Homopolymers, simple, solubility

The qualitative analysis is quite simple if the homopolymers differ in their solubility, for example, when one homopolymer is soluble in a solvent where the other is not. In this case a sample of the materieil is extracted with that solvent. The reprecipitated extracts and residues are examined for composition. The extraction must, however, be very carefully carried out and repeated several times since polymer mixtures are frequently quite difficult to separate by extraction. If no pure homopolymer is isolated in this way one can be sure that the sample is a genuine copolymer. If the solubility properties of the original homopolymers are insufficiently different it is sometimes possible to induce such differences through chemical transformation, for example, by oxidation and/or hydrolysis. 

Complexity within homopolymers as well as that of PBAs have made the task of analysis and characterization a difficult one. Basically, the task of analysis and characterization of PBAs is not different from that of simple low-molecular weight polymers, provided adequate solubility and sites are available for accepting artificial stimulation responses to those stimuli that may be used as functional tools for characterization. Properties of the blend mainly depend on the homogeneity of blends. The processes that are used for characterization of the PBAs are discussed in the following sections [128-131]. 

Furthermore, in calculations performed manually instead of using software implementing our method, the calculation of the properties of many homopolymers with large repeat units can be simplified by treating them formally as alternating copolymers of smaller repeat units of polymers whose properties have already been calculated. Simple additivity is then assumed to hold for the extensive properties of the alternating copolymer, such as its connectivity indices, cohesive energy, and molar volume. All extensive properties can thus be calculated. Intensive properties, such as the solubility parameter, are defined in terms of extensive properties. Their prediction therefore does not require any detailed calculations either. 

Covenient and versatile as well, the preferred technique at present seems to be copolymerization. Either polymerizable surfactants are copolymerized with small, often polar or hydrophilic, comonomers, creating rather well defined surfactant fragments in the polysoaps [73, 77, 78, 156-168] (Fig. 3e). This strategy is more versatile than exclusive homopolymerization and allows the use of polymerizable surfactants whose homopolymers are not water-soluble, but it still requires considerable synthetic effort. Or, much more facile, simple hydro-phobic monomers are copolymerized with small hydrophilic ones (Fig. 3f), taking full advantage of the choice of commercial or easily accessible monomers [39, 53-55, 153, 169-218]. 

All methods used by organic chemists for the determination of molecular structure are appropriate for the characterization of polymers. However, the simple analysis may not be able to differentiate between a homopolymer, a copolymer, or a blend of polymers. Even with a homopolymer, such as a commercial polypropylene, the solid may contain varying amounts of polymers with different molar masses and stereochemical and block sequence structure. Therefore it is desirable to be able to dissolve the polymer in selective solvents and extract species on the basis of solubility. 

The final product, because of different solubility of homopolymer and copolymer can be separated in fractions of opposite optical rotation by simple solvent extraction. 

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