In polymer chemistry, the molar mass distribution (or molecular weight distribution) describes the relationship between the number of moles of each polymer species (Ni) and the molar mass (Mi) of that species. In linear polymers, the individual polymer chains rarely have exactly the same degree of polymerization and molar mass, and there is always a distribution around an average value. The molar mass distribution of a polymer may be modified by polymer fractionation.
Different average values can be defined, depending on the statistical method applied. In practice, four averages are used, representing the weighted mean taken with the mole fraction, the weight fraction, and two other functions which can be related to measured quantities:
Number average molar mass (M_n), also loosely referred to as number average molecular weight (NAMW).
Mass average molar mass (M_w), where w stands for weight; also commonly referred to as weight average or weight average molecular weight (WAMW).
Z-average molar mass (M_z), where z stands for centrifugation ().
Viscosity average molar mass (M_v).
Here, a is the exponent in the Mark–Houwink equation that relates the intrinsic viscosity to molar mass.
These different definitions have true physical meaning because different techniques in physical polymer chemistry often measure just one of them. For instance, osmometry measures number average molar mass and small-angle laser light scattering measures mass average molar mass. M_v is obtained from viscosimetry and M_z by sedimentation in an analytical ultra-centrifuge. The quantity a in the expression for the viscosity average molar mass varies from 0.5 to 0.8 and depends on the interaction between solvent and polymer in a dilute solution. In a typical distribution curve, the average values are related to each other as follows:
The dispersity (also known as the polydispersity index) of a sample is defined as Mw divided by Mn and gives an indication just how narrow a distribution is.
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Explores polymer synthesis basics, including step and radical chain polymerization, molecular weight control, copolymerization, and crosslinked polymers for microengineering.
Static light scattering is a technique in physical chemistry that measures the intensity of the scattered light to obtain the average molecular weight Mw of a macromolecule like a polymer or a protein in solution. Measurement of the scattering intensity at many angles allows calculation of the root mean square radius, also called the radius of gyration Rg. By measuring the scattering intensity for many samples of various concentrations, the second virial coefficient, A2, can be calculated.
Size-exclusion chromatography (SEC), also known as molecular sieve chromatography, is a chromatographic method in which molecules in solution are separated by their size, and in some cases molecular weight. It is usually applied to large molecules or macromolecular complexes such as proteins and industrial polymers. Typically, when an aqueous solution is used to transport the sample through the column, the technique is known as gel-filtration chromatography, versus the name gel permeation chromatography, which is used when an organic solvent is used as a mobile phase.
In chemistry, the dispersity is a measure of the heterogeneity of sizes of molecules or particles in a mixture. A collection of objects is called uniform if the objects have the same size, shape, or mass. A sample of objects that have an inconsistent size, shape and mass distribution is called non-uniform. The objects can be in any form of chemical dispersion, such as particles in a colloid, droplets in a cloud, crystals in a rock, or polymer macromolecules in a solution or a solid polymer mass.
Know modern methods of polymer synthesis. Understand how parameters, which determine polymer structure and properties, such as molecular weight, molecular weight distribution, topology, microstructure
The student has a basic understanding of the physical and physicochemical principles which result from the chainlike structure of synthetic macromolecules. The student can predict major characteristic
Introduction à la physique des polymères et aux liens entre structures chimiques et propriétés macroscopiques, avec accent sur la morphologie et le comportement thermomécanique. Méthodes de mise en œu
Ought to their bioinert properties and facile synthesis, poly[(oligoethylene glycol)methacrylate]s (POEGMAs) have been raised as attractive alternatives to poly(ethylene glycols) (PEGs) in an array of (bio)material applications, especially when they are ap ...
Thermoset rubbers give rise to elastomers with tunable stiffness and high resilience but are not recyclable. Thermoplastic elastomers can address this problem but their broad applicability is impeded by either limited operating temperatures or inferior ela ...
Communities are shared areas on the Zenodo platform where projects, institutions, domains, and conferences can curate and manage their research outputs. An EPFL community https://zenodo.org/communities/epfl was created in 2013, mainly as a light-weight sol ...