Silica modified with N-2-aminoethyl-3-aminopropyttrimetho-xysilane (1) or octyltriethoxysilane (11) was used to fill, 5, 10 or 20%, a polybutadiene-urethane oligomer (M = 4000). This was examd. by inverse gas chromatog. to det. Floty-Huggins x(12)(infinity)-parameters in 10 binary systems with solvent-type test compds. Zhao-Choi (Polymer, 42 1075 (2001)) method was also tried to det x(23) independent of the test compd. Results were consistent. The modified SiO2-filled composites interacted strongly (with CHCl3 and Et2O, lowest x(12)(infinity)). More II made interactions weaker (except for dichloroethane). I-modified SiO2 was effective at 5%. The x(23) (measure of oligomer-filler interactions) showed modified SiO2 to be most effective at 5 and 10% (363, 393 K).