POLYURETHANE ELASTOMERS BASED ON AROMATIC DIISOCYANATES FOR PASSIVE ISOLATION SYSTEMS Polyurethanes (PUs) based on polyester polyol and aromatic diisocyanate are used as passive isolation bearings in buildings applications. In the present study polyesterdiol and 4,4-diphenylmethane diisocyanate (MDI) have been used in polyurethanes, using glycerine, ethylene or diethylene glycols as chain extenders. Effect of varying the concentrations of diisocyanates and structure of chain extenders on PUs have been discussed with reference to mechanical properties. IR and thermal analysis techniques (TGA and DSC) were used for characterization. The results expose that aromatic character of diisocyanates raises the temperature required to achieve the flexibility in the polymer. Based on their mechanical properties, PUs has great potential for applications where excellent wind and earthquake loads resistance, dynamic-to-static stiffness ratio and vertical and lateral load characteristics are required.