Ethylcellulose (EC), a widely used polymer for controlled drug release, consists of a cellulose backbone with hydroxyl groups substituted by ethyl groups. In these molecular dynamics simulations, we demonstrate that an increasing number of ethyl groups along the cellulose chains reduces the number of hydrogen bonds. Concurrently, a higher degree of substitution increases the glass transition temperature, corroborating experimental data. As anticipated, the simulations also reveal that chain mobility increases with a higher degree of substitution, with chain ends exhibiting greater mobility compared to the central segments of the chain.
Previous studies on another cellulose derivative used in controlled release, hydroxypropyl methylcellulose (HPMC), have experimentally shown that the position of the substituent along the chains significantly affects release and polymer properties. However, there are only a few experimental studies examining how the position of ethyl substituents within the repeating unit influences polymer properties such as density or glass transition temperature. This study indicates that the number of hydrogen bonds decreases most significantly when the hydroxyl group on carbon 6 is substituted, compared to the substitution of the hydroxyl groups at carbon 2 or 3. This results in lower density and a higher glass transition temperature. These findings suggest that molecular simulations can be a valuable tool for enhancing our understanding of the molecular interactions in cellulose derivatives.