Monte Carlo simulations for model polymer chains composed of hard spheres w
ith square-well attractions were performed to find a precise relation betwe
en the parameters of a crossover theory and the parameters of the square-we
ll chain. For sufficiently large bond lengths, there was a direct relation
between the effective parameters of the crossover theory and the second- an
d third-virial coefficients of the square-well atoms. For the systems under
study, the theta temperature is close to the Boyle temperature of the disc
onnected monomers, is mainly dependent on the details of the monomer-monome
r interactions, and is only weakly dependent on the bond length of the chai
n. Above the theta temperature, the crossover theory is in good agreement w
ith the simulation data. Near the theta point, the main effect of tricritic
al corrections is a shift in the critical amplitudes. Other effects are ext
remely small. The simulation data are consistent with the tricritical cross
over theory. However, more precise data are needed to quantitatively test t
he tricritical crossover theory. (C) 1999 American Institute of Physics. [S
0021-9606(99)50536-9].