Polymeric biosurfactants were prepared by the transesterification reaction between rapeseed oil triacyl glycerides and carboxymethylcellulose (CMC). The reaction was performed in H(2)O/N,N dimethylformamide (DMF) with potassium laurate as catalyst at various reaction conditions using microwave radiation as heating source. The structural features of the obtained water-soluble CMC derivatives were characterized Fourier-transform infrared (FT-IR) spectroscopy and their behavior in dilute aqueous solutions was investigated by surface activity measurements, viscometry and with a polarity probe, the Coomassie Brilliant Blue dye. All derivatives showed a very low esterification extent and moderate surface tension lowering effect. Nevertheless, they exhibited significant emulsifying efficiency comparable to that of the synthetic surfactant, Tween 20. They establish hydrophobic associations in bulk solution while adsorbing on the air/water interface. The presence of hydrophobic substituents in CMC molecules enhanced the hydrophobicity resulting in higher emulsion stability than produced by Tween 20. The results suggested that suitable polymeric biosurfactants applicable as emulsifying agents can be prepared from CMC under microwave heating at low microwave power and reaction times in the range of few minutes, what represents a great advantage in comparison with transesterification reactions lasting up to 6 h at conventional heating. POLYM. ENG. SCI., 51: 1476-1483, 2011. (C) 2011 Society of Plastics Engineers