Sum-frequency vibrational spectroscopy was used to study how linearly polarized UV irradiation could cause bond breaking and alter the surface structure of a polyimide. The spectroscopic results allowed the determination of an approximate orientational distribution of the polymer backbones at a rubbed surface. They also permitted deduction of rates of bond breaking of the backbones at the surface by UV dosage. The surface anisotropy resulting from bond breaking by linearly polarized UV irradiation was found to be relatively small,. suggesting a weak azimuthal anchoring energy for liquid crystal films deposited on such a surface.