이후 반응액의 온도를 상온으로 내리고 글루타르산 무수물 12.5부를 투입하고 80℃에서 6시간 반응하였다.
Thereafter, the temperature of the reaction solution was lowered to room temperature, 12.5 parts of glutaric anhydride was added and reacted at 80°C for 6 hours.