Intramolecular repulsions

A commercially important example of the special case where one monomer is the same in both copolymers is blends of styrene—acrylonitrile, 1 + 2, or SAN copolymers with styrene—maleic anhydride, 1 + 3, or SMA copolymers. The SAN and SMA copolymers are miscible (128,133,144) so long as the fractions of AN and MA are neatly matched, as shown in Figure 4. This suggests that miscibility is caused by a weak exothermic interaction between AN and MA units (128,133) since miscibility by intramolecular repulsion occurs in regions where 02 7 can be shown (143) by equation 11. 

Viscosimetric studies of organotin copolymer solutions allow the changes in the shape of the macromolecules to be followed as a function of the electrostatic charge. From the plot of the intrinsic viscosity of copolymers in DMFA solution against the degree of dilution it is seen that increasing dilution results in a rise of viscosity, probably due to an extension of macromolecular chains accompanied by conformational transformations. Naturally, this rise in viscosity with dilution cannot proceed infinitely since a coiled chain cannot be extended more than a completely extended chain conformation, due to intramolecular repulsion. 

Despite some lack of physical meaning, the empirical Laidler terms have a rather successful predictive power. That justified their use in the past as replacements for Es values [85,86,88], when computational methods were not readily available. It also justifies recent efforts to develop the Laidler scheme by using a larger number of parameters (accounting, e.g., for intramolecular repulsions) [92],... 

The ground state geometries in these complexes are often determined by a subtle balance of the energy released by an increase in coordination number and the energy lost by intramolecular repulsion. The question of versus bonding in the tris(cyclopentadienyl)uranium aUyls is one molecular example. The structures of the lanthanide tiicyclopentadienides represent another example in extended crystalline arrays. 

The observed stereochemical variation (equation 8) was ascribed to the increasing intramolecular repulsive interactions, X X for example, when bulkier phosphines and heavier halides were introduced. Based on measurements of molecular species in solution, it was further proposed that a step involving dissociation into two dimeric molecules may occur for extremely bulky ligands.174... 

Unfavourable intramolecular repulsions between NH+ groups are highly dependent on the distance between the protonation sites and thus the introduction of a longer, propylenic spacer generally increases the second and subsequent basicity constants as well as influencing the first by increased electron donation. Compare entries 3 and 4 in Table 3.16. The effect is also evident in the linear... 

Miscibility windows originate from a delicate balance of inter- and intramolecular repulsions. Figure 8 gives an example. The corresponding homopolymers are immiscible, but, not so PPO and the random copolymers in a certain range of copolymer composition. Experimentally determined miscibility windows are listed in Table 3. 

The CN groups assume varying angles with regard to the helical axis, guided by intramolecular repulsion and intermolecular attraction. In the unstrained state, two... 

What can be expected, if such molecules are introduced into the fiber The more mobile additive molecules have a greater chance to approach PAN — CsN dipoles in the most favorable direction (cf. Eq. 1) the intramolecular repulsion of adjacent — CsN groups within the polymer molecules will be partly neutralized , with the result of less resistance to an imposed stress. At the same time, part of the intermolecular dipole-dipole interactions between polymer molecules will be replaced by interactions of polymer CN groups with dipoles of the additive, which again results in reduced tensile strength. On the other hand, the presence of the plasticizing compound evidently provides increased mobility for the individual segments of the polymer molecules. 

That the importance of intramolecular repulsions is still not generally recognized is because intramolecular distances are usually compared with the sum of the Bartell... 

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