Kjedeutvidelse

Kjedeutvidelse, or chain extension, is a process used in polymer chemistry to increase the molecular weight of a polymer by linking shorter polymer chains together. This is typically achieved by reacting the polymer chains with a difunctional or multifunctional monomer or oligomer. These reactive molecules act as bridges, connecting the ends of the existing polymer chains. The goal is to form longer, more robust macromolecules.

This technique is particularly useful for polymers that are initially synthesized at a relatively low molecular weight, making them difficult to process or lacking desired physical properties. By extending the chain length, the resulting polymer often exhibits improved mechanical strength, increased viscosity, and enhanced thermal stability.

Common applications for chain extension include the production of polyurethanes, polyesters, and polyamides. In polyurethane manufacturing, for example, short-chain diols or diamines are reacted with isocyanate-terminated prepolymers to create higher molecular weight polyurethanes with tailored properties for foams, elastomers, and coatings. Similarly, chain extension can be employed to enhance the properties of recycled plastics, allowing them to be reprocessed into more durable products. The choice of chain extender and reaction conditions are critical to control the extent of extension and the final properties of the polymer.