Molecular weight dispersity

Fig. 22. The effect of solvent composition on the molecular weight ( ), conversion (O), and molecular weight dispersity ( ) of PaMeSt prepared using the HSi(CH3)2CH2CH2

The effect of changing solvent composition (polarity) on molecular weight dispersity is noteworthy. Mw/Mn is quite low (1.69) in the experiment carried out by the use of 100% CH2C12 and it increases monotonically with increasing n-C6H14 content. It is very difficult to interpret these data at this time. 

Aqueous Drilling Muds Low-Molecular-Weight Dispersants... 

It was suggested in a previous publication (9) that flocculation at the UCFT can be ascribed to the free volume dissimilarity between the polymer stabilizing the particle and the low molecular weight dispersion medium. Incorporating this idea in a quantitative way into the theory of steric stabilization allowed for a qualitative interpretation of the experimental data. This idea is further extended to include the effect of pressure on the critical flocculation conditions. 

Gel electrophoresis is widely used in the routine analysis and separation of many well-known biopolymers such as proteins or nucleic acids. Little has been reported concerning the use of this methodology for the analysis of synthetic polymers, undoubtedly since in many cases these polymers are not soluble in aqueous solution - a medium normally used for electrophoresis. Even for those water-soluble synthetic polymers, the broad molecular weight dispersities usually associated with traditional polymers generally preclude the use of electrophoretic methods. Dendrimers, however, especially those constructed using semi-controlled or controlled structure synthesis (Chapters 8 and 9), possess narrow molecular weight distribution and those that are sufficiently water solubile, usually are ideal analytes for electrophoretic methods. More specifically, poly(amidoamine) (PAMAM) and related dendrimers have been proven amendable to gel electrophoresis, as will be discussed in this chapter. 

This section describes the synthesis of oxazolidine esters used as polymer hardeners that cannot be synthesized using chemical catalysis, the synthesis of polyurethane polymers with methods that avoid the use of isocyanates and the enzymatic synthesis of polyesters with low molecular weight dispersity. 

Vakhtina, I. A. et al. A Study of the Functionality and Molecular Weight Dispersity for Stiff Foams, in Sintez i fiziko-khimiya polimerov (Synthesis and Physico-Chemistry of Polymers), p. 58, Kiev, Naukova dumka, 1976... 

A colloid is a small particle separated from others by a dispersion medium (in aqueous systems this medium is obviously water). The size of colloidal particles ranges from one nanometer (nm) to one micrometer (pm). They are formed either by aggregates of small molecules or by large molecules of high molecular weight. Dispersions created with coarser materials (< 10 pm) are sometimes considered colloidal dispersions as well. 

The Effect of Experimental Conditions on Molecular Weights and Molecular Weight Dispersities GPC Studies... 

Controlled/ living radical polymerization (CLRP) processes are well-established synthetic routes for the production of well-defined, low-molecular weight-dispersity polymers [99]. The types of CLRP processes (initiator-transfer agent-terminator (INIFERTER), atom transfer radical polymerization (ATRP), nitroxide-mediated radical (NMRP) polymerization, reversible addition-fragmentation transfer (RAFT)) and their characteristics are described in Section 3.8 of Chapter 3 and in Section 14.8 of Chapter 14. 

Hint 1. If what controls the instantaneous MWD is independent of reaction time or conversion, then the final product will have the most probable (or Flory-Schulz) distribution with a molecular weight dispersity (polydispersity) of 2 (for isothermal operation). 

Figure 15.5 Effect of molecular weight dispersity ( )) (formerly known as polydispersity) using schematic Gibbs triangle diagrams for polymer-solvent system, generation of cloud point curve and shadow curve in temperature-composition diagram.

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