Molecular Weight Control in Emulsion Polymerization by Catalytic Chain Transfer: A Reaction Engineering Approach

Abstract

Summary: For the application of catalytic chain transfer in (mini)emulsion polymerization, catalyst partitioning and deactivation are key parameters that govern the actual catalyst concentration at the locus of polymerization and consequently the final molecular weight distribution. A global model, based on the Mayo equation, catalyst partitioning and deactivation was developed. The influence of several reaction parameters on the instantaneous number average molecular weight was quantified.

The effect of Co(II)‐mediated catalytic chain transfer on the emulsion polymerization kinetics of methyl methacrylate

“…To summarize, the effect a catalytic chain transfer agent has on the course of the emulsion polymerization depends on the partitioning behavior. In the case of COBF in MMA emulsion polymerization the partitioning was determined at 0.72 dm dm,19 which is in good agreement with previously reported values for this system 11, 14. For the emulsion polymerization recipe used throughout this work ($\beta = {V_{\rm M}\over V_{\rm W}}$ = 0.185; solids content is 15 wt %; where V M and V W are the volume of the monomer and water phase, respectively) this results in a situation where 88% of the total absolute amount of COBF is present in the aqueous phase, independent of the amount of catalytic chain transfer agent added.…”

“…The discrepancy may be attributed to either COBF decomposition in the aqueous phase or the increasing viscosity inside the polymer particles. First, even under optimal conditions, some COBF decomposition can occur,19 shifting the instantaneous degrees of polymerization to the higher end of the molecular weight distribution. Secondly, toward higher conversions, the viscosity inside the polymer particles is increasing, which limits the mobility of COBF.…”

“…The objective of this investigation was to evaluate the effect of a commonly used and fairly water soluble ($m_{\rm Co} = {[{\rm Co}]_{\rm M}\over[{\rm Co}]_{\rm W}} = 0.72\ \rm{dm}^3_{\rm W}\, \rm{dm}^{-3}_{\rm M}$ )19 CCTA, bis[(difluoroboryl) dimethylglyoximato]cobalt(II) (COBF) on the ab initio emulsion polymerization of methyl methacrylate (MMA). This catalyst was selected to clearly and explicitly study both the aqueous phase and the polymer particle phase effects on the course of the emulsion polymerization.…”

The synthesis of translucent polymer nanolatexes via microemulsion polymerization

“…This marginal effect of the viscosity can be attributed to the relatively high ionic strength of the continuous phase. The cobalt(II) complexes used in dispersed phase CCTP are susceptible to deactivation in the aqueous phase at low pH [18,35]. As the V50 initiator is added as an HCl salt, typically a small amount of buffer (=NaH-CO 3 ) is added to minimize deactivation.…”

Methacrylic block copolymers by sulfur free RAFT (SF RAFT) free radical emulsion polymerisation

“…The activity of CoBF in emulsion CCTP also depends on the glass transition temperature (T g ) of latex particles. [40][41][42][43]45 In order to maintain an efficient chain transfer rate, the T g should be below the reaction temperature allowing for the catalyst to diffuse into the particles without hindrance. The reaction is controlled by a monomer feed that keeps the instantaneous conversion at approximately 50% resulting in the T g of the particle to be below the reaction temperature thus allowing for mobility between the phases.…”