Morphology and Temperature Phase Transitions in α,ω-Alkanediols with Different Chain Lengths

摘要

A comparative analysis of phase transitions in diols with various chain lengths [(CH_2)_(44)(OH)_2 and (CH_2)_(22)(OH)_2] and changes in their absorption spectra with temperature have been investigated by DSC and FTIR. Analysis of the DSC data has led to the conclusion that the low-temperature phase transition of (CH_2)_(22)(OH)_2 in a solid state (T_(s-s) = 367.1 K) is a phase transition of the first order, while the high-temperature phase transition (T_m = 376.3 K) is of the second order, i.e., a transition of the order-disorder type. Splitting of the IR absorption bands into doublets at 720-730 cm~(-1) and 1463-1473 cm~(-1) indicates that crystalline subcells in the lamellae of both diols are orthorhombic lattices with the parameters typical of hydrocarbons. IR spectra showed that at the phase transition temperature T_(s-s) transformation of an orthorhombic subcell into a hexagonal one occurs. This type of molecular chain packing remains the same up to the melting temperature T_m. In a (CH_2)_(44)(OH)_2 diol, the ortho-hexagonal subcell transition occurs only at the melting temperature (390.0 K). The wide IR band in the region from 3000 cm~(-1) to 3600 cm~(-1) shows that end hydroxyl groups of diol molecules form, on the surfaces of lamellar crystals, long (polymer) regular sequences consisting of intermolecular hydrogen bonds.