Polyelectrolyte Complex Nanoparticles from N-Carboxyethylchitosan and Polycationic Double Hydrophilic Diblock Copolymer

For the first time, the polyelectrolyte complex (PEC) formation tool was used for preparation of core-shell nanoparticles form the natural polyampholyte N-carboxyethylchitosan (CECh) and weak polycationic (protonated) polyoxyethylene-b-poly[2-(dimethyl-amino)ethyl methacrylate] (POE-b-PDMAEMA) diblock copolymers. The performed dynamic light scattering analyses revealed that nanoparticles with a PEC core and a POE shell could be formed at mixing ratio between the oppositely charged groups equal to 1/1 depending on CECh molar mass, polymerization degree of PDMAEMA block and ionic strength. The results were confirmed by the performed AFM and cryo-TEM analyses. When high molar mass CECh was used, core-shell nanoparticles were obtained with the diblock copolymer of the shortest PDMAEMA block at ionic strength (I) of 0.01. At ionic strength value close to the physiological one (I = 0.1) secondary aggregation occurred. Spherical nanoparticles at I = 0.1 were obtained upon lowering the CECh molar mass. Depending on the polymer partners and medium parameters the size of the obtained particles varied from 60 to 600 nm. The X-ray photoelectron spectra evidenced the hydrophilic POE-block shell-coacervate CECh/PDMAEMA-block core structure. The nanoparticles are stable in a rather narrow pH range around 7.0, thus revealing the high pH-sensitivity of the obtained core-shell particles.