Described herein are novel thermally reactive near-infrared absorbing acetal copolymers that undergo chemical and physical changes upon exposure to near-infrared radiation. Also described are the methods of preparation of the novel acetal copolymers starting either with vinyl-alcohol polymers or with acetal copolymers. Also described are the methods of use of the new near-infrared absorbing acetal copolymers in coatings used in lithographic offset printing plates that can be directly imaged with near-infrared laser imaging devices in computer-to-plate and digital offset printing technologies. The novel acetal copolymers are also useful in photoresist applications, rapid prototyping of printed circuit boards and chemical sensor development.