MODELING OF THETA-CONDITIONS FOR BISPHENOL-A POLYCARBONATE SINGLE CHAINS

Assessing conformational dimensions of macromolecules is atopic of lon g-standing interest. Because of its simplicity, it is attractive to in vestigate the chain properties in Theta-conditions. Under these specia l conditions, the effects of excluded volume of the segments of the po lymer chain vanish. The molecular chain is only subject to local const raints resulting from the bond structure and the hindrance to rotation s about bonds. To model Theta-conditions a contour length dependent cu toff is introduced ensuring that only nonbonded interactions oi atoms of neighbouring monomeric units are taken into account for energy calc ulations. Using this energy model we will show that it is possible to model Theta-conditions of a single bisphenol-A polycarbonate (BPA-PC) chain in vacuum by two different methods: (i) (Pseudo-) Langevin dynam ics simulations and (ii) regular reassignment of randomly generated at om velocities during a molecular dynamics simulation. Both methods can be used to avoid oscillative dynamic behaviour of the chain. Calculat ions of the end-to-end vector and the radius of gyration of the equili brium ensembles derived from simulations at different temperatures sho w good agreement with experimental data. Thus our model techniques are well suited to simulate Theta-conditions with small computational exp ense.