Monte Carlo simulation of the θ‐conditions of poly(methylene): Temperature dependence of the long‐range screening factor

Structures of methylene groups were modelled using the united atom approximation, i.e. each group was considered as an individual center for van der Waals interactions. In these simulations the environment of the macromolecules in liquid or amorphous states was taken into account by the introduction of a screening factor β for the attractive part of the methylene‐methylene interaction that was modelled by a Lennard‐Jones potential (U(r) = A/r12 − β B/r6). The value of βθ that corresponds to θ‐conditions was established for several temperatures between 200 K and 1 500 K from the dependence of the end‐to‐end distance and the radius of gyration of the individual structures on the number of monomeric units in the chain. The dependence of the θ‐conditions on the thermodynamic stiffness was investigated. The results for the nonself‐intersecting chain were compared with self‐intersecting chains, where standard (β = 1) and modified Lennard‐Jones potentials were taken into account for a specified number of nearest neighbours only. The mean square radii of gyration and end‐to‐end distances are nearly identical for chains under θ‐conditions and for a self‐intersecting chain simulated using the standard Lennard‐Jones potential for the 1,5‐interactions at all temperatures.