Effect of OH group on the water vapor sorption property of adamantane-containing polymer membranes

The synthesis and characteristics of adamantane-containing acryl or methacryl polymers were investigated, focusing on the effects of the hydrophobic adamantyl unit and the hydrophilic OH group. The water vapor sorption property of adamantane polymer membranes was determined at 35 °C. The membrane density which represents the packing of polymer segments increased with increasing the OH groups and the polymer cohesive energy density (CED), which reflects the polarity of polymers. The water vapor solubility in OH-containing adamantane polymer membranes was higher than that in non-OH-containing adamantanes due to the high interaction between the OH group and the water molecules. Therefore, the OH groups in the adamantane unit give the sorption site of the water molecules in the membranes. In addition, we found that the stronger interaction by OH groups between the water molecules and polymers can prevent the clustering of water molecules based on the Zimm–Lundberg analysis.