The second virial coefficients A(2) of ring polystyrenes with high purity in cyclohexane were measured by light scattering in the temperature range 27.0-34.5 degrees C. The purity of four samples with M-w of 16k, 42k, 110k and 570k was determined to be all over 96% by HPLC. It has been found that A(2)s of all the samples are definitely positive at the theta temperature of linear polystyrene, 34.5 degrees C, and the measured values for four samples converged to zero at 27.7 degrees C with decreasing temperature. This value is below the previously reported one, but it is quite consistent with the predicted value based on the topological repulsive interaction among the ring polymer molecules. (c) 2009 Elsevier Ltd. All rights reserved