The physical characterization of extreme ultraviolet (EUV) ultra-thin underlayers (ULs) and their effects on photoresist EUV lithographic performance was investigated. UL polymer compositions were modeled to identify polymer compositions that would encompass a range of glass transition temperatures (Tg) and surface polarities. Eight UL polymers compositions were synthesized and characterized, demonstrating that polymer composition can dictate the surface polarity and Tg properties of cross-linked UL films. The Tg of UL films drops significantly for film thicknesses below ~30 nm. EUV imaging of open source and commercial resists on the eight UL films was evaluated. Resist adhesion improved when the surface polarity of the underlayers decreased. It was discovered that the coefficient of thermal expansion (CTE) plays an important role in determining the adhesion of resist to underlayers.