Water-soluble complexes from random copolymer and oppositely charged surfactant. 1. Complexes of poly(ethylene glycol)-based cationic random copolymer and sodium dodecyl sulfate

In this study, we investigate the complex formation behavior of random copolymers (RCPs) of methoxy poly(ethylene glycol) monomethacrylate (MePEGMA) and (3-(methacryloylamino)propyl)trimethylammonium chloride (MAPTAC) with oppositely charged surfactant sodium dodecyl sulfate (SDS), which could be used as a potential system in the field of drug/gene delivery research. A series of copolymers from MePEGMA and cationic monomer MAPTAC were synthesized and characterized by H-1 NMR and static light scattering techniques. The complexation of SDS with synthesized cationic RCPs was investigated by turbidimetric titration, steady-state fluorescence, light scattering, particle size analysis and zeta-potential measurement. Studies revealed that these complexes are qualitatively similar to the polyion complex micelles or block ionomer complexes obtained from the block copolymers and oppositely charged surfactants. The complexes obtained appear to be micelle-like aggregates with a core formed by the dodecyl sulfate neutralized cationic unit of the polymer and a shell of threaded poly(ethylene glycol) units. The formation of hydrophobic domains occurs at an SDS concentration which is about 2 orders of magnitude lower than its critical micelle concentration. Copolymers with higher poly(ethylene glycol) content form hydrophobic domains at higher SDS concentration. The solution behavior of these complexes mainly depends on the composition of cationic and nonionic units present in the copolymers. Complexes with stoichiometric compositions of cationic units of the copolymer and SDS are electroneutral. The sizes of the complexes vary from 30 to 70 nm depending on the copolymer and the composition. The polarity index obtained from the pyrene fluorescence experiment shows that they are highly hydrated. Overall, these complexes represent an additional class of lyophilic colloids that could be used as a promising system in addressing various basic and practical problems in drug delivery challenges.