Abstract: A polyimide precursor monomer having an E value of 2.0 or more calculated by Equation 1 is selected among polyimide raw materials. A polyimide includes a structural unit derived from the polyimide precursor monomer having the E value of 2.0 or more. Optical properties of a polyimide film formed from the polyimide can be improved, and the optical properties of a polyimide film can be predicted from the E value of the polyimide precursor monomer even before production of the polyimide film.

Abstract: Disclosed is a saw blade capable of rapid cutting for various objects, such as jewelry, ferrite materials, stone, metallic materials, or ceramic tiles. The shape of the saw blade is modified such that performance and life time of the saw blade are improved. And also the manufacturing process for the saw blade is simplified, thereby reducing the manufacturing cost for the saw blade. The cutting tip is formed at upper and lower surfaces thereof with a mesh pattern, thereby enhancing the cutting performance by 30% as compared with that of a conventional cutting tip. The cutting tip represents superior cooling efficiency so that body of the saw blade is not broken during the cutting process, thereby ensuring safety of a worker and expanding the life time of the saw blade.