Hemicellulosic polymers A and B were isolated from Populus gansuensis by extracting the chlorite-delignified residue with 10% KOH. Fractional precipitation of hemicellulose B by graded ethanol resulted in six subfractions varying in yield, molecular size distribution, and sugar composition. Macromolecular and more linear hemicellulosic polymers with higher yields were preferentially precipitated in relatively lower ethanol concentrations, while more branched and complex hemicellulosic polymers with lower molecular weights were obtained in relatively higher ethanol concentrations. Chemical and spectral evidence suggested that H30 subfraction obtained by 30% ethanol precipitation was assumed to be 4-O-methyl-D-glucurono-D-xylans, with 4-O-methyl-D-glucuronic acid linked to C-2 of (14)-beta-D-xylan. On average for every six D-xylopyranosyl residues, there is one 4-O-methyl-D-glucuronic acid group. Hemicellulosic subfraction H75 precipitated at the ethanol concentration of 75% was more branched, and presumed to be heterogeneous mixture of arabinoglucurnoxylan and galactoglucomannan. In addition, the thermal stability of the linear large molecular hemicellulosic subfraction H30 appeared higher than the branched subfraction H75. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012