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Revolutionary discovery: How do chain transfer agents change polymerization reactions?
In polymerization chemistry, chain transfer reaction is an important polymerization reaction that can effectively change the properties of polymers, and especially occupies a core position in current polymerization research.
The basic process of a chain transfer reaction involves the reaction between a growing polymer chain and another molecule. Simply put, active centers are transferred from existing polymer chains to new molecules, a process that results in a reduction in the average molecular weight of the final polymer. Whether free-radical-based polymerization, ring-opening polymerization, or a variety of other polymerization types, chain transfer reactions are ubiquitous.
Chain transfer reactions often have a significant impact on polymerization reactions and are divided into several types.
Types of chain transfer
Chain transfer reactions are usually classified according to the molecular properties of the reaction, including the following:
- Transfer of chain transfer agents: This type of chain transfer agent usually contains at least one weak chemical bond, such as mercaptans and Halocarbons.
- Transfer to monomer: Chain transfer occurs when growing polymer chains extract atoms from unreacted monomers in the reaction medium.
- Transfer to polymer: During polymerization reactions, chain transfer may occur on existing polymer chains.
- Transfer to solvent: In solution polymerization, the solvent can also act as a chain transfer agent. If the selected solvent is not inert, low molecular weight polymers may be produced.
These different forms of chain transfer reactions provide various options for adjusting the properties of polymers, making them more flexible in industrial applications.
Historical development
The concept of chain transfer was first proposed by Hugh Stott Taylor and William H. Jones in 1930. The initial research focused on the production of polyethylene. They found that the characteristics of the polymerization reaction product could not be explained by traditional models, and proposed the concept of "transfer" to explain the reaction mechanism.
Flory incorporated the concept of chain transfer into his mathematical treatments in 1937, and went a step further to propose the term "chain transfer" to explain the phenomenon that the average length of polymer chains during polymerization is often lower than predicted.
During World War II, the American Rubber Reserve Company began to use chain transfer agents on a large scale, proving that this method can significantly affect the properties and production efficiency of polymers. With the passage of time, the research on chain transfer has become more and more in-depth, and a variety of mechanisms related to chain transfer reactions have been discovered, providing a solid foundation for polymer modification.
Current research activities
By the 1980s, the theory and applications of chain transfer reactions had matured and were widely documented in standard polymer chemistry textbooks. However, in particular, various forms of free radical living polymerization, such as catalytic chain transfer polymerization, RAFT, and iodine transfer polymerization (ITP), have become the focus of current research.
These studies show that chain transfer reactions can generate polymer chains with similar chain transfer activity while retaining the original chain transfer activity.
These different polymerization methods bring new possibilities to the development of polymer chemistry and further expand the application potential of chain transfer agents.
