Optimizing nitroxide-mediated miniemulsion polymerization processes

Abstract

Living/controlled radical polymerizations provide significant advantages in the control of polymer resin microstructure compared to conventional radical polymerization. Advances in our ability to tailor polymer microstructure will enable improvements in coatings properties and possibly new applications of coating technologies. Adapting living radical polymerizations to heterogeneous media such as aqueous-based miniemulsion polymerization presents several challenges related to maintaining the livingness (the fraction of chains that are still "living" at the end of polymerization) of the polymer chains and also developing a commercially viable process. We have studied the nitroxide-mediated polymerization of styrene in miniemulsion, with the intent of maintaining a high degree of livingness by balancing the rates of biradical termination and disproportionation. We can now achieve >95% monomer conversion in less than three hours, while maintaining polydispersities ~1.3. Monomer conversion can be dramatically increased from about 60-95% by changing the concentration of sodium dodecylbenzenesulfonate (SDBS) surfactant. Conversions in Dowfax 8390 stabilized miniemulsions showed no comparable dependency. Reasons for this potentially commercially important effect are under investigation.

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

“…A potentially complicating factor is that DOWFAX 8390 was used as a surfactant by Pan et al [23,24] and Cunningham et al have reported that the R p of S miniemulsion polymerization using PS-T depends strongly on the DBS concentration (for similar particle size distributions) for reasons that are currently unclear. [25] The number of propagating radicals per particle (n) was calculated from Equation (2):…”

Particle Size Effects in TEMPO‐Mediated Radical Polymerization of Styrene in Aqueous 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 . [29] Pan et al [31] reported that in the TEMPO-mediated thermal miniemulsion polymerization of S at 125 8C, the initial R p was approx.…”

Controlled/Living Radical Polymerization in Aqueous Miniemulsion

“…However, PDI were slightly higher (~1.4-1.6) than those obtained under classical experimental conditions. Preformed molecular oil-soluble alkoxyamine, either based on TEMPO and derivatives [83,87,88] or SGI (MONAMS) [89][90][91][92], have been used for the polymerization of styrene and n-butyl acrylate in aqueous miniemulsion. A mathematical model developed by Ma et al predicted that under TEMPO-based molecular alkoxyamine initiation, the living fraction of the polymer should decrease with monomer conversion and the PDI should increase when reaching high monomer conversion [88].…”

“…A mathematical model developed by Ma et al predicted that under TEMPO-based molecular alkoxyamine initiation, the living fraction of the polymer should decrease with monomer conversion and the PDI should increase when reaching high monomer conversion [88]. However, for the polymerization of styrene initiated by the BST-TEMPO alkoxyamine (Figure 7.9a), adequate experimental conditions led to narrow molar mass distributions (PDI ~1.3) and high monomer conversions [83]. In contrast, with nBA in conjunction with ascorbic acid at 135°C [87], a higher PDI was obtained (-1.6 at 60% monomer conversion) compared to previous results involving the TIPNO-OH nitroxide.…”