Branching density

The gas branch densities along coexistence, evaluated for the bulk systems A3 and 10, are pg g = 0.046 0.001 and pgag = 0.0237 0.005, respectively. The system A3 is weakly associated however, in the system 10 the gas phase remains weakly associated. On the other hand, association in the liquid phase is significant and greater than 80% [41]. 

In Figure 6, these data are plotted versus the branching density z of crosslinking molecules. Gy./G is fairly independent of network microstructure. It covers a range of 0.24 to 0.32 as a result of statistical scattering, averaging to 0.28 as in case of the networks with tetrafunctional crosslinks. 

On the contrary, are(j u/0red clearly shows some dependence on the structure of the crosslinks, changing from around 0.27 to 0.10 as the branching density z increases from 0.01 to 0.5. The different time scale of the experiments can not have effected the results, because is was proved that G is independent of frequency. The deformation ratio X is 1.00005 in case of torsional vibrations and 1.02-1.04 in case of uniaxial extension. Hence it ap-... 

Figure 6. Relative energy part of the modulus at 298 K versus branching density z. Key , vred.v/

As pointed out in the first part of this work, tetrafunctionally crosslinked PDMS also shows some dependence of the energy part of the modulus on network density and on the measuring method, but the effects observed there, are much smaller than the great variation of /a with branching density in case of networks... 

The moduli, measured at crosslinking temperature T, which are given in the last two columns of Table IV, are abou two to three fold greater than those computed from phantom theory. Except for the samples with the lowest branching densities, the observed values agree satisfactorily with those for an affine network. 

The remaining question is, how the deviations from phantom network theory at high branching densities can be explained. 

Figure 7. Ratio of experimentally observed and theoretically calculated modulus, using phantom network theory with f2 and v2, versus branching density z-...

Ionkin has reported a similar series of Ni(II) catalysts 1.50a and b bearing ortho-difuryl substituents that are noteworthy for their high thermal stability [127], The bulkier benzofuranyl-substituted catalyst 1.50b possesses the most attractive catalytic properties (Table 5, entry 9) the ability to form high molecular weight polymers (albeit in high polydispersity) and reasonable activity even at 150 °C. Even under these harsh conditions, the polymer branching density is still relatively low. 

Ionizing radiation. Further studies on the effects of ionizing radiation such as 60Co y-ray radiation and ion beams on polysilanes have been reported.295 304-306 Both positive and negative resist properties can be shown, depending on the side-chain type, branch density, and the presence or absence of radical initiators. 

The synthetic approach used for dendrigraft-po y(butadicncs) has the potential to provide control over the composition and architecture of the molecules. The branch molecular weight is easily varied with the amount of initiator used in the polymerization reaction. Solvent polarity control in the polymerization allows variation of the proportion of 1,2-units in the side chains, and hence the branching density. 

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