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.

中文翻译：

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黄原胶在有序和无序状态下的化学修饰：调节理化性质的开放途径

通过在有序和无序构象下对黄原进行化学修饰，研究了链刚度对理化性质的影响。研究了相应的流变性质，结果表明，两亲性黄原胶在改性过程中表现出完全不同的行为，这取决于其构象。当在有序构象下进行修饰时，黄原胶表现出与未修饰的相似的行为，仅链弛豫被大大减慢。因此，黄原体螺旋的高刚度不允许疏水部分缔合。相反，在其无序构象下修饰的黄原胶表现出化学凝胶样的行为，在研究的频率范围内或温度范围内，链没有任何松弛，这对于该烷基链的长度而言是出乎意料的。这些不同的粘弹性能可以与接枝的区域选择性相关。后者可以通过在修饰过程中黄原胶的构象来控制，因此可以通过合成条件来控制。