In the textbook of polymer chemistry, it is well known that due to the steric hindrance effects in combination with stability of the tertiary benzylic α-methylstyryl radical, there exists a dynamic equilibrium between monomer α-methylstyrene (AMS) and its polymer (PAMS) when the temperature is greater than 61 ℃ (the ceiling polymerization temperature).While another fact is that when AMS was copolymerized with other monomer like styrene, the copolymer obtained not only showed better mechanical property and higher Tg but also very good thermo/radiation stability.A deep thinking for these phenomena results in a basic understanding behind them: for the homopolymer or copolymer of AMS, when temperature is over the ceiling value, there possibly is a dynamic equilibrium between fragmentation and coupling of polymeric chains by a radical mechanism too.