The Relations Between Structure And Property For Polyamides Based On Quantum Chemical Methods

The structural units of polyamides had been optimized and their quantum chemical descriptors had been obtained by quantum chemical calculations. The quantitative structure property relationships (QSPRs) between the quantum chemical descriptors and properties of these polymers had been established by multiple linear regressions (MLR), factor analysis (FA) and error back propagation artificial neural network (BP-ANN) methods. The factors affected on the polymers properties had been analyzed and in the paper. In the same time, these ¹³C-NMR chemical shifts (δiso) and the vibrational force fields of three kinds of oligomers were calculated, the polymers ¹³C-NMR chemical shifts were studied by group contribution method, and assignment of the vibrational fundamentals was also performed according to experimental results.Firstly, the QSPRs between quantum chemical descriptors and Tg, n andρ298K for polyamides had been developed using MLR and BP-ANN methods. The calculated results indicated that the most import factors affected on glass transition temperature Tg are the proportion of methylene to acylamino in the backbone chain PMA, the energy of the lowest unoccupied molecular orbital ELUMO, atomic charge for oxygen in acylamino Q_O-, the relative molecular weight of the repeating unit M and the internal energy U. the most import factors affected on density at room temperatureρ298K are the energy of the highest occupied molecular orbital EHOME, Q_O- and Et, the most import factors affected on index of refraction n are PMA, EHOMO, ELUMO and molecular dipole momentμ. The results of QSPRs indicated that the calculated values are in good agreement with experimental ones.Secondly, these QSPRs between quantum chemical descriptors and Melting Point T_m for polyamides had been developed using MLR, FA and BP-ANN methods. The calculated results indicted that the most significant descriptors affected on T_m are the value of benzene rings in the backbone chain LB, PMA, total molecular energy Et and Q_O-. These calculated results agree with the experimental values well. The calculated results obtained by BP-ANN method have met the experimental data better than ones obtained by MLR.Thirdly, these ¹³C-NMR chemical shifts (δiso) were studied by RHF-GIAO method and 6-311+G (d, p) basis set. Theseδiso were calculated with respect to theoreticalσiso of the TMS (tetramethylsilane). In order to test the calculated results, group contribution method is used to estimateδiso of all oligomers. Oligomeric approach had been employed to calculateδiso of the corresponding polymers. The calculatedδiso were...