Determination of hydration stoichiometries and molar volumes of hydrated complexes in aqueous solutions of cellulosic ether polymers

Methods based on differential scanning calorimetry (DSC) and volumetric measurements were developed and used to determine the hydration stoichiometries and molar volumes of hydrated monomeric complexes of two polymers—methylcellulose (MC) and hydroxypropylmethyl cellulose (HPMC). When fully hydrated, the moles of bound water per mole of monomer were 5.9 and 10.7 for MC-A4M and HPMC-E4M, respectively. The molar volumes of the fully hydrated monomeric complexes were 486.9 and 580.0 mL/mole-monomer for MC-A4M and HPMC-E4M, respectively. The difference in bound water stoichiometries and molar volumes suggest a larger hydration layer consisting of bound water in HPMC than MC, which is consistent with its characteristic water affinity and gelation capabilities.