Nitroxide-Mediated Styrene Miniemulsion Polymerization

Abstract

Living radical polymerization of styrene was conducted in a miniemulsion using TEMPO and the water-soluble initiator potassium persulfate (KPS). The effects of initiator concentration and the TEMPO:KPS ratio on conversion, molecular weight distribution, and particle size were studied. The miniemulsion polymerizations exhibit similar characteristics to bulk living radical systems but with unique features attributable to the heterogeneous nature of the system. There is a strong interaction between the KPS concentration and the TEMPO:KPS ratio, and therefore the effects of changing either variable depend strongly on the value of the other variable. Initiator efficiencies are considerably higher than in conventional KPS-initiated styrene emulsion or miniemulsion polymerizations, while the average number of active radicals per particle (∼10-2) is much lower. Aqueous-phase kinetics and nitroxide partitioning determine the number of chains initiated and therefore also affect the polymerization rate and molecular weight.

Nitroxide‐Mediated Controlled/Living Free Radical Copolymerization of Styrene and Divinylbenzene in Aqueous Miniemulsion

“…The value of 0.009 is similar to values previously reported for the TEMPO-mediated miniemulsion polymerization of S in the absence of DVB. [23,27] Compartmentalization effects on bimolecular termination are therefore only expected to be significant in the miniemulsion with the smaller particles (as also suggested in a modeling study by Charleux [21] ), indicating that it is not the only factor causing different R p s in the three systems.…”

Particle Size Effects in TEMPO‐Mediated Radical Polymerization of Styrene in Aqueous Miniemulsion

“…[19,20] As far as we are aware, there are to date no systematic studies on particle size effects in NMP in miniemulsion, although scattered information exists with regards to differences between miniemulsion and bulk for TEMPO-mediated radical polymerization of S in miniemulsion. In most cases, S/TEMPO miniemulsion polymerizations using macroinitiator (polystyrene (PS)-TEMPO), [21,22] benzoyl peroxide/ TEMPO [23,24] or potassium persulfate/TEMPO [24][25][26][27] give R p values very similar to those in bulk. [28] Cunningham and coworkers [29,30] reported a strong dependence of R p in S/PS-TEMPO miniemulsion on the amount of the surfactant sodium dodecylbenzenesulfonate (SDBS) (the particle size distributions were ''nearly identical'' with a ''mean diameter'' of 150 nm), and speculated that SDBS or SDBS impurities consume nitroxide, thus resulting in an increase in R p .…”

Controlled/Living Radical Polymerization in Aqueous Miniemulsion

“…This result was explained by partition of the TEMPO between the organic and the aqueous phase, which would lead to a significant decrease of the nitroxide concentration in the polymerization locus. While TEMPO-or TEMPO-OH-terminated polystyrene were used as macroinitiators for the miniemulsion polymerization of n-butyl acrylate (nBA) to prepare the corresponding block copolymers by simple chain extension [70,74], when TEMPO was replaced by the more hydrophilic TEMPO-OH during the synthesis of PS homopolymers, significant differences appeared [69,73]. With TEMPO, the initiator efficiency was higher with KPS than with BPO whereas with TEMPO-OH, no such difference was observed.…”