The influence of the type of substituents on the polymer dynamics of different regioselective 2-O-esters of starch using dielectric spectroscopy

The dielectric relaxation spectra of different regioselective 2-O-acyl-esters of amylomaize starch with a degree of substitution DS = 1 were measured in an extended temperature (-135 to 0 degreesC) and frequency range (0.01 Hz to 3 MHz). For all starch esters, two relaxation processes were found, which are from the type of a secondary relaxation (constant activation energy). One process can be assigned to the local backbone motion of the polymer and the other one with the ester side group motion in position C2 at the anhydro glucose unit. The dynamic parameters of both relaxations were determined and compared. The double bond in the crotonoyl-ester side group has a little influence on both the segmental and the side group motion in relation to the butanoyl-ester. The bulky benzoyl-ester side group shows an inverse influence on the local chain dynamics than the alkyl-ester side group. (C) 2001 Published by Elsevier Science Ltd.