The effects of macromolecular architecture on the osmotic pressure pi and virial coefficients (B-2 and B-3) of star and comb polymers in good solvents are studied by dissipative particle dynamics simulations for both dilute and semiconcentrated regimes. The dependence of the osmotic pressure on polymer concentration is directly calculated by considering two reservoirs separated by a semipermeable, fictitious membrane. Our simulation results show that the ratios A(n+1) equivalent to Bn+ 1/(R) over cap (3n)(g) are essentially constant and A(2) and A(3) are arm number (f) dependent, where (R) over cap (g) is zero-density radius of gyration. The value of dimensionless virial ratio g=A(3)/A(2)(2) increases with arm number of stars whereas it is essentially arm number independent for comb polymers. In semiconcentrated regime the scaling relation between osmotic pressure and volume fraction, pi(proportional to)phi(lambda), still holds for both star and comb polymers. For comb polymers, the exponent lambda is close to lambda* (approximate to 2.73 for linear chains) and is independent of the arm number. However, for star polymers, the exponent lambda deviates from lambda* and actually grows with increasing the arm number. This may be attributed to the significant ternary interactions near the star core in the many-arm systems. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3099721]
