Modelling of Θ-conditions for bisphenol: A polycarbonate single chains

Assessing conformational dimensions of macromolecules is a topic of long-standing interest. Because of its simplicity, it is attractive to investigate the chain properties in Θ-conditions. Under these special conditions, the effects of excluded volume of the segments of the polymer chain vanish. The molecular chain is only subject to local constraints resulting from the bond structure and the hindrance to rotations about bonds. To model Θ-conditions a contour length dependent cutoff is introduced ensuring that only nonbonded interactions of atoms of neighbouring monomeric units are taken into account for energy calculations. Using this energy model we will show that it is possible to model Θ-conditions of a single bisphenol-A polycarbonate (BPA-PC) chain in vacuum by two different methods: (i) (Pseudo-) Langevin dynamics simulations and (ii) regular reassignment of randomly generated atom velocities during a molecular dynamics simulation. Both methods can be used to avoid oscillative dynamic behaviour of the chain. Calculations of the end-to-end vector and the radius of gyration of the equilibrium ensembles derived from simulations at different temperatures show good agreement with experimental data. Thus our model techniques are well suited to simulate Θ-conditions with small computational expense.