A novel type of positively charged copolymers, poly (2-methacryloyloxy ethyl trimethylammonium chloride-co-2-hydroxyethyl acrylate) (PDMCHEA) were synthesized via free-radical copolymerization. Positively charged nanofiltration membranes (PCNFMs) were made from PDMCHEAs copolymers via glutaraldehyde (GA) cross-linking method. Chemical structures and compositions of PDMCHEAs and PCNFMs changes with varying copolymerization ratio of DMC to HEA (R(DMC/HEA)), and were characterized by element analysis, viscosity measurements, attenuated total reflectance fourier transform infrared spectroscopy, field emission scanning electron microscope and atomic force microscopy, respectively. The optimum membrane preparation conditions: 1.5 wt% PDMCHEA, 0.3 wt% GA and cured at 50 degrees C for 3 h were obtained. Effects of charge density and molecular weight of PDMCHEAs on their membranes' nanofiltration performance were studied. It was found that the PCNFM3 (R(DMC/HEA) = 1.28) showed the best salt rejection and water flux, e.g. R(MgCl2) = 94.3%, J(MgCl2) = 19.1 L m(-2)h(-1), R(NaCl) = 60.7% and J(NaCl) =20.6 L m(-2) h(-1), respectively. PCNFM3 exhibited good separating capability and stability in its desalination process. Therefore, PDMCHEA is a promising material for fabricating PCNFMs with high performance in canons separation or recovery. (C) 2011 Elsevier B.V. All rights reserved.