Crosslinking statistics, 3. Relation between relative reactivity and accessibility of cellulose hydroxyl groups

Abstract

AbstractFrom the results of a structural analysis of cellulose crosslinked by a bifunctional reagent conclusions can be drawn merely on the distribution of crosslinks among individual hydroxyl groups. No information is available to what extent this distribution is caused either by different relative reactivities of the hydroxyl groups or incomplete accessibility of glucose units. If each glucose unit had the same chance of reaction, at low levels of conversion only monosubstituted units should be present in the reaction product. If, however, some higher substituted units are present, this means that at a certain level of conversion there must have been a smaller number of units capable of reaction to which relatively more reagent had access. The relation between relative reactivity and accessibility of cellulose hydroxyl groups obeys certain statistical laws of random selection. A theory explaining these laws is developed in the present work and supported by good agreement with experimental results exemplified by microcrystalline cellulose crosslinked by epichlorohydrin (1‐chloro‐2,3‐epoxypropane). The relative reactivities of cellulose hydroxyls were found to increase in the order OH‐3, OH‐6, OH‐2 in the crosslinking reaction with epichlorohydrin.