Styrene/Acrylic Acid Random Copolymers Synthesized by Nitroxide-Mediated Polymerization: Effect of Free Nitroxide on Kinetics and Copolymer Composition

Abstract

Styrene/acrylic acid (S/AA) mixtures were copolymerized in concentrated 50 wt % 1,4-dioxane solutions at 120 °C at two ratios of additional free nitroxide mediator, N,N-tert-butyl-N-[1′-diethylphosphono-2,2′-dimethylpropyl] nitroxide (SG1), relative to 2-[N-tert-butyl-2,2-(dimethylpropyl)aminooxy]propionic acid (BlocBuilder, Arkema) alkoxyamine unimolecular initiator (4.5 and 9 mol % [SG1]/[BlocBuilder]). Without SG1 at initial acrylic acid monomer feed concentrations f AA,0 > 40 mol %, the apparent rate constants increased sharply, noticeable exotherms were observed, and polydispersities increased from 1.20 at f AA,0 ) 0 mol % to 1.48 at f AA,0 ) 80 mol %. With 4.5 mol % [SG1]/[BlocBuilder], polymerization rates were slower and not as strongly affected by f AA,0 although exotherms were still noticeable at high f AA,0 . Polydispersities remained ∼1.3 and only increased to >1.4 at high conversions for f AA,0 ) 80 mol %. Exotherms were rendered nearly negligible when 9 mol % [SG1]/[BlocBuilder] was used, leading to copolymers with much narrower molecular weight distributions and k p K values for comonomer mixtures bracketed between those of styrene and acrylic acid homopolymerizations at 120 °C (k p ) propagation rate constant, K ) equilibrium constant). Copolymer reactivity ratios estimated for samples produced using 9 mol % [SG1]/[BlocBuilder] by nonlinear least-squares minimization were r AA ) 0.25 ( 0.11 and r S ) 0.93 ( 0.37, in agreement with previous literature.

Poly(methacrylic acid-ran-2-vinylpyridine) Statistical Copolymer and Derived Dual pH-Temperature Responsive Block Copolymers by Nitroxide-Mediated Polymerization

“…Plots of <k p > <K> were typical of methacrylic ester/styrenic copolymerizations where a massive increase in this parameter is only witnessed for very rich methacrylate compositions (>90 mol% in the initial mixture). This same trend has been widely reported by Charleux and co-workers and others [45][46][47][48][49][50]. It should be noted here that additional free nitroxide was not required to control the methacrylate-rich compositions.…”

Copper(0)‐Mediated Living Radical Polymerization of Methyl Methacrylate in a Non‐polar Solvent

“…This is analogous to the effect seen in NMP, where the addition of a small amount of free nitroxide shifts the equilibrium between dormant and active chains. [29,30] This increases the time that the propagating macroradical spends in the dormant state, thus reducing the propagation rate and giving a more controlled polymerization. One of the main benefits of LRP techniques is the ability to form block copolymers.…”

Boron Subphthalocyanine Polymers by Facile Coupling to Poly(acrylic acid‐ran‐styrene) Copolymers Synthesized by Nitroxide‐Mediated Polymerization and the Associated Problems with Autoinitiation

“…The homopolymers and/or copolymers are usually characterized by a relatively narrow molecular weight distribution (PDI < 1.3). While the use of second‐generation SFRs such as {tert‐butyl[1‐(diethoxyphosphoryl)‐2,2‐dimethylpropyl] amino} nitroxide(SG1, Figure 1) has allowed the controlled homopolymerization of a variety of poly(acrylate)s including poly(AA)23–25 and its protected form, poly( tert‐ butyl acrylate) (poly(tBA)) 26–28. TEMPO was chosen for this study as it is commercially available, relatively inexpensive and is the prototypical SFR for use with styrenics.…”