Dilute solution behaviour of progressively hydrolyzed polyacrylamide in water–N, N dimethylformamide mixtures

Abstract

The intrinsic viscosities [η’s] of anionic (hydrolyzed; low and high carboxyl content) and nonionic polyacrylamide (unhydrolyzed) were measured in water–N, N dimethylformamide mixtures at various temperatures. Non-polyelectrolyte behavior of low carboxyl content polyacrylamide was observed in mixed solvent system. The plots of [η] vs. solvent composition in a mixed solvent system pass through minima for both high as well as low carboxyl content polymers but through a maximum for nonionic polyacrylamide. Observed minimum for charged polymers may be attributed to the loss of polymer sites available to interact with solvent for H-bonding interaction between neighboring amide and the acid groups. The maximum for nonionic polymer at the particular solvent composition arises for the most powerful cosolvent effect. Existence of two antagonistic effects is apparent in [η] values of nonionic polymer at various temperatures. Huggins constant (K_H) also indicates a significant variation of cosolvency as a function of solvent composition. Activation parameters of viscous flow were calculated using Frenkel–Eyring equation. The volume related parameter and the shape factor were also computed. Shape factor data indicate that polymer molecules are more or less rigid spheres and are not affected by temperature and composition of solvent.

Introduction

Water-soluble polymers find a very broad range of industrial applications. Acrylamide based polymers are widely used as flocculants, rheology control agents, and additives [1], [2], [3]. Paper manufacturing [4], [5], mining [6], [7] and water treatment [8] processes are among the many fields that benefit from the use of acrylamide-based polymers. In solution phase, progressively hydrolyzed polyacrylamide (PAM) develops varied charge densities on the polymer backbone and as such, solution behaviour of the polymer is modified. Hydrolysis of amide groups in the alkaline condition, adsorption of nonionic [NPAM] [9], [10], [11], [12], anionic [13], [14], [15] and cationic [16], [17] types of PAM on charged surfaces at different pH media are documented in literature [18], [19]. If hydrolyzed-PAM is dissolved in water [20], it behaves like weak polyelectrolyte with charged COO⁻ on the backbone. In this charged PAM, relative dissociation of the ionic groups is a function of solvent polarity and the distribution and alignment of the charged dipoles along the chain are expected to play decisive role on the final state of conformation of the polymer chain [18]. Partially hydrolyzed PAM is thus expected to develop fascinating solution behavior especially in aqueous–non-aqueous mixed solvents. Although some studies on solution viscosity properties of PAM in water are available in the literature, similar studies of hydrolyzed PAM in other solvents or cosolvents are little [21], [22], [23], [24], [25], [26], [27]. The effect of hydrodynamic field and the degree of hydrolysis on apparent conformation of hydrolyzed PAM has been discussed [28]. In our previous publications, we have reported the synthesis [29], [30], [31] and solution properties [32] of high molecular weight nonionic PAM. In continuation to our studies on physicochemical behavior of water-soluble synthetic polymers, present paper reports the variation of [η], activation entropy and activation enthalpy $(\mathrm{\Delta }{S}_{\mathrm{vis}}^{\#}\mathrm{and}\mathrm{\Delta }{H}_{\mathrm{vis}}^{\#})$, and volume related parameter (V_E), and the shape factor (ν) of both ionic and nonionic PAM with solvent composition in water–DMF system. While DMF is a poor solvent, water–DMF mixtures act as a cosolvent in certain proportions.