Effect of Substituent Groups on Hydrogen Bonding of Polyhydroxystyrene Derivatives

Abstract

Poly(2-hydroxystyrene) (PoHS), poly(3-hydroxystyrene) (PmHS), poly(4-hy-droxystyrene) (PpHS), and their acetylated polymers were prepared. Attention was directed to the effect of substituent groups and sorbed water on the molecular motion of the polyhydroxystyrene derivatives. The glass transition temperature (Tg) of these polymers and the phase transition of water sorbed on the polymers were studied by differential scanning calorimetry (DSC). Bound water content was calculated from total amounts of sorbed water and crystallization enthalpy of water. The Tg of each polymer increases linearly with increasing mole fraction of hydroxystyrene (HS). It was clarified that the Tg increase is dependent on the replacement of acetoxyl groups with hydroxyl groups, since formation of hydrogen bonding occurs through the hydroxyl groups of the polymers. It was also found that the hydroxyl group of PmHS located at the 3-position of each aromatic ring formed hydrogen bonds the most readily, while that located at the 4-position did so second to this. The OH group of PoHS located at the 2-position formed hydrogen bonds with difficulty. Two exothermic peaks for the crystallization of water sorbed on each of the above polymers were observed on a DSC curve: one was a sharp peak (Peak I) of free water observed at about 255 K, and the other, a broad small peak (Peak II) of freezing bound water observed at about 230 K. Judging from the amounts of water calculated from the crystallization enthalpy of water sorbed on each polymer, there seems to be non-freezing water which does not crystallize. The bound water content of each polymer increased with increasing mole fraction of HS. The increase in bound water content of PmHS was highest with increasing mole fraction of HS.