Characterization of polyelectrolytes complexes based on N,N,N-trimethyl chitosan/heparin prepared at different pH conditions

N,N,N-trimethyl chitosan (TMC) was synthesized through the N-methylation of chitosan (CHT) and characterized by FTIR and H-1 NMR spectroscopy. Polyelectrolyte complexes (PECs) based on TMC and heparin (HP) were prepared at different pHs (5.8. 10 and 12) and characterized through FTIR spectroscopy, DSC and TGA curves and WAXS profiles. It was verified that the higher the pH of feed solution used for the PEC formation the higher is the thermal stability of PECs. Under basic conditions, the complexation between TMC and HP was more effective and alterations on WAXS profiles of PECs in relation to the precursor (TMC) were clearly observed. In addition, WAXS profiles show that the PEC crystallinity depends on the pH used for the complexation. These results are consistent with the FTIR, DSC, and TGA data. Due to the more intense electrostatic interactions, at higher pHs the unlike polymers chains (TMC and HP) are close enough to produce more stable PECs. (C) 2011 Elsevier Ltd. All rights reserved.