The crystal stucture determination of low and high temperature phases of Tris (Ethylene Terephthalate)

Abstract

Tris (Ethylene Terephthalate) is an oligomer of Polyethylene Terephthalate with a chemical formula of -[O.00.C 6H 4 .CO.O.CH2 .CHJ 3 -. It has two phases, namely the Low Temperature phase (Type A) which isstable below 801C; and the High Temperature Phase (Type B) - stable between 800C and its melting temperature 320 0C. The crystal structures of these two phases have been determined by X-ray diffraction of single crystals. The LTP crystals were crystallised from its solution in DMF at room temperature.
The LTP crstals were found to have a monoclinic unit cell and spac%C; the unit cell is a = 16.98A°, b = 19.59A °, c = 8.43A and $ 96.240 with z = 4 molecules/unit cell; d(obs) = 1.367 g/cm 3 . The HTP trimer crystals were formed from a hot solution of tris(ethylene terephthalate) and Dekalin above 1200C. These crystals were found to have a density of 1.321 g/cm 3 and a hexagonal unit cell of a = b = 15.37A ° , c = 20.78A° and y = 1200 ; Z = 6 molecules/ unit cell; Space Group of
The two structures were refined to R-Factors of 9.66% and 14.86% respectively. The molecular conformations of both
phases are the same; their ester-groups in ICISt conformation and the glycol residue links in 'gauchC' formation. The trimer molecules in the LT phase are arranged in an ordered manner; whilst in the HTP trimer the glycol residue links are disordered, with two possible conformations for each link.