Unit cell dimensions of poly(ethylene terephthalate)

Abstract

Abstract The density of crystals of poly(ethylene terephthalate), (PETP), Q c is checked by X‐ray diffraction assuming a triclinic unit cell and the indices of reflections as found by Bunn. The following unit cell dimensions are found: a = 4,48Å, b = 5,85Å, c = 10,75 Å, α = 99,5°, β = 118,4°, and γ = 111,2°. This gives the density Q c as 1,515g/cm 3 which is about 4% higher than that reported by Bunn. Negligible differences in spacings for samples annealed at different temperatures (120°C–260°C) have been found. Only for an annealing temperature of 100°C the higher d ‐values lead to Q c = 1,484g/cm 3 . For undrawn PETP films annealed at 250°C the same value of Q c as for drawn PETP was obtained on the basis of Guinier X‐ray patterns. No systematic variation of crystal plane spacings was found for drawn PETP fibers annealed at 220°C and containing mole fractions of 1,7 to 4,2% diethylene glycol, (2,2′‐oxydiethanol), as comonomer.