Polymer Systems in Solution

In this section, Ru(bpy)j+ and its polymer analogoues are mainly described, since the Ru complex is best known as the photocatalyst that can photolyze water theoretically. 

2 -bipyridyl)ruthenium(II) was anchored onto poly(4-vinyIpyridine) (PVP) (6) 28 29), but the polymer complex is not suitable as photocatalyst, because it is susceptible to photoaquation. A polymer complex containing Ru bpy) + pendant groups was first prepared by reaction of polystyrene (PSt) as shown in Eq. (15)30). 

The polymer complex, Ru(PSt-bpy) (bpy)2+, is stable under irradiation, and shows almost the same sensitizing ability in the photoreduction of MV2+ in solution 30,31). The solubility of the polymer complex, quite different from the monomeric Ru(bpy)2+ allows its use as solid phase catalyst in water as described in the next section 31). 

4-Methyl-4 -vinyl-2,2 -bipyridyl (7 Vbpy) was prepared and the Ru complex of its trichlorosilylethyl derivative was coated on n-Sn02 by condensation of the surface hydroxyl groups 32). Anodic photocurrent obtained at the Ru(bpy)2+ bound n-Sn02 semiconductor electrode was about twice than that obtained at the bare Sn02 dipped in 0.1 N H2S04 solution of Ru(bpy)f +.  

Vbpy was copolymerized with styrene to give the copolymer, P(St-Vbpy), which was then treated with cis-Ru(bpy)2Cl2 in xylene/n-butylalcohol = 1/4 (vM under reflux to form polymer pendant Ru(bpy)2+ (8 Ru[P(St-Vbpy)] (bpy)2+)10j. 

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The high effectiveness of the PL method for solving various problems of polymer chemistry and physics is mostly due to the features that distinguish this method from other methods applied to the investigation of the structure and properties of polymers in multicomponent polymer systems in solution. 

Figure 4.23. Schematic representation of "intelligent" polymer systems in solution, on surfaces and as hydrogels [113].

SECTION I Multiphase Polymer Systems in Solution Phase... 

Isothermal titration calorimetry (ITC) has been employed to investigate the thermodynamic parameters associated with the interactions between polymer systems in solution and other solvents [57]. Other studies employing ITC, carried out recently, have examined the interactions between poly(NIPAM) microgels and amino acids [58] as well as SDS [59]. 

While Eq. (9.22) clearly relates A2 to u and M, it vaguely indicates that the value of A2 for a polymer system in solution decreases with the increasing value of M. It is vague because the theory has not specified yet the significance of u. To interpret u, the model needs to be improved. 

DEPT is a very simple and useful sequence for the determination of the proton multiplicity of carbons and is of considerable value for the study of polymer systems in solution and in the solid state [54,55]. 

Even in the absence of flow, a polymer molecule in solution is in a state of continual motion set forth by the thermal energy of the system. Rotation around any single bond of the backbone in a flexible polymer chain will induce a change in conformation. For a polyethylene molecule having (n + 1) methylene groups connected by n C — C links, the total number of available conformations increases as 3°. With the number n encompassing the range of 105 and beyond, the number of accessible conformations becomes enormous and the shape of the polymers can only be usefully described statistically. 

A polymeric structure can be generated by intermolecular coordination of a metalloporphyrin equipped with a suitable ligand. Fleischer (18,90) solved the crystal structure of a zinc porphyrin with one 4-pyridyl group attached at the meso position. In the solid state, a coordination polymer is formed (75, Fig. 30). The authors reported that the open polymer persists in solution, but the association constant of 3 x 104 M 1 is rather high, and it seems more likely, in the light of later work on closed macrocycles (see above), that this system forms a cyclic tetramer at 10-3 M concentrations in solution (71,73). 

The chemical potential of the polymer is affected by "impurities" such as solvents or copolymerized units. For an equilibrium condition in the presence of water as the diluent, the melting temperature of starch (Tm) would be lower because p in the presence of diluent is less than pi). For the starch-water system at equilibrium, the difference between the chemical potentials of the crystalline phase and the phase in the standard state (pure polymer at the same temperature and pressure) must be equal to the decrease in chemical potential of the polymer unit in solution relative to the same standard state (Flory, 1953). By considering the free energy of fusion per repeating unit and volume fraction of water (diluent), the... 

