Computer simulation of the heat-resistant polyimides ULTEM™ and EXTEM™ with the use of GROMOS53a6 and AMBER99 force fields

Abstract

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Influence of the carbon nanotube surface modification on the microstructure of thermoplastic binders

“…52,59,60,64 The simulation was performed in the NpT ensemble at a temperature of 600 K under a pressure of 1 bar. 52,59,60,64 The simulation was performed in the NpT ensemble at a temperature of 600 K under a pressure of 1 bar.…”

“…Test simulations showed that the use of the Nose-Hoover thermostat and the Parhinello-Rahman barostat do not lead to any significant changes in the discussed structural properties. 52,64 Ewald summation method (PME) 76 was used to account for the electrostatic interactions. 74 The values of the partial charges for the atoms of carboxyl groups attached to the CNT were taken as standard values for the Gromos53a5 force field 72 which was parameterized for simulating systems in the media with low permittivity.…”

“…To maintain the set lengths of the bonds between the atoms, the LINCS algorithm was used. 52,53,[60][61][62][63][64][65] The equilibration procedure included stages of the system compression from the initial low-density configuration (polymer gas), cyclic annealing within the temperature range of 600 to 290 K, equilibration at a high temperature for 1.5 μs, and further production run during 1 μs. Parametrization of the charges in this force field was done using the HF/6-31G* method.…”

“…58,[63][64][65] The increased flexibility of the chain, and enhanced dipole-dipole interactions in the PI R-BAPS, as opposed to the R-BAPB, prevent crystallization of this polymer even in the presence of carbon nanoparticles which can act as good nucleants. Notably, the loading of modified CNTs with polarized carboxyl groups on the surface into the R-BAPS may have a different influence on the polymer structure, compared to that of the R-BAPB polyimide where electrostatic interactions do not play such a significant role as in the case of the R-BAPS.…”

Achievements in polycondensation and condensation polymers

“…This effect is explained by the formation of associates via electrostatic interactions between sulfur and oxygen atoms of the sulfone group [61]. Computer simulation experiments revealed that these interactions play an important role in the absence of such groups as well [69]. The transport characteristics of PIs were found to be affected by the presence of rigid or flexible frag ments.…”