Abstract: Aset of series of polyalchohols derived from neopentane[C(CH₃)₄] by means of the substitution of —CH₃ by other groups such as —CH₂OHand —NH₂ exhibit crystalline transformations which reversibly absorb large amounts of heat and can be used in thermal energy storage. The solid-solid phase transitions of pentylglycol(NPG), pentaglycerine(PG), pentarythritol(PE) and tris(hydroxymethyl)aminomethane(TAM) were studied by infrared spectroscopy at various temperatures and differential scanning analysis. Infrared spectra of four polyalchohols at room temperature show a strong absorption centered at 3300 cm^-1 which is identified as the —OHstretching band and indicate that between molecules there are hydrogen bonds which play a dominant role to the structure of low temperature phase(ordered phase). In the temperature range closely corresponding to the solid-solid phase transition —OHstretching band shifts to a higher wavenumber, which indicate that the hydrogen bands between molecules are broken. The out of plane deformation of the OHgroup which is rather sensitive to molecular interactions was also analyzed. Its frequency deviation to lower wavenumber with the increase of the temperature also indicate that the hydrogen bands are broken. The enthalpies and temperatures of solid solid phase transitions for polyalchohols measured by DSCmethod are consistent with the results of IRwhich can declare the mechanism of solid solid phase transition of polyalchohols. With the breaking of hydrogen bonds between molecules and the introduction of vibrational and rotational disorder polyalchohols exhibt crystalline transition. The structure of the high temperature phase which are known as orientationally disordered crystals(ODIC) or plastic phase are face centered cubic for NPG, PG, PEand body-centered cubic for TAM, which can be accounted for the difference between CH₂OHand NH₂ interactions.

Key words: Polyalchohols, Solid-solid phase transition, IR spectra at various temperatures, DSC method