Polyelectrolytes with various charge densities: Synthesis and characterization of diallyldimethylammonium chloride‐acrylamide copolymers

Abstract

AbstractThe synthesis of defined polyelectrolyte models by radical copolymerization of diallyldimethylammonium chloride (DADMAC, M1) and acrylamide (AAM, M2) in aqueous solution is impeded by a large difference of the reactivity ratios (r1 ≪ r2) leading to a strong conversion dependence of the copolymer composition. For the synthesis of normally distributed polyelectrolytes of the same molecular weight with various charge densities, a general algorithm based on a feeded polymerization with dosage of the more reactive monomer was therefore developed.Various copolymer compositions predictable by the Mayo‐Lewis equation and determined by chloride potentiometry were obtained. The sequence lengths distributions investigated by 13C NMR spectroscopy followed a Markov statistic of first order. The 13C NMR spectroscopy is shown as alternative method to gravimetry in determining reactivity ratios. The partial specific volumes and the refractive index increments of the copolymers correspond to the additivity principle. Further molecular and dynamic parameters are determined by membrane osmometry, static and dynamic light scattering, analytical ultracentrifugation, gel permeation chromatography, and viscometry. Monomodal molecular weight distributions, small polydispersities only for copolymers with high content of DADMAC are obtained at given comonomer and initiator concentration. The number‐average molecular weight is almost constant for a broad copolymer composition range.Rg‐M and [η]‐M relations could be established for practical use at high ionic strength, despite the various chemical compositions. Some indications for a higher stiffness of copolymers with high contents of DADMAC despite the shielding of the electrostatic interactions are, however, given. At low ionic strength the electrostatic interactions prevail. Their influence with increasing charge density is stronger on the Huggins constants (intermolecular interactions) than their effect on the intrinsic viscosities (intramolecular interactions).