Solution properties of a hydrophobically associating polyacrylamide and its polyelectrolyte derivatives determined by light scattering, small angle x-ray scattering and viscometry

Abstract

Uma poliacrilamida hidrofobicamente modificada e dois dos seus derivados parcialmente hidrolisados, contendo grupos hidrofóbicos e carboxila, foram preparados por polimerização micelar e pós-hidrólise. A massa molar, o segundo coeficiente do virial e o raio de giração foram determinados por espalhamento de luz estático (SLS). O espalhamento de luz dinâmico (DLS) e o espalhamento de raios-X a baixos ângulos (SAXS) foram utilizados respectivamente para determinar a formação de agregados e o tipo de empacotamento das cadeias em regime semi-diluído. O comportamento das soluções, em regime diluído e semi-diluído foi estudado por viscosimetria e reologia. A poliacrilamida modificada hidrofobicamente apresentou tendência à formação de agregados devido aos grupos hidrofóbicos, mas essa agregação não foi suficiente para aumentar a viscosidade aparente. Embora os derivados parcialmente hidrolisados não apresentassem a mesma tendência para agregação, eles apresentaram um comportamento anisotrópico devido à introdução de densidade de carga sobre a cadeia polimérica, a qual levou a uma conformação mais alongada da macromolécula e maior viscosidade.A hydrophobically-modified polyacrylamide and two partially hydrolyzed derivatives containing hydrophobic and carboxylic groups were prepared by micellar polymerization and posthydrolysis. The molecular weight, second virial coefficient and radius of gyration were determined by static light scattering (SLS). Dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) were employed to determine the aggregate formation and type of chain packing in the semidilute regime, respectively. The behavior of solutions in dilute and semidilute regimes was also studied by viscometry and rheology. The hydrophobically-modified polyacrylamide showed a tendency to form aggregates due to the hydrophobic groups, but not enough to increase apparent viscosity. The partially hydrolyzed derivatives did not show the same aggregate-forming tendency. Rather, they exhibited anisotropic behavior, due to the charge density introduced into the polymer chain, which led to a more elongated macromolecular conformation and higher viscosity.

Aqueous solutions of HEC and hmHEC: effects of molecular mass versus hydrophobic associations on hydrodynamic and thermodynamic parameters

“…Simon et al (2003) observed that the K H for amphiphilic derivatives of carboxymethyl pullulans increased with increasing degree of hydrophobic modification. This trend has also been reported for hydrophobically modified derivatives of dextran (Rotureau et al 2006), polyacrylamide (Maia et al 2011) and carboxymethylcellulose (CharpentierValenza et al 2005). These studies attributed the increase in K H to increasing polymer-polymer interaction and decreasing polymer-solvent interaction, which could also be referred to as the formation of a reversible network by supramolecular aggregation.…”

“…Although this is expected owing to the lower molecular mass of hmHEC compared to that of the HEC, the presence of hydrophobic associations ) and the empirical constants obtained from Huggins, Kraemer and Schulz-Blaschke equations for all set A and B polymers and the concentration c NL at which the corresponding data exhibits a deviation from Huggins equation also cause the collapse of the coil, making it more compact and resulting into a lower value of intrinsic viscosity. This phenomenon has been reported for the hydrophobically modified derivatives of many polymers such as dextran (Rotureau et al 2006;Durand 2007a, b), carboxymethyl cellulose (CharpentierValenza et al 2005), polyacrylamide (Maia et al 2011) and hmHEC (Maestro et al 2002a). However, for set B polymers the intrinsic viscosity values of amphiphilic derivatives are higher than that of the corresponding non-associative derivative.…”

“…Among all the extrapolation methods describe above, the Fedors equation has been reported within the past few years to be applicable for many polymers and to a much wider range of concentration with good linearity compared to other equations (Rotureau et al 2006;Maia et al 2011;Pavlov et al 2006;Durand 2007b).…”

“…As an alternative approach, many different empirical methods (i.e. Martin, Schulz-Blaschke, Fedors, Fuoss and Heller) have been used to calculate the intrinsic viscosity of associative derivatives of polymers such as dextran (Rotureau et al 2006;Durand 2007b), polyacrylamide (Maia et al 2011;Ma et al 2003) and cationic polyelectrolytes (Dragan and Ghimici 2001). In most cases, the use of alternative empirical methods (especially Fedors equation) has not only provided a more accurate prediction of the viscometric behavior at a much wider concentration range compared to that of Huggins, but the knowledge of the empirical parameters obtained from these relationships has been helpful for interpreting the nature of the polymersolvent interaction.…”

“…Numerous studies have reported the reduction of intrinsic viscosity in associative polymers as a result of intramolecular associations, e.g. hydrophobic derivatives of polymer such as dextran (Rotureau et al 2006;Durand 2007a, b), carboxymethyl cellulose (Charpentier-Valenza et al 2005), polyacrylamide (Maia et al 2011) and HEC (Maestro et al 2002a). The degree of hydrophobic modification has been sufficiently high in all the above studies to cause the polymer coil to have a lower size compared to the coil of its corresponding nonassociative derivative with similar molecular mass (due to a denser packing of chains within a coil) even though the coil was likely to be an aggregate of more than one polymer chains.…”