Macromolecular structure molecular weight

This chapter also discusses those factors that play a key role on the segregation process that can be classified as entropic and enthalpic factors. Whereas entropic factors include those related with the macromolecular structure (molecular weight or degree of branching), enthalpic factors involve the chemical functionality of the components in the polymer blend. In addition, the environment of exposure can dramatically modify the segregation depending on the polarity. Exposure of a polymer surface to a moist atmosphere resulted in an interfacial enrichment in the polar component. On the contrary, vacuum or dry environments favor the interfacial segregation of the less polar additive. 

Unfortunately, the potential usefulness of these polymers is not easily assessed. Variations in macromolecular structure, molecular weight, branching, ionic character, and hydrogen-bonding capacity of each pol3mier type will, of course, cause drastic behavioral differences under a given set of field conditions. 

As a polycation, chitosan spontaneously forms macromolecular complexes upon reaction with anionic polyelectrolytes. These complexes are generally water-insoluble and form hydrogels [90,91]. A variety of polyelectrolytes can be obtained by changing the chemical structure of component polymers, such as molecular weight, flexibility, fimctional group structure, charge density, hydrophilicity and hydrophobicity, stereoregularity, and compatibility, as... 

Elharfaoui N., Djabourov M., Babel W.. Molecular weight influence on gelatin gels structure, enthalpy and rheology. Macromolecular Symposia 256 (2007) 149-157. 

Because of their high molecular weight and their defined structure, dendrimers offer themselves for studying the expression of chirality on a macromolecular level. The construction of configurationally uniform macromolecules is otherwise a complex task but can be achieved more easily with dendrimers because of repetitive synthesis from identical (chiral) building blocks. Comparison of optical rotation values and circular dichroism (CD) spectra should demonstrate what influence there is of the chiral building blocks on the structure of the whole dendrimer. 

Different classifications for the chiral CSPs have been described. They are based on the chemical structure of the chiral selectors and on the chiral recognition mechanism involved. In this chapter we will use a classification based mainly on the chemical structure of the selectors. The selectors are classified in three groups (i) CSPs with low-molecular-weight selectors, such as Pirkle type CSPs, ionic and ligand exchange CSPs, (ii) CSPs with macrocyclic selectors, such as CDs, crown-ethers and macrocyclic antibiotics, and (iii) CSPs with macromolecular selectors, such as polysaccharides, synthetic polymers, molecular imprinted polymers and proteins. These different types of CSPs, frequently used for the analysis of chiral pharmaceuticals, are discussed in more detail later. 

Protein polymers based on Lys-25 were prepared by recombinant DNA (rDNA) technology and bacterial protein expression. The main advantage of this approach is the ability to directly produce high molecular weight polypeptides of exact amino acid sequence with high fidelity as required for this investigation. In contrast to conventional polymer synthesis, protein biosynthesis proceeds with near-absolute control of macromolecular architecture, i.e., size, composition, sequence, topology, and stereochemistry. Biosynthetic polyfa-amino acids) can be considered as model uniform polymers and may possess unique structures and, hence, materials properties, as a consequence of their sequence specificity [11]. Protein biosynthesis affords an opportunity to completely specify the primary structure of the polypeptide repeat and analyze the effect of sequence and structural uniformity on the properties of the protein network. 

---