Critical molecular weight measurement

The polyethylene linewidths, as illustrated in Fig. 1, clearly indicate that a constant value is attained in the melt between 1-8 X 10. Proton T2 measurements at 150°C indicate that there is a change in slope in this quantity as a function of molecular weight at about = 6 x 10. ( ) The critical molecular weight as determined from bulk viscosity measurements for this polymer has been given as 2 x 10 ( ) and 3.8 x 10. (5 ) These values are very close to those which would be deduced from the linewidth measurements. For polydimethyl siloxane the break in the proton T2-molecular weight curve occurs at about M = 5 x 10. (37) is about 2.5 x 10 from viscosity measurements. ( ) Fig. 5... 

Inoue T, Okamoto H, Osaki K (1991) Birefringence of amorphous polymers. 1 Dynamic measurements on polystyrene. Macromolecules 24 5670—5675 Isayev AI (1973) Generalised characterisation of relaxation properties and high elasticity of polymer systems. J Polym Sci A-2 116 2123—2133 Ito Y, Shishido S (1972) Critical molecular weight for onset of non-Newtonian flow and upper Newtonian viscosity of polydimethylsiloxane. J Polym Sci Polym Phys Ed 10 2239— 2248... 

Data for the Me of polymers [16] are listed in Table 11.4. Me can be predicted by using two different correlations, as discussed below. Both of these predictions can differ significantly from "observed" values of Me deduced from measured GN°(T) values by using Equation 11.23. 1. Me can be assumed to be equal to half of the "critical molecular weight" Mcr, which will be discussed further in Chapter 13. 

M is determined exactly from the repeat unit composition. The repeat unit length can be measured by using an interactive molecular modeling program. The rotational degrees of freedom of the backbone can be counted by using the rules provided in Section 4.C. The new quantitative structure-property relationships developed in this book for V and p (Chapter 3), Ecoh (Chapter 5), Tg (Chapter 6), critical molecular weight (Equation 11.25 combined with Equation 11.24), molar Rao function (Section ll.B), molar Hartmann function (Section ll.B), characteristic ratio (Chapter 12), and surface tension (Chapter 7), allow the application of various derived correlations for mechanical properties to all polymers built from the nine elements (C, N, O, H, F, Si, S, Cl and Br) included in the scope of our work. 

It will be shown in Chapter 13 that information gained from solution viscosity measurements under 0 conditions can also be used to predict the critical molecular weight Mcr. Mcr is... 

A critical molecular weight of approximately 20 000 can be derived from the dependence of Tjo and Afw for the silicone oils studied (Fig. 3). This fact is less pronounced in a TV-Af plot (Fig. 2). For a rough estimate of the molecular weight the simple potential fit in Fig. 2 can be used. Due to the existence of the critical molecular weight, however, a piecewise fitting of the low and high molecular parts of the curve is recommendable. The T2 experiment should be performed at temperatures sufficiently below 0 °C to increase the accuracy of the measurement. 

Table 3 Comparison of the Zero Strength Molecular Weight Mq Measured in Flexure with the Critic Molecular Weight at which Entanglements are Obtained Mg, Measured using Melt Viscosity ...

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