Chemical contrast at subwavelength spatial resolution (lambda /10) is achieved using a fiber-based, infrared near-field microscope, at 3 mum wavelength. Chemically amplified polymer photoresists (poly(t-butylmethacrylate)), patterned by ultraviolet radiation and 250 nm thick, are imaged using infrared (TR) wavelengths situated around the OH stretch band of the polymer, a region sensitive to photochemical changes associated with latent image formation. The key technical points that enable near-field infrared absorption measurements down to 0.05% absorption sensitivity are discussed together with the major contrast mechanisms involved in image formation. The measurements are complemented by confirming studies using confocal infrared microscopy and depth profiling. The exposure dose dependence of the acid catalyzed chemistry, after the postexposure bake step, was studied on line/space patterned samples. The OH subgroup absorption maps of the patterned polymer film exhibit features that are not present in the topographical changes (shrinkage) induced by the postexposure polymer chemistry and illustrate significant potential of the IR near-field microscopy as an analytical tool for polymer chemical physics.