Molecular weights effect

Concentration and Molecular Weight Effects. The viscosity of aqueous solutions of poly(ethylene oxide) depends on the concentration of the polymer solute, the molecular weight, the solution temperature, concentration of dissolved inorganic salts, and the shear rate. Viscosity increases with concentration and this dependence becomes more pronounced with increasing molecular weight. This combined effect is shown in Figure 3, in which solution viscosity is presented as a function of concentration for various molecular weight polymers. 

Experimental values of X have been tabulated for a number of polymer-solvent systems (4,12). Unfortunately, they often turn out to be concentration and molecular weight dependent, reducing their practical utility. The Flory-Huggins theory quahtatively predicts several phenomena observed in solutions of polymers, including molecular weight effects, but it rarely provides a good quantitative fit of data. Considerable work has been done subsequentiy to modify and improve the theory (15,16). 

Fig. 7. Model for PVC fusion, accounting for molecular weight effects and processing temperature effects (a) unfused PVC primary particles (b) partially melted PVC primary particles (c) partially melted then recrysta11i2ed high molecular weight PVC, showing strong three-dimensional stmcture and (d) partially melted then recrysta11i2ed low molecular weight PVC, showing weak three-dimensional stmcture.

Molecular weight, effect on centrifugal sizing, 159 Mollier charts, 27 Monitoring system, 356 Motor, 146 enclosure, 260 equations, 267 insulation, 257 locked rotor torque, 270 selection, 270 service factor, 262 starting characteristics, 270 starting time, 273, 274 synchronous vs induction, 265 variable frequency drives, 27/, 280 voltage, 258 Motors... 

Creton, C., Brown, H.R. and Shull, K.R., Molecular weight effects in chain pull-out. Macromolecules, 27, 3174-3183 (1994). 

For describing the observed molecular weight effects in chemical gels, we propose to distinguish three regions based on the precursor molecular... 

The initial melt of Ciooo was cooled down to various crystallization temperatures. Typical developments of crystalline domains at 370 K are shown in Fig. 37 here again the lamellae with the marked tapered shape are observed. Quite surprising is that the crystallization of Ciooo is rather fast in spite of the much longer chains. Any growth of lamellae of Ciooo at the temperature of 370 K, where Cioo did not show any appreciable growth, will be an indication of the molecular weight effect. 

Equation (5.42a) clearly depicts what determines P2, and indeed it appears that the average molecular weight of the unbumed gas mixtures is a major factor [16]. A physical interpretation as to the molecular-weight effect can be... 

We have made no detailed or systematic comparisons of molecular weight effects. 

All polymer chemists know this technique as cross-linking. It is the process of building intermolecular bridges. If two adjacent polymer molecules of equal size are connected by a cross-link, the molecular weight effectively doubles. From a... 

In solution, the two end chromophores of a polymer chain produce a molecular-weight effect even without energy migration, because the end rings have only one neighbor and thus yield fewer excimers than the middle chromophores. The probability M for an aryl vinyl polymer with N repeat units is given by... 

Fig. 22. Molecular weight effect of synthetic polymer adsorption. Molecular weight (MW) distribution of poly(vinyl chloride) in solution and in the adsorbed layer at equilibrium. Note that the adsorbed material has a higher average MW than the bulk solution (from Ref.1001, p. 120)...

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