TEMPO Mediated Radical Emulsion Polymerization of Styrene by Stepwise and Semibatch Processes

Abstract

In the present study we carried out nitroxide mediated radical polymerizations (NMRP) of styrene in emulsion using 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) by stepwise and semibatch processes obtaining polystyrene (PS) with a dispersity (Đ) lower than 1.5 and average particle diameter (Dp) between 180 and 520 nm when methanol was used. Otherwise, when the polymerization was carried out in the absence of methanol, a bimodal particle size distribution (PSD) was obtained. This is attributed to the super‐swelling effect, which causes the particles to grow considerably and also to lower the nitroxide efficiency reducing chain formation and thus drastically reducing the particle nucleation. These polymerizations did not require a separate macroinitiator synthesis step, which represents an important simplification for further applications.

Effect of Chain Transfer to Polymer in Conventional and Living Emulsion Polymerization Process

“…In the present investigation, theoretical analysis is conducted, assuming an ideal ab initio emulsion polymerization both for conventional and living FRP. Emulsified systems provide the polymerization loci with huge surface area per unit volume, which enables one to conduct semibatch operation without suffered significantly by the slow diffusion of the added substances [14,15], which endows the process with additional operability. The present theoretical investigation is hoped to provide useful information, also for such advanced operation.…”

High solids TEMPO‐mediated radical semibatch emulsion polymerization of styrene

“…For the first two reactions, performed below the CMC of the surfactant, poor results were obtained, with low conversions (<50 %), very low N Eff (<0.1), low number of particles N p and relatively large dispersities (see Table ). The latex was stable during the reaction time but, once in storage (after a few minutes), a nitroxide‐rich surface layer appeared (identified as such due to its red color), attributed to the large D p and high concentration of St (low conversion), which caused the buoyant forces to become dominant and form an upper layer . Notice however that, in going from reaction RSC‐1 to 2 , a clear improvement in all the variables associated with latex stability and reaction control were apparent, due to the larger concentration of surfactant used in reaction RSC‐2 (closer to its CMC).…”

“…Finally, unlike previous reports in heterogeneous systems in which the molar ratio N/I has been set between 1.3 and 2.0, in this system such molar ratio was set at 0.77, which was established with the purpose of giving the primary radicals a higher probability of growing in the aqueous phase to a sufficient length to favor particle nucleation. Note that the presence of KPS ions lowers the CMC of the surfactant and also assists in stabilizing the formed particles .…”

“…González‐Blanco et al recently reported exploratory emulsion polymerizations by stepwise and semibatch processes using the bimolecular system TEMPO/KPS with solids content of ≈5 wt %. Controlled latexes of PS with conversions <40% (≈32 h), N Eff < 0.25, Đ < 1.5, and D p = 315 nm were obtained when methanol was used to suppress the superswelling of particles .…”

High Solids Hydroxy‐TEMPO Mediated Radical Semibatch Emulsion Polymerization of Styrene

“…After this work, many reports by ab initio, [12,17] stepwise, [16,18,19] seeded, [11,[18][19][20][21][22][23] and semibatch [19,24,25] emulsion polymerization processes appeared, using different nitroxides such as hydroxy-TEMPO, [12,20,21] amino-TEMPO, [12] TEMPO, [11][12][13][14][19][20][21]25] N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (SG1), [15] and the alkoxyamines BlocBuilder (BB) [16][17][18]22,24,26] and DiBlocBuilder (DiBB). [23,24] However, the majority of these processes presented some problems and drawbacks such as long seed-formation and…”