Nitroxide mediated living radical polymerization in miniemulsion

Abstract

The introduction of the aqueous phase into a living radical polymerization increases the complexity of the kinetics by creating the possibility of species partitioning between the aqueous and organic phases, and introducing aqueous phase reactions which could play a significant role particularly in chain initiation and/or particle nucleation. We have conducted a series of styrene miniemulsion polymerizations in which the solubility of initiator and nitroxide have been systematically varied. Experiments were run using either water‐soluble (potassium persulphate) or oil‐soluble (benzoyl peroxide) initiator, and either TEMPO or 4‐hydroxy‐TEMPO. These two nitroxides vary considerably in their water solubility. The effects of initiator and nitroxide solubility in water on conversion‐time behaviour, molecular weight and initiator efficiency are presented.

Controlled/living photopolymerization of methyl methacrylate in miniemulsion mediated by HTEMPO

“…Pan et al [4] used TEMPO-terminated oligomers of polystyrene as a macroinitiator to initiate the miniemulsion polymerization of styrene at 125uC and found that the molecular weight distribution of the PS products was not narrow. Cunningham [5] compared miniemulsion polymerization of styrene in TEMPO/ benzoyl peroxide (BPO), TEMPO/potassium persulfate (KPS), 4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy (HTEMPO)/BPO and HTEMPO/KPS four different systems. They also studied the influence of the rateaccelerating additive camphorsulfonic acid (CSA) in heterogeneous styrene miniemulsion polymerizations with TEMPO/BPO and HTEMPO/BPO systems, respectively [6].…”

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 .…”

Incubation period in the 2,2,4,4‐tetramethyl‐1‐piperidinyloxy‐mediated thermal autopolymerization of styrene: Kinetics and simulations

“…From a practical point of view, although it has been experimentally found that a ratio of TEMPO to the initiator of about 1.3 generally works well in bimolecular bulk NMP,12 the presence and length of an induction period will be rather sensitive to the ratio used, as any shortage of the initiator will generate and increase this period. Also, bimolecular systems may present additional complex behavior, especially in heterogeneous reactions,35 which may be difficult to interpret. Clearly, a better understanding of the induction period is needed.…”