Phase Transitions of Pure Long-Chain <i>α</i>,<i>ω</i>-Alkanediols from C13 to C24

Abstract

Abstract A series of pure α,ω-alkanediols HO-(CH2)n-OH (n = 13—24) was prepared and the effects of chain length and parity on their thermal properties were investigated. Crystal structures of odd α,ω-alkanediols were orthorhombic, while those of even α,ω-alkanediols were monoclinic. α,ω-Alkanediols with n = 13—24 showed solid–solid transitions except for n = 14. The solid–solid transition was found to be reversible. Transition temperatures from the crystal to the high-temperature phase indicated distinctive and regular odd-even effects, while from the high-temperature phase to the liquid, slightly odd–even effects were noted. The average enthalpy increment per methylene unit from the crystal to liquid for odd α,ω-alkanediols was 4.0 kJ mol−1. Enthalpies of transition from crystal to high-temperature phases considerably exceeded those of n-alkanes. HOC13H26OH lost 62% total enthalpy at the solid–solid transition and only 38% at melting. High-temperature phases of α,ω-alkanediols may possibly be liquid crystal phases.