Molekulatömegátlagok

Molekulatömegátlagok, commonly referred to as molecular weight averages, are important parameters used to describe the size distribution of polymers. Polymers are long chains made up of repeating smaller units called monomers. In a real sample of a polymer, the chains are not all the same length. This variation in chain length leads to a distribution of molecular weights. Molecular weight averages provide a single numerical value that represents the typical molecular weight of the polymer chains in a sample.

Several types of molecular weight averages exist, each emphasizing different aspects of the distribution. The number-average molecular weight (Mn) is the total weight of all polymer chains divided by the total number of polymer chains. It is calculated by summing the molecular weights of each individual chain and dividing by the total number of chains. The weight-average molecular weight (Mw) gives more weight to larger molecules. It is calculated by summing the product of the molecular weight of each chain and its weight fraction, then dividing by the total weight fraction. Another important average is the Z-average molecular weight (Mz), which gives even more weight to very large molecules.

The ratio of Mw to Mn, known as the polydispersity index (PDI), is a measure of the breadth of the molecular weight distribution. A PDI close to 1 indicates a narrow distribution, meaning most polymer chains have similar lengths. A higher PDI suggests a broader distribution with a significant range of chain lengths. These averages are crucial for understanding and predicting the physical and mechanical properties of polymers, such as their viscosity, strength, and processing behavior. Different applications may require polymers with specific molecular weight distributions.