  My means of extensive Monte Carlo simulations the mean radius of gyration and
the end-to-end distance are calculated for a single chain in a solvent over a
broad range of volume fractions, pressures and temperatures. Our results
indicate that in general, the chain collapses as temperature increases at
constant pressure, or as density decreases at constant temperature. A minimum
in the radius of gyration and the end-to-end distance occurs near the Lower
Critical Solution Temperature (LCST) and slightly above the coil-to-globule
transition temperature, where the chain adopts a quasi-ideal conformation,
defined by the balance of binary attractive and repulsive interactions. At
temperatures well above the LCST, the chain expands again suggesting an Upper
Critical Solution Temperature (UCST) phase boundary above the LCST, forming a
closed immiscibility loop. However, this observation strongly depends on the
solvent-to-monomer size ratio.
