Chemical constitutions and molecular

The parameter g is the ratio of the mean square radii of gyration of branched and linear polymers having the same chemical constitution and molecular weight. From this treatment, it follows that... 

Characterization of HTPBs chemical constitutions and molecular weights... 

G. Eulitz [13] studied the correlation between chemical constitution and tinctorial strength directly on dissolved pigment samples. He was able to exclude physical crystal parameters, such as particle size distribution and degree of dispersion, by achieving molecular dispersion. His analysis demonstrated the following ... 

This subject has been of continuing interest for several reasons. First, the present concepts of the chemical constitution of such important biopolymers as cellulose, amylose, and chitin can be confirmed by their adequate chemical synthesis. Second, synthetic polysaccharides of defined structure can be used to study the action pattern of enzymes, the induction and reaction of antibodies, and the effect of structure on biological activity in the interaction of proteins, nucleic acids, and lipides with polyhydroxylic macromolecules. Third, it is anticipated that synthetic polysaccharides of known structure and molecular size will provide ideal systems for the correlation of chemical and physical properties with chemical constitution and macromolecular conformation. Finally, synthetic polysaccharides and their derivatives should furnish a large variety of potentially useful materials whose properties can be widely varied these substances may find new applications in biology, medicine, and industry. 

Easson, L. H., Stedman, E., Studies on the relationship between chemical constitution and physiological action. V. Molecular dissymmetry and physiological activity. Biochem. J. 1933, 27, 1257-1266. 

The chemist must learn to live in, and to feel at home in, the world of molecules. It is not enough that he knows the chemical constitution and chemical reactions of the materials around him. To be really effective and successful, he must also develop an intimacy with the molecular world. He must fit himself into the molecular scale of things. He must put that first drummed-in chemical fact that molecules are small in the very back of his mind and replace it by a consciousness that molecules are real, intricate, structural arrangements of atoms in space. 

The diversity of solvents makes classification very complex and many different ways of classifying solvents have been used. Broadly, solvents may be classified as aqueous, nonaqueous molecular, nonaqueous ionic, and atomic. The ways in which solvents are classified according to their chemical constitution and then according to their physical properties are briefly discussed below. 

W. Brugel, Introduction to Infrared Spectroscopy, Wiss. Forschungsber. Naiurw. Reihe 62, 1-366, 1954. A review, with 595 references, on the theory of infrared spectra, on apparatus and methods of study, and on the application to determination of molecular structure and chemical constitution, and to qualitative and quantitative analysis. 

The reactive compatibilization of a binary A7B immiscible polymer blend is usually ensured via the use of a chemical reaction during the melt-blending operation. The reaction leads to the formation of block or graft copolymers miscible, or at least sufficiently compatible, with both polymers A and B. Depending on its chemical composition and molecular architecture, the in situ formed copolymer is able to locate at the interface, improves the adhesion between the two phases, and constitutes a stabilizing barrier against coalescence (Fig. 22.8). 

The previous sections of this chapter have been concerned with methods for determination of average molar masses, molar mass distributions and molecular dimensions. In many instances this information is all that is necessary to characterize a homopolymer when its method of preparation is known. However, for certain homopolymers (e.g. polypropylene, polyisoprene) knowledge of molecular microstructure is of crucial importance. Additionally, for a copolymer it is necessary to determine the chemical composition in terms of the mole or weight fractions of the different repeat units present. It is also desirable to determine the distribution of chemical composition amongst the different copolymer molecules which constitute the copolymer (Section 3.17.6), and to determine the sequence distribution of the different repeat units in these molecules. Furthermore, when characterizing a sample of an unknown polymer the first requirement is to identify the repeat unit(s) present. Thus methods for determination of chemical composition and molecular microstructure are of great intportance. 

There are two aspects in the characterization of polymers and their blends (1) chemical constitution, (2) molecular weight (MW) and its distribution (MWD). Identification of the chemical constitution is conducted by the manufacturer and rarely performed by the industrial or academic users. 

Most properties of linear polymers are controlled by two different factors. The chemical constitution of tire monomers detennines tire interaction strengtli between tire chains, tire interactions of tire polymer witli host molecules or witli interfaces. The monomer stmcture also detennines tire possible local confonnations of tire polymer chain. This relationship between the molecular stmcture and any interaction witli surrounding molecules is similar to tliat found for low-molecular-weight compounds. The second important parameter tliat controls polymer properties is tire molecular weight. Contrary to tire situation for low-molecular-weight compounds, it plays a fimdamental role in polymer behaviour. It detennines tire slow-mode dynamics and tire viscosity of polymers in solutions and in tire melt. These properties are of utmost importance in polymer rheology and condition tlieir processability. The mechanical properties, solubility and miscibility of different polymers also depend on tlieir molecular weights. 

A polymer is a macromolecule that is constructed by chemically linking together a sequent of molecular fragments. In simple synthetic polymers such as polyethylene or polystyrer all of the molecular fragments comprise the same basic unit (or monomer). Other poly me contain mixtures of monomers. Proteins, for example, are polypeptide chains in which eac unit is one of the twenty amino acids. Cross-linking between different chains gives rise to j-further variations in the constitution and structure of a polymer. All of these features me affect the overall properties of the molecule, sometimes in a dramatic way. Moreover, or... 

Some substances are odorous, others are not. Humans can smell at a distance if one smells the roses in a garden, it is not ordinarUy considered that part of the rose is in contact with the nose. Substances of different chemical constitution may have similar odors. Substances of similar constitution usuaUy have similar odors, eg, in a homologous series nevertheless, even stereoisomers may have different odors. Substances of high molecular weight are usuaUy inodorous and often nonvolatile and insoluble. The quaUty as weU as the strength of odor may change on dUution. 

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