First Nitroxide-Mediated Controlled Free-Radical Polymerization of Acrylic Acid

Abstract

Controlled poly(acrylic acid) homopolymers were synthesized for the first time by direct nitroxide-mediated polymerization of acrylic acid. The polymerizations were performed in 1,4-dioxane solution at 120 °C, using an alkoxyamine initiator based on the N-tert-butyl-N-(1-diethyl phosphono-2,2dimethyl propyl) nitroxide, SG1. The kinetics were controlled by the addition of free nitroxide at the beginning of the polymerization and the optimal amount was 9 mol % with respect to the initiator. In this case, whatever the initiator concentration, all polymerizations exhibited the same rate and conversion reached 85-90% within 5 h. Although the rate constant of propagation of acrylic acid is very large, its reactivity is moderated by a low activation-deactivation equilibrium constant between active macroradicals and SG1-capped dormant chains. Various alkoxyamine concentrations were investigated to target different molar masses. At high initiator concentrations, the number-average molar mass, M n, increased linearly with monomer conversion and followed the theoretical values; the polydispersity indexes ranged between 1.3 and 1.5. At low initiator concentration (high target Mn), a deviation from linearity was observed in the Mn vs conversion plot and was clearly assigned to chain transfer to 1,4-dioxane. From these results, the best experimental conditions to obtain well-defined homopolymers with the minimum amount of dead chains were identified.

Synthesis of Stimuli-responsive, Water-soluble Poly[2-(dimethylamino)ethyl methacrylate/styrene] Statistical Copolymers by Nitroxide Mediated Polymerization

“…As a result, SG1-based initiators can be activated at lower temperatures and allow controlled polymerizations of a wider range of monomers, such as methacrylates, compared to TEMPO. However, when polymerizing non-styrenic monomers using BlocBuilder, additional SG1 nitroxide was required to further reduce polymerization rate and produce well-defined copolymers [28,[47][48][49].…”

Analytical strategy for the molecular weight determination of random copolymers of poly(methyl methacrylate) and poly(methacrylic acid)

“…However, before examining random MAA-MMA copolymers, the derivatization procedure was first tested on PMAA homopolymers, with an H atom as both end-groups and various sizes in the 1200 to 6600 Da mass range, using the protocol described by Couvreur et al [34]. Before derivatization, PMAA homopolymers gave rise to complex mass spectra in negative mode MALDI (using sinapic acid as the matrix), as exemplified in Figure 1a for PMAA1700.…”

“…The methylation procedure was derived from a published protocol [34] and is briefly described hereafter. MAA-MMA copolymers or PMAA homopolymers (50 mg) were first dissolved in a methanol/water mixture (19:1, vol/vol) and stirred at moderate speed for 2 h. Trimethylsilyldiazomethane was then added dropwise until the polymer solution became yellow, indicating the methylation agent was in excess.…”

“…Sample derivatization is a technique that has been widely used to enable gas chromatography analysis of small polar compounds. Methylation was also reported for PMAA homopolymers and allowed the accuracy of molecular weight parameters as determined by SEC to be improved [34], or signals obtained in MALDI to be enhanced and simplified [35]. This strategy has been successfully applied here to random MAA-MMA copolymers to enable the use of MALDI and PGSE for the determination of M w parameters of the so-obtained PMMA homopolymers.…”

Synthesis and quaternization of nitroxide-terminated poly(4-vinylpyridine-co-acrylonitrile) macroinitiators and related diblock copolymers

“…A quasiliving polymerization takes place at elevated temperatures (usually above 100 o C) in mixtures containing monomer, a thermal initiator [(dibenzoyl peroxide, 2,2΄-azobis(isobutyronitrile)] and a nitroxide stable radical. Instead of the conjuction of thermal initiator with nitroxide, an alkoxyamine-based unimolecular initiator carrying both a latent initiating group and nitroxide in the 1:1 mole ratio can be used [10,15]. Some monomers and monomer pairs (styrene, styrene maleimide or styrene Nsubstituted maleimide derivative) polymerize in the quasiliving manner even without any added initiator, only in the presence of nitroxide [5,16,17].…”