Monodisperse molecular weight

High molecular weight monodisperse polystyrene latexes have been prepared by this method [158]. A number of factors were found to influence the size and dispersity of the particles. The size decreased with increasing surfactant concentration and decreasing internal phase volume, and a more monodisperse latex... 

Usually the adjustment of properties is carried out by using mixtures of high molecular weight polydispersed telechelic prepolymers and simple low molecular weight molecules. Recently, we produced a review about the prepolymers mentioned above [8] which we will not describe in this paper. This work concerns the synthesis of low molecular weight monodispersed molecules, their properties and eventually their applications. 

The polymers chosen for the initial stages of our studies were poly-(methyl methacrylate) and polystyrene. There were several reasons for this choice, the most important being (1) well-characterized, low-molecular-weight monodisperse samples of poly(methyl methacrylate) and polystyrene are readily available, or at least relatively easy to synthesize and (2) the poly (methyl methacrylate) /polystyrene system is especially amenable to study by scanning electron microscopy, as we... 

Weinberg RA, Penman S. Small molecular weight monodisperse nuclear RNA. J. Mol. Biol. 1968 38 289-304. 

Fig. 7. a Crazes displacement profiles and b craze surface stress profiles in a commercial polydisperse PS, a monodisperse PS and a blend of a high and a low molecular weight monodisperse PS (5 % M 4000 in 200,000 M J... 

Figure 39 shows the results of this fitting procedure for the data of Yang et al, for different molecular weight monodisperse polystyrenes. Computed fibril stability curves for residence times of 150 sec and 250 sec, as well as 195 sec which produces the best fit, are shown as solid lines. Note that varying the residence time simply appears to scale the fibril stability curve up or down by nearly a constant factor without... 

Characterization of Block Copolymers. The copolymers were characterized by velocity ultracentrifugation, osmotic pressure, and ordinary element analysis in order to determine the molecular weight monodispersity of the copolymers and the degree of contamination with the corresponding homopolymers, the number average molecular weight (Mn), and the fractional compositions of the block copolymers, respectively. 

Calibration of a packed column also presents difficulties when using SEC to characterize EOR polymers. No large molecular weight, monodispersed water-soluble polymer standards are available to relate elution volume to molecular weight. Consequently, the usual SEC calibration methods are not applicable and special calibration techniques must be applied. 

In most cases the different constituent blocks are incompatible, giving rise to intramolecular phase separation, but the chemical connectivity restricts the special dimension of phase segregation to the nanoscale. As a result, at sufficiently high molecular weight, monodisperse block copolymers form a rich variety of self-assembled structures or an array of periodic nanostructures with a periodicity of 10-100 nm, commonly referred to as microphase-separated structures. By changing the relative composition, the compatibility between the component polymers, and the architecture of the copolymer molecules, the size and type of nanostructures can be precisely controlled [1-6]. 

It seems that the ideal Wurtz-type coupling reaction of chlorosilanes combines all recent scientific results, using an optical active solvent at low temperatures and additives that increase the yield of desired polymer. To what extent the combination of these promising synthetic methods is able to deliver a high molecular weight monodisperse polysilane in high yields remains to be determined. 

If there is actually a flat plateau in the curve of either the storage modulus or the compliance, it is easy to obtain the value of the plateau modulus, but except for very high molecular weight, monodisperse, samples this is not the case, and most reported values are estimated from loss modulus data using the following relationship [41, p. 373]. 

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