Polymer’s molecular weight

Polymer-Fluid Equilibria and the Glass Transition Most polymer systems fall in the Class HI or Class V phase diagrams, and the same system can often change from one class into the other as the polymer s molecular weight changes. Most polymers are insoluble in CO9 below 100°C, yet CO9 can be quite sohible in the polymer. For example, the sorption of CO9 into silicone rubber is highly dependent upon temperature and pressure, since these properties have a large influence on the density and activity of CO9. 

The term stepwise kinetics, or step-growth kinetics, refers to polymerizations in which the polymer s molecular weight increases in a slow, stepwise manner as reaction time increases. 

Determination of a Polymer s Molecular Weight Distribution by Analytical Ultracentrifugation... 

SiLK resin is a solution of low molecular weight, aromatic, thermosetting polymer. The polymer s molecular weight and solution concentration were tuned to enable precise and convenient deposition by spin coating, a technique universally used by the industry for the deposition of photoresist materials. After deposition on a wafer, the polymer is thermally cured to an insoluble film that has a high glass transition temperature. The polymer has good mechanical properties at process temperatures, which is required for the application, and it is also resistant to process chemicals. 

A measure of the broadness of a polymer s molecular weight distribution is the polydis-persity index defined by... 

The last two are the result of a reduction in the polymer s molecular weight. It is also interesting that degradation occurs to some degree immediately after the commercial polymer is produced. It can occur during various phases of the polymer s life cycle ... 

Viscosity measurements alone cannot be directly used in the Mark-Houwink-Sakurada equation to relate absolute viscosity and polymer molecular weight, since additional unknowns, K and a must be determined. Therefore, viscometry does not yield absolute molecular weight values it rather gives only a relative measure of polymer s molecular weight. Viscosity measurements based on the principle of mechanical shearing are also employed, most commonly with concentrated polymer solutions or undiluted polymer these methods, however, are more applicable to flow properties of polymers, not molecular weight determinations. 

For typical thermal plastic, not only the viscosity has temperature dependence, but it also strongly depends on the polymer s molecular weight relative to the so-called critical molecular weight of a given polymer M. can be interpreted as the molecular weight at which a temporary network of entanglements... 

J J Meister, E G Richards. Detemination of a polymer s molecular weight distribution by analytical ultracentrifugation. In W G Glasser, S Sarkanen, eds. Lignin, Properties and Materials. Washington, DC Am Chem Soc, 1989, pp. 58-81. 

Polyelectrolytes raise the viscosity of aqueous solutions thus acting as thickeners, and the magnitude of the effect increases with the polymer s molecular weight. Naturally occurring gums... 

One of the most important properties in condensation polymers is the polymer s molecular weight. Consider a linear step-growth polymerization of AB-type monomers. For illustrative purpose, let A refer to a hydroxyl group and B to a carboxyhc add group, so that a polyester is formed. The polymerization reaction is ... 

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