The solution polymerization of acrylamide (AM) on cationic guar gum (CGG) under nitrogen atmosphere using ceric ammonium sulfate (CAS) as the initiator has been realized. The effects of monomer concentration and reaction temperature on grafting conversion, grafting ratio, and grafting efficiency (GE) have been studied. The optimal conditions such as 1.3 mol of AM monomer and 2.2 x 10(-4) Mol of CAS have been adopted to produce grafted copolymer (CGGI-g-PAM) of high GE of more than 95% at 10 degrees C. The rates of polymerization (R-p) and rates of graft copolymerization (R-g) are enhanced with increase in temperature (< 35 degrees C). The R-p is enhanced from 0.43 x 10(-4) mol L-1 s(-1) for GG-g-PAM to 2.53 x 10(-4) mol L-1 s(-1) for CGG1-g-PAM (CGG1, degree of substitute (DS) = 0.007), and R-g from 0.42 x 10(-4) to 2.00 x 10(-4) mol L-1 s(-1) at 10 degrees C. The apparent activation energy is decreased from 32.27 kJ rnol(-1) for GG-g-PAM to 8.09 kJ mol(-1) for CGGI-g-PAM, which indicates CGG has higher reactivity than unmodified GG ranging from 10 to 50 degrees C. Increase of DS of CGG will lead to slow improvement of the polymerization rates and a hypothetical mechanism is put forward. The grafted copolymer has been characterized by infrared spectroscopy, thermal analysis, and scanning electron microscopy. (c) 2007 Wiley Periodicals, Inc.