SEC Analysis of Poly(Acrylic Acid) and Poly(Methacrylic Acid)

Abstract

The accurate characterization of molar-mass distributions of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) by size-exclusion chromatography (SEC) is addressed. Two methods are employed: direct aqueous-phase SEC on P(M)AA and THF-based SEC after esterifi cation of P(M)AA to the associated methyl esters, P(M)MA. P(M)AA calibration standards, P(M)AA samples prepared by pulsed-laser polymerization (PLP), and PAA samples prepared by reversible addition-fragmentation chain transfer (RAFT) are characterized in a joint initiative of seven laboratories, with satisfactory agreement achieved between the institutions. Both SEC methods provide reliable results for PMAA. In the case of PAA, close agreement between the two SEC methods is only observed for samples prepared by RAFT polymerization with weightaverage molar mass between 80 000 and 145 000 g mol −1 and for standards with peak molar masses below 20 000 g mol −1 . For standards with higher molar masses and for PLP-prepared PAA, the values from THF-based SEC are as much as 40% below the molar masses determined by aqueous-phase SEC. This discrepancy may be due to branching or degradation of branched PAA during methylation. While both SEC methods can be recommended for PMAA, aqueous-phase SEC should be used for molar-mass analysis of PAA unless the sample is not branched.

Modular, Flexible, and Continuous Plant for Radical Polymerization in Aqueous Solution

“…The experimental devices combined refractive index and multiangle light scattering detectors, and thus provided absolute molar mass distributions. The eluent was an aqueous solution with a high ionic strength because of polyelectrolyte character of polymers …”

Pulsed laser studies of cationic reactive surfactant radical propagation kinetics

“…The IUPAC subcommittee on "Modeling of Polymerization Kinetics and Processes" has benchmarked Arrhenius parameters that describe family behavior for the bulk kp of methyl methacrylate (MMA) and other alkyl ester methacrylates, 25,26 where an increase in linear length of the ester side chain correlates with an increase in bulk kp. However, the study of aqueous propagation kinetics is not as straightforward due to the added complexities of aqueous phase SEC analysis, 27 and significant solvent effects on kp. 28 For example, entropic reasons dictate that the kp for non-ionized water-soluble monomers, such as methacrylic acid (MAA), increases sharply towards low monomer concentrations, [29][30][31][32][33][34][35][36] while the activation energy (EA) of partially and fully ionized MAA decreases towards higher monomer concentrations corresponding to greater ionic strengths.…”

Cellular Response to Linear and Branched Poly(acrylic acid)

“…Concentrations are expressed in mmol · L −1 of sodium acrylate units. The concentration of PNaA chains would also be relevant but it cannot be determined accurately because of the uncertainty of the molar mass values determined by SEC in the case of branched PNaA, as shown by an IUPAC working party …”