Of individual macromolecules

The final goal of all attempts is a description, and hopefully also a reliable prediction, of the macromolecular properties in bulk and in moderately concentrated solutions. It may be useful to recall that even the polymerization processes are conducted either in the melt or in fairly concentrated solutions. Under such conditions a complex interplay between the structures of the individual macro-molecules with strong mutual interactions takes place. In order to disentangle the complexity it will be helpful to derive at first a precise picture of the structure of individual macromolecules. Their properties can most adequately be studied... 

In the molecular-kinetic theory of molten polymers there is another approach to the problem which does not employ the notion of engagements. It is based on the analysis of dynamics of individual macromolecules in the medium of their like. In this case the real environment of macromolecules is substituted by a certain averaged continuous medium. The major problem of this approach is to determine the character of this me-... 

Diblock copolymers of NIPA and EO showed somewhat different behavior [45]. The copolymers were synthesized using NIPA monomer and PEO-containing macroinitiator. The copolymers aggregated at high temperature with no collapse of individual macromolecules. The essential feature of the polymers in question consisted in the strong sensitivity of the shape of the particles to the polymer concentration and to the molar ratio of EO to NIPA monomer units. At low polymer concentration, the shape of the aggregates was mainly spherical, as indicated by the low Rg/Rh values (Fig. 12). The Rg/Rh ratio is informative of the shape of particles in solution. Anisotropic particles, such as rods and coils, possess high values of the ratio, while for particles of spheroid form, low values of the ratio are observed (for spher-... 

To explain the fact that HSPAN swells in water to form gel sheets or macroparticles rather than disintegrating into a gel dispersion, we initially felt that chemical bonding must take place between individual particles of water-swollen gel as water evaporates. Although we cannot totally eliminate this possibility, the proposal of primary chemical bonding is not necessary to explain the behavior of these films and conglomerates. For example, Voyutskii (19) has reviewed the formation of films from vulcanized rubber latexes and concludes that film formation in these systems is observed because of interdiffusion of ends of individual macromolecules in adjacent latex particles. This diffusion can take place even though individual latex particles are crosslinked, 3-dimensional networks and the continuity of the resulting films, even when... 

It is known [11] that in polymer solutions there is an equilibrium between associated and solitary macromolecules. Dilute solution consists of individual macromolecules, between which there is practically no intermolecular interaction. Increasing the polymer concentration leads to an increase in the size of the aggregates of macromolecules and in their number in unit volume. In concentrated... 

Even though in vitro experiments necessarily remove biomolecules from the cellular environment, the structures and dynamics of individual macromolecules provide insights to their biological functions. For example, structural studies have revealed that the protein hemoglobin is made up of four interacting subunits, two a subunits and two ft subunits. Furthermore, each subunit has two distinct conformational states, called the R state and the T state, and the energy of interaction between two neighboring subunits in different states is different from that of two subunits in the same state. This phenomenon is the structural basis of the observed allosteric... 

Sergei S. Sheiko was born in Moscow, Russia, in 1963. He received his B.A. degree in Physics from the Moscow Physico-Technical Institute in 1986 and his Ph.D. degree in Physical Sciences with Eduard Oleynik from the Institute of Chemical Physics of the Russian Academy of Sciences in 1990. From 1991 to 2000, he was working with Martin Moller at the University of Twente, Netherlands, and later at the University of Ulm, Germany. In 2001, he completed his Habilitation in Macromolecular Chemistry and joined the Department of Chemistry of the University of North Carolina at Chapel Hill. His main research interests include wetting and ordering phenomena in thin polymer films and functional properties of individual macromolecules. 

The visualization of individual macromolecules demonstrates the potential of AFM methodologies to interrogate soft condensed matter at the level of the fundamental constituents. There are many examples of imaging single DNA and related biologically relevant shape-persistent macromolecules [20], but these will be treated in Sect. 3.3. Here we will focus on man-made artificial polymers and macromolecules, including dendrimers. The literature of AFM studies on shape-persistent macromolecules has been reviewed by Sheiko and Moller and the reader is referred to this paper for further reference [21]. 

In some experiments, mixing or demixing occurs on a much longer time scale. Here, where one studies changes in fluorescence intensity (I) over a period of minutes or hours, the relevant distance scale of the experiment is much larger. For demixing of PS-Ant and PVMF (9), the span is larger than the dimensions of individual macromolecules and probably reflects the size of the initially formed phase domains. In sorption experiments of a small molecule Q into a thin film or small particle labelled with F, the span is the film thickness or particle radius (10). 

Blends of atactic poly(methyl methacrylate) with poly(ethylene glycol), PMMA/PEG, were reported miscible [Colby, 1989]. Their rheology, PMMA/PEG = 50/50 and 80/20 at T = 160-210°C, was studied in a dynamic shear field [Booij and Palmen, 1992]. By contrast with homopolymers, the blends did not follow the time-temperature superposition. The deviation was particularly large at low temperatures. The reason for the deviation is most likely based on the different temperamre dependence of the relaxation functions. The authors concluded that in miscible blends, the temperature dependence of the relaxation times of individual macromolecules depends on composition. This leads to different degrees of mutual entanglement and hence the rubber plateau moduli. 

Destruction of macromolecules as a result of chemical interactions with the environment leads to the fracture of polymer materials with the formation of active components. Participation of individual macromolecules in destruction processes is dependent upon the amount of the constituent reactive groups. Introduction of substituents of different compositions into the polymer chain changes their stability in thermal oxidation reactions and in response to chemical reagents and moisture effects. 

The results of the present study indicate that the ESI-MS technique enables determination of the subtle structure of bio-inspired and natural polyesters. Moreover, the distribution of comonomers in the mass selected copolyester macromolecules can be shown by the ESI-MS" fragmentation experiments, thus demonstrating the utility of this technique for the analysis of individual macromolecules including their end groups and composition. 

The hydrodynamic radius is constant over a forty days period and very similar to the limiting value in water (Table II). This would tend to prove that the action of isopropanol is a stabilization of individual macromolecules, associations being hindered. Such a behaviour is also observed in methanol, where the polydispersity is lower than in distilled water. 

Entanglements of flexible polymer chains contribute to non-linear viscoelastic response. Motions hindered by entanglements are a contributor to dielectric and diffusion properties since they constrain chain dynamics. Macromolecular dynamics are theoretically described by the reptation model. Reptation includes fluctuations in chain contour length, entanglement release, tube dilation, and retraction of side chains as the molecules translate using segmental motions, through a theoretical tube. The reptation model shows favourable comparison with experimental data from viscoelastic and dielectric measurements. The model reveals much about chain dynamics, relaxation times and molecular structures of individual macromolecules. 

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