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Abstract: Relationship between the chain conformation in the crystal lattice and the ultimate Young's modulus has been discussed on the basis of the crystal structural information revealed by the X-ray diffraction analysis for a series of arylate polyesters with long methylene segments (–[–COC6H4CO–O(CH2) m O–] n –). The X-ray structural analysis revealed that the molecular chains take the all-trans-zigzag conformations for all of the even-numbered polyesters and their model compounds as well as the odd-numbered polyesters with the methylene segmental length longer than (CH2)14. These chain conformations have been correlated well to the ultimate Young's modulus along the chain axis or the crystallite modulus E c , which has been estimated experimentally by the X-ray diffraction method under a constant stress and also predicted theoretically using the X-ray-analyzed crystal structures on the basis of the molecular mechanics method. The E c was found to show the minimum at around m = 4–6 and increased gradually with an increment of m and approached the crystallite modulus of polyethylene, 235 GPa (X-ray value) ∼ 316 GPa (calculate) at an infinite m value. This behavior of E c as a function of the number of methylene segmental units m was reasonably interpreted by developing the theoretical equation of E c for a simplified zigzag chain model composed of a repetition of two linear rods representing the benzene–ester and methylene segmental parts respectively. These findings may promise that the mechanical property of arylate polyester can be controlled by adjusting the methylene segmental length m. [Copyright &y& Elsevier]

Crystal structures have been determined by the X-ray diffraction analyses for a series of aromatic polyesters –[–O(CH2) m O–COC6H4CO–] n – (mGT) with the long methylene sequence (m = 9–20) and their model compounds. The X-ray diffraction spots of these polyesters were observed more or less to shift upward and downward slightly from the averaged horizontal layer lines, indicating the tilting phenomenon of the molecular chains from the draw direction, the analysis of which was helpful for the definite determination of the unit cell parameters. For example, the c axis of 10 GT was found to be tilted by about 1° from the drawn axis in the 10 tilt plane. The unit cell parameters obtained by the quantitative analysis of the tilting phenomenon were a = 4.77 ± 0.01 Å, b = 5.66 ± 0.01 Å, c (f.a.) = 20.7 ± 0.1 Å, α = 108.2 ± 0.1°, β = 122.7 ± 0.2°, and γ = 97.1 ± 0.1°. In the case of 20 GT, the tilting phenomenon was not observed in the X-ray fiber diagram. The triclinic unit cell parameters were determined for 20 GT: a = 4.59 ± 0.02 Å, b = 5.75 ± 0.02 Å, c (f.a.) = 33.3 ± 0.1 Å, α = 113.2 ± 0.2°, β = 116.6 ± 0.2°, and γ = 98.1 ± 0.2°. The space group was P for both of 10 GT and 20 GT. One chain is included in the unit cell. The chain conformation is of the all-trans-zigzag type. The reliability factor or the measure of the agreement between the observed and calculated X-ray diffraction intensity was 18.8% for 10 GT (90 reflections in total) and 18.5% for 20 GT (67 reflections). The crystal structures of 12 GT and 16 GT were found to be essentially the same as those of 10 GT and 20 GT. As for the odd-numbered mGT or 9 GT, 11 GT and 15 GT, the most plausible structure models were built up, which gave the good correspondence to the observed diffraction patterns semi-quantitatively. As the total number of methylene monomeric units was increased, the chain conformation was found to change from the trans-gauche combined form (3 GT and 5 GT) to the all-trans form (15 GT). The single crystal structure analysis of the low-molecular-weight model compounds confirmed the reasonableness of the crystal structures of the corresponding polymers. [ABSTRACT FROM AUTHOR]