Several concepts concerned with molecular weight regulator were introduced

including chain-transfer agent

molecular weight stabilizer

viscosity stabilizer and end capping agent. Their connections

similarities and differences with molecular weight regulator and applications were summarized detailly in the addition polymerization and condensation polymerization. In the addition polymerization

the molecular weight regulator and chain-transfer agent are the same concept. Whileas in the condensation polymerization

there are several concepts concerned with with molecular weight regulator. There is no uniform definition. It was always called viscosity stabilizer because the relationship between the molecular weight and viscosity is very intimate. And it was pointed out that synthetically using the knowledge of polymer physics and polymer chemistry was very important when teaching the polymer physics or polymer chemistry.