In this work, poly(N-isopropylacrylamide) (PNIPAAm) was incorporated into previously oxidized PS and PET surfaces by grafting using two photo-initiation pathways. The incorporation of PNIPAAm was observed by drop water contact angle measurements, dyeing with Methylene Blue and AFM images analysis of the virgin and modified polymers. It was verified that the grafting process depends on the chemical surface environment. The grafted surfaces are hydrophilic below 32 degrees C and hydrophobic above this temperature. The transition is due to the incorporated PNIPAAm. This characteristic gives to the grafted materials potential to be applied as biomaterials.