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

Vyas, Ramesh Harakhji (1984) The crystal stucture determination of low and high temperature phases of Tris (Ethylene Terephthalate). Doctoral thesis, University of Central Lancashire.

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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.

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