Solubilisation of organic compounds of different polarity by interpolyelectrolyte complexes based on copolymer micelles
When two oppositely charged polyelectrolytes are mixed, the spontaneous formation of interpolyelectrolyte complexes (IPEC) takes place. As different polyelectrolytes with various molecular architectures can be combined, the structures formed are rich in their variety as well as properties. In this work, the molecular architecture of polyanions was designed through the atom transfer radical polymerization (ATRP). IPEC of oppositely charged polydiallyldimethylammonium chloride (PDADMAC) and sodium polyacrylate (NaPA) were studied under variation of the Mw of PDADMAC. The effect of the hydrophobic modification of NaPA with dodecyl alkyl side chains was studied by a detailed characterization of the phase behaviour and by the use of various methods such as light (LS) and neutron scattering (SANS) and zeta potential. It was found that complexes are formed with radii of gyration of ∼ 30-40 nm, and become somewhat smaller with increasing length of the PDADMAC chain. The overall structure of the IPECs was found to be largely determined by the presence of the hydrophobic modification of the NaPA. Micellar IPEC of PDADMAC and hydrophobically modified sodium polyacrylate and polymethacrylate HM-NaP(M)A of varying degree of polymerization, hydrophobic modification and the length of the hydrophobic side chain were successfully used in solubilisation of pharmaceutical compounds of different polarity. It was shown that the system is responsive to the change in the reaction media, opening the opportunity of releasing a payload by means of changing the ionic strength of the system. Moreover, the solubilisation capacity can be easily tuned via the hydrophobic modification. A model system of polyelectrolyte and surfactant complexes (PESC) based on sodium dodecyl sulfate (SDS) and PDADMAC was investigated. Prepared PESC formed a distinct core and shell structure, without any significant change in the system viscosity. Incorporation of relatively small amounts of n-dodecanol cosurfactant, however, resulted in a striking increase of the PESC viscosity. This was attributed to the enhanced binding of PDADMAC chains and hence slowed chain dynamics, as was confirmed by SANS and by neutron spin-echo (NSE). Higher concentrations of n-dodecanol resulted in a decrease of a solubilisation capacity of formed PESC with solubilised fenofibrate. Complexes of positively charged oil in water microemulsion (ME) and copolymers of polyethylene glycol-block- polymethacrylic acid sodium salt (PEG-NaPMA) of varying chain length were investigated (PEMEC). The incorporation of a water-soluble PEG block allowed the formation of macroscopically homogeneous complexes at a charge neutrality. It was found that for the longer polyanion chain, formed complexes at a given Z are bigger and can incorporate by up to 2 times more ME droplets. Increase of the surface charge of ME also results in the formation of much bigger aggregates.
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