Phase Transitions of Pure Long-Chain α,ω-Alkanediols from C13 to C24

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.

Macromolecular Crystal Engineering Based on Segmented Polymers: Influence of Heteroatoms on the Thermal Properties and Crystallization of m,n‐Polyurethanes Derived from Long‐Chain, Heteroatom‐Containing, Monodisperse α,ω‐Diols

“…These heteroatom-containing diols had much lower melting points and enthalpy values than the corresponding purely aliphatic diols. [6,9,24] It has been suggested that ether links activate the rotation of neighboring methylene groups, resulting in an increase in flexibility, which could cause a lowering of the melting temperature. [28] Additionally, unlike the corresponding aliphatic diols, the heteroatom-containing diols did not exhibit a solid-solid rotator phase transition upon heating.…”

“…* and * represent data from this paper and literature (see refs. [6,9,24] ), respectively. Scheme 2.…”

“…than 22 consecutive methylene groups), several steps are typically required, with overall yields that are rather low. [9][10][11][12][13][14][15][16] Longchain, purely aliphatic diols can often be extracted and isolated from natural products. [17][18][19][20][21][22][23] Unfortunately, the purity of these diols is often low, and removal of the contaminants, typically other a,o-diols or a,o-diacids, is extremely difficult.…”

1,17-Heptadecanediol

“…In these structures, the molecules form a layer structure which is similar to that found in smectic A liquid crystals. In addition, phase transitions in ,3-alkanediols with C 13 ±C 24 were studied and a linear relation between the longest unit-cell length and number of C atoms was reported using powder X-ray diffraction (Ogawa & Nakamura, 1999). Fig.…”

Энергоемкость PCM-материалов На Основе Н-Алканов

“…При охлаждении из расплава наблюдается обратная картина: образец выделяет тепло (экзотермический процесс), при T min 2 происходит его кристаллизация, а при T min 1 -твердофазный переход [2,4].…”