Macromolecular Substance

Humic substances in sediments and soils have commonly been, defined as heteropolycondensates of decomposing plant and animal detritus 46. For lack of a better structural definition, these macromolecular substances have been divided into three categories fulvic acids and humic acid and humin. Fulvic acids and humic acids are soluble in dilute alkaline solutions, whereas humin is insoluble. 

The proteins are a group of macromolecular substances of great importance in biochemistry. Their very name provides testimony to this - it was coined by Mulder in 1838 from the Greek word proteios , meaning of first importance . They appear in all cells, both animal and plant, and are involved in all cell functions. 

Polyelectrolytes are macromolecular substances whose molecules have a large number of groups that are ionized in solution. They are termed macroions or poly ions and are studied most often in aqueous solutions. 

In his x-ray work Mark showed a greater range of interests than the other investigators in the field. Mark and his collaborators studied elements, both metallic and nonmetallic, minerals, inorganic compounds, simple organic compounds, condensed gases, and macromolecular substances, and in addition they studied the physics of x-rays and of the diffraction phenomenon. 

Mark s x-ray work on fibrous macromolecular substances began in 1925, with his publication, together with Katz, of a paper on cellulose. He continued the work on cellulose with Meyer and Susich (1929). In 1926 he and Hauser published a report of their studies of rubber. He had developed excellent ideas about the nature of rubber and the explanation of its extensibility and elasticity. I remember that when I visited him in Ludwigshafen in the summer of 1930 both he and I took... 

Thus, dendrimers exhibit a unique combination of (a) high molecular weights, typical for classical macromolecular substances, (b) molecular shapes, similar to idealized spherical particles and (c) nanoscopic sizes that are larger than those of low molecular weight compounds but smaller than those of typical macromolecules. As such, they provide unique rheological systems that are between typical chain-type polymers and suspensions of spherical particles. Notably, such systems have not been available for rheological study before, nor are there yet analytical theories of dense fluids of spherical particles that are successful in predicting useful numerical results. 

Table 1. Effective Macromolecular Substances Group I (Effective in the presence of Cu(II) ion)...

As already shown, conventional macromolecules (or polymers) consist of a minimum of a several hundred covalently linked atoms and have molar masses clearly above 10 g/mol. The degree of polymerization, P, and the molecular weight, M, are the most important characteristics of macromolecular substances because nearly all properties in solution and in bulk depend on them. The degree of polymerization indicates how many monomer units are linked to form the polymer chain. The molecular weight of a homopolymer is given by Eq. 1.1. 

The properties of solutions of macromolecular substances depend on the solvent, the temperature, and the molecular weight of the chain molecules. Hence, the (average) molecular weight of polymers can be determined by measuring the solution properties such as the viscosity of dilute solutions. However, prior to this, some details have to be known about the solubility of the polymer to be analyzed. When the solubility of a polymer has to be determined, it is important to realize that macromolecules often show behavioral extremes they may be either infinitely soluble in a solvent, completely insoluble, or only swellable to a well-defined extent. Saturated solutions in contact with a nonswollen solid phase, as is normally observed with low-molecular-weight compounds, do not occur in the case of polymeric materials. The suitability of a solvent for a specific polymer, therefore, cannot be quantified in terms of a classic saturated solution. It is much better expressed in terms of the amount of a precipitant that must be added to the polymer solution to initiate precipitation (cloud point). A more exact measure for the quality of a solvent is the second virial coefficient of the osmotic pressure determined for the corresponding solution, or the viscosity numbers in different solvents. 

Chemical constitution, steric configuration and, in some cases, details about chain conformation, aggregation, association, and supramolecular self-organization behavior of macromolecular substances can be determined using high-resolution nuclear magnetic resonance (NMR) spectroscopy. This spectroscopic technique is sensitive towards nuclei with a nuclear spin different from zero. 

The refractive index is an important quantity for characterizing the structure of polymers. This is because it depends sensitively on the chemical composition, on the tacticity, and - for oligomeric samples - also on the molecular weight of a macromolecular substance. The refractive indices (determined using the sodium D line) of many polymers are collected in the literature. In order to characterize a molecule s constitution one requires knowledge of the mole refraction, Rg. For isotropic samples, it can be calculated in good approximation by the Lorentz-Lorenz equation ... 

Amongst the important chemical conversions of macromolecular substances are the various reactions of cellulose. The three hydroxy groups per CRU can be partially or completely esterified or etherified. The number of hydroxy groups acetylated per CRU are indicated by the names, i.e., cellulose triacetate, cellulose 2-acetate, etc. Another commercially important reaction of cellulose is its conversion to dithiocarboxylic acid derivatives (xanthates). Aqueous solutions of the sodium salt are known as viscose they are spun into baths containing mineral acid, thereby regenerating the cellulose in the form of an insoluble fiber known as viscose rayon. 

Likewise, in the preparation of many ion-exchange resins, suitable functional groups are introduced by secondary reactions of macromolecular substances (that are generally crosslinked see Sect. 5.2). In this context the utilization of crosslinked polystyrene resins or poly(acrylamide) gel in the solid-phase synthesis of polypeptides (Merrifield technique) or even oligonucleotides should be mentioned. After complete preparation of the desired products they are cleaved from the crosslinked substrate and can be isolated. 

In chemical reactions between low-molecular-weight compounds, new substances are formed that can, in principle, be separated from the unconverted reactants and by-products, e.g., by means of chromatography. With chemical reactions of macromolecular substances the situation is more complicated in that the main reaction and side reactions take place on the same molecular framework. If, for example, only 80 out of 100 CRUs in a polymer chain react in the desired sense while the rest either does not react at all or reacts in some other way, the remaining 20 units cannot be separated from the others since they all belong to the same macromolecule consequently, one cannot obtain a chemically uniform reaction product. 

While reactions of low-molecular-weight compounds can sometimes be carried out in the gas phase, this technique is not applicable to macromolecular substances since they are not volatile. However, it is indeed possible to let low-molecular reagents act upon solid or dissolved polymers in gaseous form. This is done, for example, in the commercial preparation of methylcellulose by conversion of alkali cellulose with gaseous methyl chloride. 

---