Monomers and polymers useful for forming photoresists are provided. More particularly, photoresists, as well as monomers and polymers for photoresists useful in micro-lithography, specifically monomers bearing acid-labile groups of reduced optical density. The resulting photoresists exhibit improved transparency to 157 nm light. The photoresist compositions are composed of a mixture of at least one water insoluble, acid decomposable polymer which is prepared from at least one monomeric unit which comprises an acid labile group of the formula —OC(CH3)2CF3 and which is substantially transparent to ultraviolet radiation at a wavelength of about 157 nm and at least one photoacid generator capable of generating an acid upon exposure to sufficient activating energy at a wavelength of about 157 nm.