Influence of camphorsulfonic acid in nitroxide‐mediated styrene miniemulsion polymerization

Abstract

The rate-accelerating effects of camphorsulfonic acid (CSA) on nitroxidemediated styrene miniemulsion polymerization were studied. Polymerizations were initiated with benzoyl peroxide (BPO) as an initiator and mediated with either 2,2,6,6tetramethylpiperidinyloxy (TEMPO) or 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (OH-TEMPO). Although CSA has been used to accelerate the rate in bulk nitroxidemediated polymerizations, it has not been well studied in emulsion/miniemulsion. With dispersed systems, the effectiveness of CSA is likely to be affected by partitioning between the aqueous and organic phases. In styrene miniemulsion experiments performed over a range of conditions, the effect of adding CSA varied from negligible to significantly increasing the final conversion and molecular weight, depending on the nitroxide:BPO ratio. At a ratio of nitroxide:BPO ϭ 1.7, the effect of CSA addition is small, whereas the final conversion and molecular weight are dramatically enhanced by CSA addition when the nitroxide:BPO ratio is 3.6. CSA is most effective in enhancing the rate and molecular weight when the initial free-nitroxide concentration is higher. The magnitude of the rate and molecular weight enhancement was similar for TEMPO and OH-TEMPO despite their differences in water solubility.

Accelerated controlled radical polymerization of methacrylates

“…Our method is summarized in a stepwise fashion in the supporting information. The gravimetric approach has been used by many other researchers 57, 62–64…”

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

“…Georges and coworkers 148,149 found that the addition of CSA increases the consumption of TEMPO during the polymerization. A number of groups have used CSA to increase polymerization rates, 150,151 although no mechanism has been offered. During the polymerization, an equilibrium exists between the dormant polymer 42 and the growing polymer chain 43 and the mediating nitroxide (Scheme 12).…”

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

“…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]. Enright [7] first used a continuous tubular reactor apparatus and studied styrene miniemulsion polymerizations at 135uC using oligomers of polystyrene as a cosurfactant.…”