Cooperative effects, polymer chain conformation

The jump diffusion model with damped vibrations was applied to the analysis of the dynamic scattering laws S(Q,co) of the E-process far above the glass transition temperature Tg, where the conformational transitions are mainly dominated by the intramolecular interactions in a polymer chain, so that it is not necessary to take into accounts intermolecular cooperativity effects on the conformational transitions. 

While thin polymer films may be very smooth and homogeneous, the chain conformation may be largely distorted due to the influence of the interfaces. Since the size of the polymer molecules is comparable to the film thickness those effects may play a significant role with ultra-thin polymer films. Several recent theoretical treatments are available [136-144,127,128] based on Monte Carlo [137-141,127, 128], molecular dynamics [142], variable density [143], cooperative motion [144], and bond fluctuation [136] model calculations. The distortion of the chain conformation near the interface, the segment orientation distribution, end distribution etc. are calculated as a function of film thickness and distance from the surface. In the limit of two-dimensional systems chains segregate and specific power laws are predicted [136, 137]. In 2D-blends of polymers a particular microdomain morphology may be expected [139]. Experiments on polymers in this area are presently, however, not available on a molecular level. Indications of order on an... 

There have been several attempts to relate Kg to the critical molecular weight (Mcr, which is discussed in Chapter 13) based on considerations of the effects of polymer chain entanglements on the large-scale cooperative motions of chain segments involved in the glass transition for example, see references [97-99]. It was also suggested [100,101], from considerations of chain stiffness and the statistics of chain conformations, that Kg should be proportional to a power of... 

Indeed, the existence of purely conformational optical activity is not a unique macromolecular requisite, being well known in low molecular weight atro-pisomerism. However, in polymers it assumes a very specific characteristic connected with the occurrence of cooperative effects which allow transmittance of molecular asymmetry along the chain to very long distances [3]. 

In polymer chains the situation is much more complicated than that described above for butane. The generation of conformational structures depends not only on the rotational barriers due to neighboring groups, but also on the cooperative effects of additional bonds. Also the sense of rotation must be respected, because the two g forms, g" " and g of Fig. 1, are no longer equivalent. 

The photoinduced nanoscale changes at the molecular level induced by light (photoisomerization of the photochromic molecule) are amplified by the cooperative effect of the liquid crystal molecules with the conformation of the polymer chain. The macroscopic movement of these materials, which is characteristic for crosslinked liquid crystalline polymers, strongly correlates with the mesogen alignment. Since such polymer materials can be molded into a variety of shapes and sizes, it is possible to drive components remotely and without direct contact. No wires, electrodes, motors, or gears are necessary. Possible applications are micro actuators and microfiuidic devices. 

An alternative approach, which does not seem to have been explored so far, would involve the construction of a polymer (or micelle) with side chains in which two groups which can cooperate in bifunctional catalysis are attached to a conformationally rigid structure. This approach is clearly much more difficult from the point of view of organic synthesis and systems obtained in this way would still have relatively little resemblance to enzymes. However, if a substrate can be drawn efficiently into a small fraction of the available space in which the local concentration of a bifunctional catalyst is very high, the kinetic effects obtained may justify the required effort in synthesis. 

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