kjedeoverføringsagent

A kjedeoverføringsagent, often translated as chain transfer agent, is a substance used in free radical polymerization. Its primary function is to control the molecular weight of the polymer being produced. This is achieved by interrupting the growth of a polymer chain and initiating a new one.

During free radical polymerization, monomer units add sequentially to a growing polymer chain. A kjedeoverføringsagent reacts with this growing chain, abstracting an atom or group from it. This action terminates the growth of that particular polymer chain. Simultaneously, the agent, now itself a radical, can initiate the polymerization of a new monomer unit, starting a fresh polymer chain.

The effect of a kjedeoverføringsagent is to reduce the average molecular weight of the polymer. By providing more initiation sites, it leads to a larger number of shorter polymer chains. The effectiveness of a kjedeoverføringsagent is quantified by its chain transfer constant, which indicates its relative tendency to participate in chain transfer compared to monomer addition.

Common examples of kjedeoverføringsagenter include thiols, such as dodecyl mercaptan, and some halogenated compounds. The choice of agent depends on the specific monomer, initiator, and desired polymer properties. Precise control over molecular weight is crucial for tailoring polymer characteristics like viscosity, mechanical strength, and solubility for various applications.