AbstractA series of (cellulose oligo‐oxymethylene ether) acylates (COAs) are characterized by the presence of the micro‐Brownian motion of the side chain (β process) which appears separately from that of the main chain (α process). Both the alpha; and β processes are largely affected by the kind of acyl groups introduced in the side chain. To clarify the effect of the acyl group on these processes, we investigated the dynamic mechanical properties of newly prepared COAs with acyl side chain, bulky in chemical structure (iso‐butyrate, privalate, and benzoate) in relation to those for COAs with linear acyl side chain (acetate, butyrate, and valerate). By substituting bulky acyl isomer for linear acyl group in COAs, we observed that the temperature region of both the α and β processes moved to higher temperature. Furthermore, with an increase in molecular size of bulky acyl group, the β region shifts were much larger than the α region, indicating that the mobility of the side chain became comparable to that of the main chain. Finally, when such a large bulky group, for example, benzoate was introduced, the micro‐Brownian motion of the side chain prior to that of the main chain ceased. The apparent activation energy for a third process (γ) due to the motion of the oligo‐oxymethylene parts in the side chain was estimated to
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