The miscibility of hydrogenated aromatic hydrocarbon resin (HR) with polybutadiene (PB) and polystyrene (PS) was investigated using turbidity measurement. Hereafter, the aromatic hydrocarbon resin having nine carbon atoms per monomer is referred to as C-9 resin. We found that C-9 resin, which has only a limited (or partial) miscibility with PB, became completely miscible with PB as the degree of hydrogenation (DH) in HR was increased to the optimum value of DH. The hydrogenation reaction of C-9 resin, which was conducted in the presence of a palladium (Pd) catalyst supported by activated carbon, converted aromatic rings in the resin to alicyclic rings. We controlled DH of C-9 resin by monitoring the amount of hydrogen used and the duration of reaction. The DH in HR was determined by elemental analysis and density measurement, and the chemical structures of HRs were determined by Fourier transform infrared spectroscopy, H-1 and C-13 nuclear magnetic resonance spectroscopy, and ultraviolet/visible Light spectroscopy. On the basis of the results of the upper critical solution temperatures of the blend systems investigated, it was found that a favorable interaction between PS and HRs decreased steadily with increasing DH and that there exists an optimum value of DH (approximately 0.7) in HR that gives the most favorable interaction with PB, The significance of the enhanced miscibility between PB and HRs, compared to the miscibility between PB and C-9 resin, was demonstrated by measuring the tack property of pressure-sensitive adhesives (PSAs), which were prepared from a polystyrene-block-polybutadiene-block-polystyrene (SBS triblock) copolymer and HRs, and from an SBS triblock copolymer and neat C-9 resin. We found that the probe tack of SBS triblock copolymer/HRs mixtures goes through a maximum (1100 g/cm(2)) for HR having DH = 0.7, at which HR has the most favorable interaction with PB as determined from turbidity measurement, whereas the probe tack of SBS triblock copolymer/C-9 resin mixture is negligibly small. These results were qualitatively interpreted by the solubility parameter approach using group contribution method. (C) 2000 Elsevier Science Ltd. All rights reserved.