Interest in optically active polymers arose from analogy with macromolecules of biological origin. In addition, there was the hope to obtain new information to clarify the stereochemical features of synthetic polymers this, in fact, did come about. Attempts to direct the course of polymerization using chiral reagents had been made already prior to the discovery of stereospecific polymerization. It was only after the 1950s, however, that the problem of polymer chirality was tackled in a rational way. The topic has been reviewed by several authors (251-257). In this section I shall try to illustrate three distinct aspects the prediction of chirality in macromolecular systems, the problems regarding the synthesis of optically active polymers, and polymer behavior in solution. 

Figure 6 shows the phase diagrams plotting temperature T vs c for PHIC-toluene systems with different Mw or N [64], indicating c( and cA to be insensitive to T, as is generally the case with lyotropic polymer liquid crystal systems. This feature reflects that the phase equilibrium behavior in such systems is mainly governed by the hard-core repulsion of the polymers. The weak temperature dependence in Fig. 6 may be associated with the temperature variation of chain stiffness [64]. We assume in the following theoretical treatment that liquid crystalline polymer chains in solution interact only by hardcore repulsion. The isotropic-liquid crystal phase equilibrium in such a solution is then the balance between S and Sor, as explained in the last part of Sect. 2.2. 

Radioprotection. The processes of crosslinking and degradation observed in polymers irradiated in the pure state can also be observed in polymers irradiated in solution. The presence of a solvent can intervene in the reaction in several ways thus it allows increased polymer mobility, and some of the radiolytic products of the solvent may react with the polymer or with the polymer radicals, etc. The polymer-water system is of particular interest in that it provides a simple model for some radiobiological systems and can be analyzed far more readily. 

Kasapis, S., Morris, E.R., Norton, I.T., Gidley, M.J. (1993b). Phase equilibria and gelation in gelatine/maltodextrin systems. Part II. Polymer incompatibility in solution. Carbohydrate Polymers, 21, 249-259. 

Flory-Huggins /u. The Flory-Huggins n value measures the interaction between polymer and solvent (plasticizer). It derives from the so-called lattice theory, which represents a statistical approach to the behavior of polymer molecules in solution (10, 14, 75, 16, 22). The n value may be experimentally determined for any polvmer-plasticizer system (where the plasticizer can dissolve the polymer) by osmotic pressure measurements according to the relation ... 

Two theoretical approaches for calculating NMR chemical shift of polymers and its application to structural characterization have been described. One is that model molecules such as dimer, trimer, etc., as a local structure of polymer chains, are in the calculation by combining quantum chemistry and statistical mechanics. This approach has been applied to polymer systems in the solution, amorphous and solid states. Another approach is to employ the tight-binding molecular orbital theory to describe the NMR chemical shift and electronic structure of infinite polymer chains with periodic structure. This approach has been applied to polymer systems in the solid state. These approaches have been successfully applied to structural characterization of polymers... 

For liquids of low viscosity, a useful measurement technique is the tensiometer, schematically represented in Fig. 2.56. Here, the surface tension is related to the force it takes to pull a platinum ring from a solution. Surface tension for selected polymers are listed in Table 2.12 [71 ], for some solvents in Table 2.13 [58] and between polymer-polymer systems in Table 2.14 [71],... 

Summary The classical treatment of the physicochemical behavior of polymers is presented in such a way that the chapter will meet the requirements of a beginner in the study of polymeric systems in solution. This chapter is an introduction to the classical conformational and thermodynamic analysis of polymeric solutions where the different theories that describe these behaviors of polymers are analyzed. Owing to the importance of the basic knowledge of the solution properties of polymers, the description of the conformational and thermodynamic behavior of polymers is presented in a classical way. The basic concepts like theta condition, excluded volume, good and poor solvents, critical phenomena, concentration regime, cosolvent effect of polymers in binary solvents, preferential adsorption are analyzed in an intelligible way. The thermodynamic theory of association equilibria which is capable to describe quantitatively the preferential adsorption of polymers by polar binary solvents is also analyzed. 

The mesoscopic approach gives an amazingly consistent picture of the different relaxation phenomena in very concentrated solutions and melts of linear polymers. It is not surprising the developed theory is a sort of phenomenological (mesoscopic) description, which allows one to get a consistent interpretation of experimental data connected with dynamic behaviour of linear macromolecules in both weakly and strongly entangled polymer systems in terms of a few phenomenological (or better, mesoscopic) parameters it does not require any specific hypotheses. 

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