Fine-tuning of phase structures and thermoplasticity of polyelectrolyte-surfactant complexes: Copolymers of ionic monomers with N-alkylacrylamides

Copolymers of N-alkylacrylamide and ionic monomers which are complexed with surfactants represent a new type of highly ordered, solid mesomorphous materials where thermomechanical behavior as well as the phase structure can be adjusted to customer-specific demands. One synthetic route toward such complexes lies in a polymer-analogous amidation of poly(acrylic acid) with tetradecylamine to various extents and subsequent complexation with cetyltrimethylammonium counterions. The behavior of these copolymers was analyzed by scattering of synchrotron radiation as well as with DSC. In these experiments, a transition from a lamellar to two different types of modulated-lamellar phases with a different cubic packing of undulations is observed. In a second set of experiments, similar materials were made by copolymerization of N-octadecylacryl amide and sodium 2-acrylamido-2-methyl-1-propane-sulfonate and subsequent complexation of cetyltrimethylammonium counterions. The different copolymers in the series are characterized by a transition from a hexagonal to a disordered cubic morphology, depending on copolymer composition. In all cases, the degree of order of these complexes is very high, which allows some interesting applications of this new type of ordered, thermoplastic material.