A facile method to tune the phase transition temperature of thermosensitive polymers is to introduce an additive; however, the influence of additives is usually limited. Here the influence of poly(vinyl alcohol) (PVA), a polymeric additive, on thermal behavior of copolymers of acrylamide (AAm), N,N-dimethylacrylamide (DMAA), and 3-(acrylamido)phenylboronic acid (3-AAPBA), P(AAm-DMAA-3-AAPBA), was studied. With increasing AAm content, the phase transition temperature of the copolymers increases gradually. They finally become nonthermosensitive when AAm content exceeds 20 mol %. To study the influence of PVA on the copolymers, they were incorporated into thin films via layer-by-layer (LBL) assembly, using phenylboronate ester bonds between them as a driving force. Because the two polymers in the films were drawn very close to each other, the ability of PVA to depress phase transition temperature of copolymer is significantly amplified. As a result, an unprecedented large depression on phase transition temperature was observed. As an example, the phase transition temperature of P(AAm-DMAA-3-AAPBA)(15) is significantly decreased from 86 degrees C in solution to 14 degrees C in the LBL film, corresponding to a 72 degrees C decrease. More importantly, some copolymers that do not exhibit thermosensitive behaviors in solution can be turned to be thermosensitive, as their phase transition temperature can be decreased from >= 100 to <100 degrees C due to the extraordinarily large ability of PVA to depress the phase transition temperature. Consequently, films from these nonthermosensitive copolymers also present a heat-induced phase transition.