Prediction of polymer crystal structures and properties: polyethylene and poly(oxymethylene)

• Published in: Macromolecules 1988-01, Vol.21 (1), p.200-208
• Main Authors: Sorensen, R. A, Liau, W. B, Kesner, L, Boyd, R. H
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma00179a039

Applying a method previously developed, molecular mechanics is used to calculate in a unified manner, from transferable conformational energy functions, the packing parameters and energy, vibrational dispersion curves, heat capacity, and thermodynamic functions, elastic constants, and refractive indices of polyethylene (PE) and poly(oxymethylene) (POM). PE was chosen as a "standard" to illustrate the method and POM because it occurs in two crystal forms occasioned by the effect of packing forces in distorting the intramolecular torsion angles and because its crystal properties are of interest. Compared to the free--GG--helix, the helix in the orthorhombic form is under compression and that in the hexagonal form under tension. Good agreement between calculated and experimental structures was found. The packing energy of the orthorhombic form is slightly more favorable (1.5 kJ/mol) but the free energies at room temperature are more comparable (0.7 kJ/mol). The calculated heat capacity of POM over the range 100-300K is in reasonable agreement with the extrapolated experimental values of Gaur and Wunderlich and significantly higher than those of Illers. The C sub 33 elastic constant of PE is calculated to be 341 GPa and that of (hexagonal) POM is 83 GPa. 41 ref.--AA