Characterization of cationic copolymers by capillary electrophoresis using indirect UV detection and contactless conductivity detection.

For many industrial applications, the combination of two different monomers in statistical or diblock copolymers enhances the properties of the corresponding polymer. However, during the polymerization reaction, homopolymers might be formed and can influence the properties for the applications. Consequently, the separation and the quantification of the homopolymers contained in copolymer samples are crucial. In addition, the charge density distribution of the statistical copolymer is an important characteristic for the applications. The purpose of this work was to study the characterization of a statistical copolymer of acrylic acid (AA) and diallyldimethyl ammonium chloride (DADMAC) by capillary electrophoresis (CE) in acidic conditions (cationic copolymers). For that purpose, a free solution electrophoretic separation was carried out according to the charge rate (chemical composition) independently of the molar mass. The second objective was to compare contactless conductivity detection and indirect UV absorbance modes for the quantification of DADMAC homopolymers present in copolymer samples. Different coated capillaries based on neutral or positively charged modification were also compared. The comparison of indirect absorbance UV and contactless conductimetric detection demonstrated that both detection modes can be used for a complete CE characterization of non-UV absorbing PAA-DADMAC copolymers.

Characterization of copolymer latexes by capillary electrophoresis.

Latexes are widely used for industrial applications, including decorative paints, binders for the papermaking industry, and drilling fluids for oil-field applications. In this work, the interest of capillary zone electrophoresis (CE) for the characterization of hydrophobic block copolymer latexes obtained by the conventional emulsion polymerization technique consisting of a core of polystyrene (PS) surrounded by a layer of poly(ethyl acrylate) (PEA) has been investigated. The PEA part of the copolymer can be partially hydrolyzed in poly(acrylic acid) (PAA) leading to PS-PEA-AA water-soluble amphiphilic copolymer having high viscosifying properties. The main purpose of this work was to evaluate the potential of CE for the characterization of the latexes at the different stages of the synthesis (PS core, PS-PEA diblock latex, and hydrolyzed PS-PEA-AA gel). The main analytical issues were to state (i) if there was free PS or PEA homopolymer latexes in the PS-PEA latex sample and (ii) if there was free PS, PEA, PS-PEA latexes, or free PAA chains in the PS-PEA-AA gel. Within this scope, this work describes the optimization of the selectivity of the separation between the different species (PS, PEA particles in the not hydrolyzed diblock latex and PS, PEA, PS-PEA particles as well as the polymer PAA chains in the PS-PEA-AA diblock gel sample obtained by latter latex hydrolysis). For that purpose, several experimental parameters were investigated such as pH and ionic strength of the background electrolyte (BGE) or the concentration of neutral surfactant added in the BGE. A challenging issue was to overcome the high viscosity of the PS-PEA-AA gel. This was resolved by the addition of 10 mM neutral surfactant in the gel sample and in the BGE. Finally, it is demonstrated that, within the detection limits, CE is a suitable analytical tool for controlling and monitoring the syntheses of these latexes and for intrinsically characterizing the distribution in charge density of the final PS-PEA-AA gel at different hydrolysis rates.

Reconciling low- and high-salt solution behavior of sulfobetaine polyzwitterions.

We investigate the water-solubility upon salt additions, of homogeneous families of sulfobetaine-based polyzwitterions. These polymers bear both positive ammonium, and negative sulfonate charges on each monomer and as a result present an upper critical solution temperature (UCST) in the 0-100 degrees C temperature range. Two chemistries are investigated, with either a carboxylate-carrying function (SPE) or an amido-carrying one (SPP). In agreement with the literature published on pSPEs, we find that an addition of simple salts improves the water-solubility of pSPEs, as well as that of pSPPs, yet only once a threshold concentration of added salt has been reached in the solution. We verify using scaling arguments that the onset of solubility promotion, corresponds exactly to the complete screening of the attraction between positive and negative charges inside a polyzwitterionic coil. On the contrary, for salt concentrations smaller than the threshold concentration, we observe that an addition of salt can be adverse to the solubility of polyzwitterions, depending on the degree of polymerization, the type of salt, and the type of zwitterionic motive. Thanks to zeta-potential measurements and systematic variations of these three parameters, we demonstrate, in agreement with theoretical prediction, that this molecular weight-dependent enhanced solubility at small salt concentrations is due to charge asymmetry resulting from partial hydrolysis, combined with specific interactions between salts and zwitterion constituents, evidencing the complexity of the solution behavior of these macromolecules. We thereby reconcile the different behaviors in the domains of low- and high-salinity.