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Exploring the secret world of polymers: Why is living cationic polymerization a win-win for both academia and business?
Living cationic polymerization is a technique that can produce highly regulated polymers, which has attracted great attention from both academia and the commercial community. This technology can not only synthesize polymers with low molecular weight distribution, but also produce very special polymer structures such as star polymers or block copolymers. This makes living cationic polymerization play an important role in current polymer research and development.
The key to living cationic polymerization is that it has a well-defined and controlled initiation and propagation process, while minimizing the possibility of side reactions, termination and chain transfer.
Technical foundation
In carbocationic polymerization, the active site is the carbocation, accompanied by a nearby counterion. Its basic reaction steps are: when monomer A comes into contact with monomer B, a polymerization chain is formed through a specific chemical reaction. In this process, the control of chain amplification, chain transfer and chain termination is crucial. Ideally, the rate of exchange between the chemical equilibrium of the active ionic polymer species and the stationary covalent species is faster than the rate of polymerization.
The monomers used in the polymerization reaction are extensive, including vinyl ether, α-methyl vinyl ether, isobutylene, styrene and N-vinylbenzothiazole.
History
The development of living cationic polymerization began in the 1970s and 1980s, with notable researchers such as Higashimura and Sawamoto performing key experiments in multiple polymerization systems that advanced the technology. During this period, the academic community first discovered a method of polymer synthesis using iodine and acid as initiators, which led to the macro-engineering process of polymers.
Isobutylene polymerizationLiving isobutylene polymerization is usually carried out at below 0 °C in a mixed solvent system containing a nonpolar solvent such as hexane and a polar solvent such as chloroform or dichloromethane. In this process, the initiator can be alcohol, halogen or ether, and the co-initiator includes boron chloride and the like. The successful polymer modulus can reach 160,000 g/mole and the polydispersity index can be controlled to 1.02.
Alcohol ether polymerization
Alcohol ethers (e.g., CH2=CHOR type) have been extensively studied as very reactive monomers in living cationic polymerization. Related systems are mostly based on iodine and hydroiodic acid and involve catalysts such as zinc chloride.
Ring-opening polymerization
In living cationic ring-opening polymerization, the monomer is usually a heterocyclic molecule such as epoxide or tetrahydrofuran. The propagating species in this process is not a carbon cation, but an oxonium ion. However, its termination is relatively difficult and often occurs due to nucleophilic attack by the growing polymer chain. For this type of polymerization, initiators with strong electron affinity such as trifluorinated acid are often used.
In the process of life aggregation, how to balance aggregation and termination is the key to success or failure.
From the perspective of commercial value, living cationic polymerization has not only led to an increase in the market demand for precisely controlled polymer products, but also made the application of many emerging materials possible due to its technological maturity and stability. Future polymer research also faces many new challenges, including how to further improve the efficiency and selectivity of polymerization reactions. At the same time, as a constantly innovative technology, whether living cationic polymerization will become a catalyst for future industrial changes will be a question worth pondering?
