A highly soluble anthracene cyclic adduct with a thermally cleavable substituent was synthesized, and it was used as a donor unit in a series of donoracceptor type conjugated copolymers with improved processability. The removable group was eliminated under elevated temperature through retro DielsAlder reaction, which offered the corresponding copolymers with better planarity and rigidity. Thermogravimetric analysis (TGA), FT-IR, and UVvis spectroscopy were carried out to study the thermal cleavage process. Uniform films were easily formed from these precursor copolymers due to their good solution processabilty. Polymer solar cells were successfully fabricated through applying thermal annealing treatment on the blend films that were spin-coated from solutions of the precursor copolymers blended with fullerene derivatives. The best polymer solar cell device with a power conversion efficiency (PCE) of 2.15% was achieved based on copolymer PCOAEHDPP.