Segmental mobility effect

In addition to the mobility of colloidal-sized probes, there is considerable interest in monitoring the motion of small molecules, including the solvent itself and also dye molecules. Once again, more is known about such mobilities in the case of transient gels, where it is now certain that "monomer segment mobility" effects are prerequisite to a correct dynsumical interpretation (102-105). Several papers in the present volume... 

Its plasticising effect on some polymers which increases segmental mobility and enhances the value of the dielectric constant of the polymer itself. 

It hag been shown that transition of a backbone carbon from the sp to sp state is promoted by tensile stresses and inhibited by compressive strains (10,44). The acceleration of the process of ozone oxidation of the polymers under load is not associated with the changes in supramolecular structure or segmental mobility of the chain. The probably reason of this effect is a decreasing of the activation energy for hydrogen abstraction (44). The mechanism of initial stages of the reaction of ozone with PP can be represented as ... 

Diffusion of small molecular penetrants in polymers often assumes Fickian characteristics at temperatures above Tg of the system. As such, classical diffusion theory is sufficient for describing the mass transport, and a mutual diffusion coefficient can be determined unambiguously by sorption and permeation methods. For a penetrant molecule of a size comparable to that of the monomeric unit of a polymer, diffusion requires cooperative movement of several monomeric units. The mobility of the polymer chains thus controls the rate of diffusion, and factors affecting the chain mobility will also influence the diffusion coefficient. The key factors here are temperature and concentration. Increasing temperature enhances the Brownian motion of the polymer segments the effect is to weaken the interaction between chains and thus increase the interchain distance. A similar effect can be expected upon the addition of a small molecular penetrant. 

The mole fraction of the monomer units that are cross-linked in the polymer is X,., and nt is Ihe number-average number of atoms in the polymer backbone between cross-links. The temperature should be expressed in absolute degrees in this equation. The constant K is predicted to be between 1.0 and 1.2 it is a function of the ratio of segmental mobilities of cross-linked to uncross-linked polymer units and the relative cohesive energy densities of cross-linked and uncross-linked polymer (88). The theoretical equation is probably fairly good, but accurate tests of it are difficult because of the uncertainty in making the correction for the copolymer effect and because of errors in determining nf. 

This paper presents new data on dissolution kinetics. The effects of alkali concentration, size of the cation, and salt addition were studied. The influence of segmental mobility on dissolution was elucidated by measuring the temperature coefficients of the dissolution rates. Experiments were also carried out to study the relation between the chemical structure of a polymeric Inhibitor and Its effectiveness 1n retarding dissolution. Based on these results,... 

So far, the effects of semi-dilute solutions are qualitatively clear. Ambiguity comes in, however, when the overlap concentration has to be defined quantitatively. This ambiguity arises from the fact that the volume of a macromolecule cannot be uniquely defined. Because of the segment mobility the shape of a macromolecule varies in time such that only a statistical description can be made. As... 

The tendency to undergo aggregation in cyclohexane increases with the generation number. It causes strong signal broadening attributable to hindrance of segment mobility. With 5 the effect is so pronounced that a sharply resolved... 

In the case of 3,5 substitution, the excluded volume from the rotation of the disubstituted phenyl is large leading to an increased free volume. The local motions thus becomes easier in the glassy state. On the contrary, the 2,5 substitution, for which the net effect of the steric hindrance, the overall bulkiness of the substituents and absence of dipole-dipole interaction result in a higher segmental mobility, has not an important available free volume in the glassy structure. The... 

Another study was conducted by this group of the effect of polymer microstructure on the segmental mobility. In the first of two papers [32] they compared the rates of 13C Tx relaxation for five samples of BR having varying proportions of 1,2-vinyl, cis-1,4- and trans-1,4 double bonds. The high-resolution solution-state spectra can be resolved into... 

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