highermolecularweight

Higher molecular weight, commonly referred to as high molecular weight, describes molecules whose molar mass is greater than a reference value. In chemistry, the term is most often used for polymers, where average molecular weights are reported as Mn (number-average) and Mw (weight-average), and the ratio Mw/Mn is the polydispersity index (PDI). Higher molecular weight implies longer chains or larger assemblies, which influence how a substance behaves in solution and in solid form.

Measurement of molecular weight depends on the material. Small molecules are typically characterized by mass spectrometry. For polymers, gel permeation chromatography (GPC/SEC) is widely used, often with light scattering or refractive-index detectors to determine Mw. Absolute Mw can be obtained by light scattering methods or osmometry. Mn and Mw, along with PDI, help describe distribution of chain lengths in a sample.

Higher molecular weight generally increases solution viscosity and can raise glass-transition or melting temperatures. In polymers, large Mw often improves tensile strength and toughness but can reduce solubility and processability due to chain entanglement. In biological macromolecules, higher Mw can slow diffusion and alter pharmacokinetic properties.

In applications, higher molecular weight materials are common in plastics, elastomers, and biotherapeutics. Understanding Mw and PDI is essential for predicting performance, processing behavior, and biological interactions. The choice of Mw depends on the balance between desired strength, solubility, manufacturability, and delivery considerations.