Scaling Parameters for the Number MWD

In order to scale the number MWD correctly, the values of [i ]o and [i ]res must be known. As explained in the previous chapter, this can be accomplished by using good estimates for Df and average kt values. As we are working at very low conversions, both parameters will be estimated for the case of a bulk monomer solution in which no polymer is present. 

Accurate values of k] for the acrylates that are being studied here, are not directly available from literature. Fischer and Paul [35], however, have shown that this rate coefficient can be predicted reliably by the Smoluchowski equation, provided that the 

Here is the monomer diffusion coefficient of an acrylate in bulk monomer and 

V acrylate the bulk monomer viscosity of the acrylate. Equation 4.15 is an approximation as the diffusion coefficient of a diffusing entity does not only depend upon the viscosity of the medium, but also on the charateristics of the dififusant itself At 50°C, the monomer diffusion coeficient of MMA is relatively well determined and has been found to be equal to 4.11TO m s [36]. The viscosities of MMA, MA, EA and BA, that are needed to estimate a diffusion coefficient for these monomers on the basis of equation 4.15, were calculated according to [37]  

Viscosities are expressed in centipoises and T is the absolute temperature. For the estimation of the capture radius, not the monomer MMA, but the monomer styrene was used (for geometric reasons). The capture radius of all acrylates was therefore set equal to 3-10 ° m [38, 39], irrespective of the temperature studied. Using all of the above equations, in conjunction with the Smoluchowski equation  

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