You might want to use an inhibitor like hydroquinone if you are heating up your reaction mixture.

If your reaction generate free radical, cation or anion, so all these species cause the initiation of polymerisation reaction. Now if you want to stop that you need to either avoid using any substance generate what I mention above or use inhibitors.

Esmat Jalalvandi ！ thank you ~

Ali Alsuraifi thank you~