Heat resistance index is the glass transition temperature, to meet the high temperature, the basic point is to have a high glass transition temperature. Requirements for engineering plastics can be injection molded, TG should be at 250 ℃, another high TG, will enable the processing temperature exceeds 400 ℃. This is regardless of the polymer and the processing equipment is unacceptable. Because organic polymer material begins to decompose or be cross-linked at 400 ℃ and down. Even a very low speed, it is difficult to maintain a constant production without affecting the quality of the product. In addition, in more than 400 ℃ long-term work also makes molding equipment is difficult to maintain precision.