MONTE-CARLO SIMULATION OF THE THETA-CONDITIONS OF POLY(METHYLENE) - TEMPERATURE-DEPENDENCE OF THE LONG-RANGE SCREENING FACTOR

Structures of methylene groups were modelled using the united atom app roximation, i. e. each group was considered as an individual center fo r van der Waals interactions. In these simulations the environment of the macromolecules in liquid or amorphous states was taken into accoun t by the introduction of a screening factor p for the attractive part of the methylene-methylene interaction that was modelled by a Lennard- Jones potential (U(r) = A/r(12) - beta B/r(6)). The value of beta thet a that corresponds to theta-conditions was established for several tem peratures between 200 K and 1500 K from the dependence of the end-to-e nd distance and the radius of gyration of the individual structures on the number of monomeric units in the chain. The dependence of the the ta-conditions on the thermodynamic stiffness was investigated. The res ults for the nonself-intersecting chain were compared with self-inters ecting chains, where standard (beta = 1) and modified Lennard-Jones po tentials were taken into account for a specified number of nearest nei ghbours only. The mean square radii of gyration and end-to-end distanc es are nearly identical for chains under theta-conditions and for a se lf-intersecting chain simulated using the standard Lennard-Jones poten tial for the 1,5-interactions at all temperatures.