RESUMO
The impact of the chain stiffness on physicochemical properties has been studied by chemical modification of xanthan under both ordered and disordered conformations. Corresponding rheological properties were studied and results showed that amphiphilic xanthan exhibited completely different behaviors depending on its conformation during modification. Xanthan, when modified under ordered conformation, exhibits similar behavior to non-modified one, only the chain relaxation being strongly slowed down. Therefore, the high stiffness of xanthan helices does not allow hydrophobic moieties to associate. Oppositely, xanthan modified under its disordered conformation displayed a chemical gel-like behavior without any relaxation of the chain within the studied frequency range nor with temperature, which is unexpected for this length of alkyl chains. These different viscoelastic properties can be correlated to the regioselectivity of the grafting; the latter can be controlled by the conformation of xanthan during modification, thus by the synthesis conditions.
