Melt viscosity molecular weight dependence

Figures 8 and 9 show the dependence of the self-diffusion constant and the viscosity of polyethylene melts on molecular weight [47,48]. For small molecular weights the diffusion constant is inversely proportional to the chain length - the number of frictional monomers grows linearly with the molecular weight. This behavior changes into a 1/M2 law with increasing M. The diffusion...

Zhu D, Haidekker MA, Lee J-S, Won Y-Y, Lee JC (2007) Application of molecular rotors to the determination of the molecular weight dependence of viscosity in polymer melts. Macromolecules 40 7730-7732... 

As known from the broad crossover phenomena observed in the macroscopic chain dynamics (such as the molecular weight dependence of the melt viscosity) very important limiting mechanisms must exist that affect the confinement limit of the reptation process. These processes increase in importance as the chain length decreases. The two main mechanisms are [62] ... 

Considering the development of the theory of melt viscosity, one notices a similar kind of evolution as with the intrinsic viscosity of dilute solutions. In both cases starting points were formed by empirical relations describing the respective molecular weight dependencies. Only afterwards, the relations are interpreted on more fundamental grounds. 

The molecular meaning of b is best seen from the second or third equality of Eq. (3). In other words, b is explicitly related to the steady shear melt viscosity q and depends on the chain-chain interactions near the melt/wall interface as quantified by the friction coefficient p. In the limit of no polymer adsorption or in absence of interfacial chain entanglements due to the coil-stretch transition, P involves an interfacial viscosity q , which is as small as the viscosity of a monomeric liquid and independent of the molecular weight Mw p=qj/a, where a is a molecular length. Thus at the stick-slip transition, the molecular weight dependence of b arises entirely from q in Eq. (3). 

A more quantitative interpretation of the scattering data involves molecular models. As an example, we turned to the Rouse model [20] developed for solutions and extended to melts [21]. As this model is unable to account for the molecular weight dependence of zero-shear viscosity (t o M ) above the critical molecular weight (Mc 35 000 for PS), the analysis wall be extended as a next step to other models which are more realistic for entangled systems. A basic result of the Rouse model relates the monomeric friction coefiBcient Co and the zero-shear viscosity t o ... 

Teramoto, a., and H. Fujita Temperature and molecular weight dependence of the melt viscosity of polyethylene oxide in bulk. Makro. Chemie 85, 261 (1965). 

The viscosities of polymer solutions and of polymer melts have some very important common features, which are related to the fundamental nature of the motions of polymer chain segments [4,8,10] resulting in the flow of macromolecular chains. At an empirical level, one manifestation of these interrelationships is that Mcp which is the key material parameter determining the molecular weight dependence of the melt viscosity, can be estimated from the intrinsic viscosity of the polymer under 0 conditions, which was discussed in Chapter 12. If K -Mci.0-5 is expressed in units of cc/grams, then Mcr can be predicted [7] (but only to within a factor of two) by using Equation 13.6. 

Step 22. Calculate the viscosity of a polymer melt and/or the zero-shear viscosity of a concentrated polymer solution. The molecular weight dependence of the zero-shear viscosity is given by equations 13.2 and 13.3, where the critical molecular weight Mcr (Equation 13.6) is... 

Figure 3-26. The molecular-weight dependence of the viscosities of a series of polyethylene melts. It can be seen that the slope of 3 predicted by equation (3-115) falls short, while a slope of 3.4 is virtually perfect. (Data from various sources.)...

The melt viscosity of PVC depends on the degree to which the particle structure is retained, as well as on the molecular weight. Consequently, a... 

Figure 4. (a) Inherent viscosity dependence of the melting temperature (r ) and the clearing temperature (T ) of nematic poly(2-n-decyl-1,4-phenylene-terephthalate) [6] and (b) the molecular weight dependence of the glass transition temperature (Lg) of nematic poly(2,2 -dimethyl-4,4 -biphenylene-phenyltereph-thalate)[7]. 

Most often the average molecular weight is used in relation to rheological properties (Berry and Fox, 1968), although this is only an approximation. When model blends are prepared by mixing monodisperse polymers, the molecular weight dependences are complicated. For example, the melt viscosity is less than the value predicted assuming t] is determined by My, (Watanabe et al., 1995 Monfort et al., 1984 Plazek et al., 1991). 

These features show striking similarities between ring and linear polystyrenes with respect to the molecular weight dependence of melt viscosity. Of especial interest is the virtual agreement of r/(r) and i] ) in entangled systems, i.e., in... 

Shear viscosity measurements on elastomers and polymer melts began with Mooney [M41] in 1936 and continued in the 1940s. Early measurements focused on molecular weight dependence and the dependence of the shear viscosity on shear rate. 

That the steady-state compliance is independent of the molecular weight is in agreement with experimental results (Fig. 7.S). On the other hand, the experimental exponent in the molecular weight dependence of Tmax and Vo is slightly larger than 3, ranging from 3 to 3.7. An example of the viscosity in melts is ven in Fig. 7.6. The reason for die discrepancy will be disrassed later. 

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