Theoretical analysis of conformational energies,unperturbed dimensions,and dipole moments of poly(dichlorophosphazene) |
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Authors: | Enrique Saiz |
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Abstract: | A theoretical analysis of the conformational energies of poly(dichlorophosphazene) (PDCP) is presented. The results indicate that the bond pair P? N? P possesses a considerable conformational freedom, whereas the bond pair N? P? N is relatively rigid. This difference explains the low glass transition temperatures Tg and large end-to-end distances measured for polyphosphazenes. A statistical model containing four rotational isomers (ie., trans, gauche, cis, and negative gauche) is developed and used to calculate unperturbed dimensions and dipole moments of PDCP. The results, obtained at 25°C with n = 400 skeletal bonds (200 repeating units), were Cn = 〈r2〉0/nl2 = 13.5; CT = 103d(ln〈r2〉0)/dT = ?3.0 K?1; Dn = 〈μ2〉/nμ = 0.35; DT = 103d(ln〈μ2〉)/dT = ?3.4 K?1. All the calculated magnitudes are extremely sensitive to the energy Eσ that controls the statistical weights of the conformations tg, tc, tg?, gt, ct, and g?t relative to tt for the bond pair P? N? P. A qualitative explanation for this sensitivity is discussed. |
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