HighMolecularWeight

High molecular weight (HMW) is a term used to describe macromolecules whose molecular weights exceed those of typical low molecular weight species in the same context. In polymer science, high molecular weight is defined relative to the material and measurement method rather than by a universal threshold. As a rule of thumb, polymers with weight-average molecular weight Mw around or above 100,000 g/mol (100 kDa) are commonly regarded as high molecular weight, although some applications may consider higher Mw necessary for certain properties. The concept also applies to biopolymers such as proteins, polysaccharides, and nucleic acids, where higher Mw often correlates with increased persistence, viscosity, or entanglement.

Measurement and characterization: Molecular weight for polymers is typically determined by gel permeation chromatography (GPC, also called SEC) with calibration against standards, and can be supplemented by multi-angle light scattering (MALS) or viscometry. The polydispersity index (PDI = Mw/Mn) describes the breadth of the distribution and affects processing and properties.

Effects on properties: Higher Mw generally increases solution and melt viscosity and the elastic modulus, promotes chain entanglements, and improves mechanical strength and thermal resistance. It can also reduce chain mobility and solubility, complicating processing and blending. The impact depends on architecture (linear vs branched), tacticity, and end groups.

Applications and notes: HMW polymers are common in fibers, films, and high-performance materials; in biomedicine, high Mw can influence network formation in hydrogels or affect diffusion and bioactivity. For biopolymers, very high Mw may increase aggregation or immunogenicity in some contexts.