Polystyrene coil conformation

The two examples of adsorbed side chain substituted macromolecules, i.e., the poly(n-butyl acrylate) brush and the tris(p-undecyloxybenzyloxo) benzoate jacketed polystyrene, demonstrate two rather complementary aspects of the interaction of such molecules with a planar surface. In the first case the two-dimension to three-dimension transition results in a cooperative collapse of an extended coil conformation to a globule. The second case shows a rather high degree ordering with a distinct orientation of the backbone in the substrate plane. Combination of both effects and partial desorption can lead to a repta-tion-hke directed motion as depicted schematically in Fig. 36. 

Figure 4. Experimental verification of Equation 20 for polystyrene in methyl ethyl ketone. Polystyrene is in the random-coil conformation (31).

For flexible synthetic polymers, the chain conformation is commonly controlled by the degree of polymerization (DP), with low-DP polymers having a rather extended chain conformation and high-DP polymers adopting random coil conformations in solution. Recently, Percec, Moller et al. reported extensive studies concerning the chain conformation and supramolecular structure of dendron-substituted polystyrene and polymethacrylate [23], Remarkably, at low DP... 

For nonpolar linear polymers that form coils, Hershey and Zakin observed 40% less DR for polyisobutylene in benzene, a poor solvent, than in cyclohexane, a good solvent.Hunston and Zakin showed that polystyrene in the good solvents, toluene or benzene, gave more DR than the same samples in a poor, mixed solvent of toluene and / 6>-octane as shown in Figs. 1 and These results and those of White and Gordon showed that expanded coil conformations. 

In most cases PAEs have been characterized by either light scattering or GPC with polystyrene as standard. The values obtained by GPC experience the same systematic error, i.e., overestimation of the molecular weight as discussed for the PPEs. However, PAEs, which deviate from linearity, display a more coiled conformation in solution, and a better match of the real molecular weights with the ones obtained by GPC is expected. 

The outstanding ability of hypercrosslinked polystyrene networks to increase several times their volume on contacting the dry polymer with non-solvents is a logical consequence of the main principle of network formation. The polymers have been obtained through the fixation of favorable unstressed chain conformations of the initially highly solvated polystyrene coils, by introducing numerous rigid crossHnks between them. 

The disagreement between the values 3.12 and 2.27 points to the fact that Equation 45 is incorrect owing to the neglect of the concentration dependence of the interaction parameter. The chief result of Vrij (1974) is in the fact that near the spinodal maximum, macromolecules have the statistical coil conformation with sizes slightly different from those in the 0 state at c —> 0 (at Iceist, for the polystyrene-t-cyclohexane system). Generally, however, this may not be the case (Vrij and van den Esker, 1972). 

The lamellar structure consists of plane,parallel, equidistant sheets each elementary sheet of thickness d results from the superposition of two layers one of thickness d formed by the polyvinyl blocks (polybutadiene or polystyrene) in a more or less random coil conformation the other, of thickness dg formed by the polypeptide chains (polybenzylglutamate or polycarbobenzoxylysine) in an a helix conformation, perpendicular to the interface, assembled in a bidi-mensional hexagonal array and generally folded (Fig. 1). 

The same types of polyrotaxanes were also prepared by a different method, Method 2 (Figure 6). In this method, a preformed polymer is used and the cyclic is threaded onto the polymer in a melt or in solution. A solution of 28 and polystyrene in THF under reflux afforded a polyrotaxane with an min value of 5.0X1CT4, much lower than those via Method 1 [69]. Threading 28 on to poly (butylene sebacate) afforded poly(ester rotaxane) 33 of Type 4 [70]. Although a laige excess of cyclic was used, 33 only had a min value of 0.0017. This value is 100-fold lower than that for the corresponding polyrotaxane prepared by Method 1 [19]. A possible reason is that the concentration of chain ends is very low and the random coiled-chain conformation of a polymer disfavors threading. 

Garvey et al.85) made a similar sedimentation study on poly(vinyl alcohol) adsorbed on polystyrene latex particles. Adsorbance of the polymer was also measured. Both the thickness of the adsorbed layer and the adsorbance increased linearly with the square root of the molecular weight. The volume occupied by a polymer molecule in the adsorbed layer was approximately equal to that of the effective hydrodynamic sphere in bulk solution. However, the measured values of LH were greater than the hydrodynamic diameters of the polymer coils in solution. Thus, it may be concluded that adsorbed poly(vinyl alcohol) assumes a conformation elongated in the direction normal to the surface. 

We further assume that the blocks in the aggregates as well as in the continuous phase would have the lowest possible free energy if their coil dimensions would equal those of the corresponding homopolymers in athermic solutions. Conformation restrictions (8, 15, 16, 72), which are caused by a block end being connected with a second block that does not mix with the first one, are thus neglected. (At least one end of each block is situated in the interface.) For blocks of polystyrene and polybutadiene the following equations are valid (19, 24, 33, 56, 65) (with the end-to-end distance h = hi2) ... 

The system described in this investigation is polystyrene-14C adsorbed on Graphon carbon black (graphitized Spheron 6) from six solvents comprising a wide spectrum from good to poor solvent power. Well-characterized materials were selected to elucidate the conformation of polymer molecules at the solid/liquid interface. So far two models have been postulated to describe the conformation of the adsorbed polymer molecules at the solid/liquid interface (9, 13, 14, 18, 19, 21, 27). In the first model the polymer assumes a loop or coil structure in which only a fraction of the polymer segments are attached directly at the interface, and in the second model the polymer forms a relatively flat and compressed interfacial layer with many segments attached to the solid substrate. 

Based on properties in solution such as intrinsic viscosity and sedimentation and diffusion rates, conclusions can be drawn concerning the polymer configuration. Like most of the synthetic polymers, such as polystyrene, cellulose in solution belongs to a group of linear, randomly coiling polymers. This means that the molecules have no preferred structure in solution in contrast to amylose and some protein molecules which can adopt helical conformations. Cellulose differs distinctly from synthetic polymers and from lignin in some of its polymer properties. Typical of its solutions are the comparatively high viscosities and low sedimentation and diffusion coefficients (Tables 3-2 and 3-3). 

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