Geometric molecular weight distribution

FIGURE 1.5 Geometric molecular weight distribution at different conversions. (See insert for color representation of the figure.)... 

Experimentally, as indicated in Fig. 12.13, we find that D/Dq depends on the shear stress at the wall xw (a flow variable) and the molecular weight distribution (MWD) (a structural variable) (22). The length-to-diameter ratio of the capillary (a geometric variable) also influences D/Dq. The swelling ratio at constant xw decreases exponentially with increasing L/Dq and becomes constant for L/Dq > 30. The reason for this decrease can be explained qualitatively as follows. Extrudate swelling is related to the ability of polymer melts and solutions to undergo delayed elastic strain recovery, as discussed in... 

The influence of catalyst supports is being widely studied at present. Metal complexes or clusters are applied un supports like silica, alumina or zeolites [42, I30[. Tliesc supports influence the molecular weight distribution, not only by their acidic or basic properties but also by their ability to stabilize metal dispersions and by their geometric properties. 

More complex chemical systems lead to molecular weight distributions that are qualitatively similar linear polycondensations have most often geometrical or nearly geometrical distributions with polydispersities Ma,/M close to 2, whereas nonlinear polycondensations lead to extremely broad distributions near the gel point, but always dominated in number and even in weight by the lower molecular weight species. 

Figure 1.4 shows the chain length distribution for a geometric distribution for different values of p, while Figure 1.5 shows the corresponding molecular weight distribution (without taking into account the mass loss due to the condensate). 

Physical adsorption refers to attraction and bonding of the adsorbate onto a surface and may result from physical interaction with the surface. In physical adsorption, the forces involved are intermolecular ones, such as van der Waals forces. Certain specific molecular interactions arise from particular geometrical or electronic properties of the adsorbent and physical adsorption of long polymer chains to the surface can help in attaching polymer chains of well-defined length, molecular weight distribution, and composition. 

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