miniemulsion polymerisation greater than cross‐over size, the developed mathematical model in pseudo‐bulk regime reasonably matches with the experimental results and predicts the key polymer properties such as average molecular weight and MWD, average particle size and PSD. Consequently, optimal strategy of semi‐batch operation was developed using monomer and RAFT agent feed rate as process variables with specified initial conditions.

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

“…Nevertheless, a differentiation is made between the initial oligomeric RAFT agent and the polymeric dormant species in order to isolate the RAFT initiation stage from the overall kinetics. For simplicity, the average particle diameter d p and the average particle volume v p are considered constant throughout the entire polymerization process, in agreement with other modeling studies [ 105 , 107 , 120 ].…”

“…Despite that the investigation of RAFT in (mini)emulsion polymerization can be advantageous to investigate the plausibility of the chosen retardation model, a detailed kinetic study over a wide range of theoretically relevant RAFT addition, fragmentation, and cross-termination rate coefficients as a function of the average particle size is still lacking. Most kinetic modeling studies on RAFT (mini)emulsion polymerization are simplified [ 23 , 32 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 ] with the common assumption [ 23 , 103 , 104 , 110 , 112 ] of a zero-one system, hence, either droplets/particles contain one or no radical at all. For example, Altarawneh et al [ 103 , 104 ] used a zero-one model to describe the RAFT emulsion polymerization of styrene mediated by O -ethylxanthyl ethyl propionate.…”

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

“…To somewhat simplify the emulsion kinetics, focus has been on miniemulsion RAFT polymerization with an oil-soluble RAFT and/or oil-soluble radical initiator agent in which the polymer formation takes place in nanoscale monomer droplets so that the particle nucleation mechanism is less an issue (Figure ; blue box). ,,, RAFT miniemulsion polymerization can be achieved by applying high shear homogenization or ultrasonication to a mixture of monomer, water, initiator, RAFT agent, surfactant, and long-chain costabilizer which results in kinetically stable droplets with a diameter in the range 50–500 nm. ,,,− Consequently, before the onset of the polymerization, the (oil-soluble) RAFT agent is already evenly distributed over the droplets which obviates the necessity of aqueous phase transport of these hydrophobic molecules . Under well-defined conditions the droplets/particles are stabilized to such a degree that they do not coalesce or aggregate during polymerization, and hence, the final latex particle size distribution is very similar to the initial monomer droplet size distribution.…”

“…Several kinetic models have been also developed to better grasp RAFT miniemulsion polymerization. ,,,,− Focus has been on both stochastic and deterministic methods, typically neglecting diffusional limitations at the microscale, considering an average particle size, and simulating only the polymerization rate and thus the monomer conversion profile. By means of intrinsic kinetic Monte Carlo ( k MC) modeling, the influence of the RAFT agent during the early stages of the miniemulsion RAFT polymerization (<25% monomer conversion) on the monomer conversion and the relevance of exit/entry has been for instance investigated by Luo et al, with styrene and 1-phenylethyl phenyldithioacetate (PEPDA).…”

“…As macro-RAFT agents were considered exit and entry events were ignored, and with the intrinsic kinetic model the observed rate retardation was attributed to the establishment of a zero–one system in which intermediate radicals inside particles do not propagate. Also, pseudobulk minimemulsion kinetics have been modeled, for instance, with O -ethylxanthyl­ethyl propionate as RAFT agent and styrene as a monomer (semibatch operation mode) by a combination of population balances and approximate analytical equations . Focus was on high monomer conversions (e.g., 95%) while accounting for diffusional limitations on termination, although neglecting entry and exit phenomena originating from the initial RAFT agent.…”