| Name | Molecular weight regulator |
| Synonyms | Molecular weight regulator |
| Use | Use for molecular weight regulation in the polymerization of monomers |
overview
One of the characteristics of the addition polymerization reaction, especially the free radical polymerization reaction, is that it is prone to chain transfer reaction. The chain transfer reaction can cause the branching of polymers. For example, the free radical polymerization reaction of polyethylene causes molecular branching due to chain transfer, and the crystallinity is reduced. If the molecules are not arranged tightly, low-density polyethylene is obtained, and the coordination polymerization has no chain transfer reaction. High-density polyethylene without bran, however, the physical and mechanical properties are very different, which is one of the important contents of the chain structure in polymer physics]. On the other hand, the function of the chain transfer reaction is to reduce the average molecular weight of the polymer. Therefore, the purpose of controlling the molecular weight of free radical polymers can be achieved by adding compounds that are prone to chain transfer reactions. This is the molecular weight regulator, also known as Chain transfer agent, the two are universal. This is a very clear concept in polymer chemistry, and there are also very clear definitions in all polymer chemistry textbooks. The substances commonly used as molecular weight regulators are mercaptan organics that are prone to chain transfer reactions, such as dodecyl mercaptan, mercaptoacetate, etc. Due to the unpleasant odor and toxicity of mercaptan, in recent years, people have developed various alternative high-efficiency molecular weight regulators for mercaptan, such as α-methylstyrene linear dimer, etc.
Preparation
the steps for preparing the molecular weight regulator are as follows: 0.1g tetraethyl thiuram disulfide, 0.1g tetrapropyl thiuram disulfide, 0.2g tetrabutyl thiuram disulfide, 0.2g tetraisobutyl thiuram disulfide and 0.2g tetrapentyl thiuram disulfide are mixed to prepare the molecular weight regulator.