Synthetic linear macromolecules

Many complex systems have been spread on liquid interfaces for a variety of reasons. We begin this chapter with a discussion of the behavior of synthetic polymers at the liquid-air interface. Most of these systems are linear macromolecules however, rigid-rod polymers and more complex structures are of interest for potential optoelectronic applications. Biological macromolecules are spread at the liquid-vapor interface to fabricate sensors and other biomedical devices. In addition, the study of proteins at the air-water interface yields important information on enzymatic recognition, and membrane protein behavior. We touch on other biological systems, namely, phospholipids and cholesterol monolayers. These systems are so widely and routinely studied these days that they were also mentioned in some detail in Chapter IV. The closely related matter of bilayers and vesicles is also briefly addressed. 

As a general statement it can be concluded that macromolecular conformations different fi om the predominant coil structure are still the exception. Defined spherical secondary-structures have not been obtained by means of noncovalent interactions, since there is no synthetic concept available, distinguishing between inter- and intra-molecular interactions. Formation of globular structures by linear macromolecules is still a privilege of biomolecules where intermolecular interactions are counteracted by well-coordinated intermolecular interactions [50,51]. Synthetic nanospheres can be obtained by the stepwise synthesis of dendrimers [15] or by polymerization of microgels [52] (see below). 

Aldehyde polymers are probably the oldest synthetic polymers [1—8]. Polyoxymethylene the polymer of formaldehyde, was first described by Butlerov in 1859 and the polymer of chloral was first prepared in 1832 by Liebig. This was about one century before the concept of linear macromolecules was developed. Polyformaldehyde and polychloral were isolated because they were stable at room temperature and above. 

This section is constrained to synthetic linear polymers whose molecules consist of repeating monomeric units of one or very few kinds (as opposed to natural polymeric substances). A few examples of adsorption of natural macromolecules (proteins, humic substances) are presented in Table 4.4 (organic compounds). 

The term synthetic polymer refers equally well to linear, saturated macromolecules (i.e., thermoplastics), to unsaturated polymers (i.e., rubbers), or to any substance based on crosslinkable monomers, macromers, or pre-polymers (i.e., thermosets). The focus of this handbook is on blends of thermoplastics made of predominantly saturated, linear macromolecules. 

This group consists of linear macromolecules of natural, semi-synthetic or synthetic nature and of inorganic colloids. A further subdivision is that of non-ionic, anionic and amphoteric substances (Table 23.14). 

Flexible linear macromolecules make up, as mentioned before, the newest class of molecules and are the molecules most important to man. Their number is practically unlimited. For examples, almost all textile fibers are flexible macromolecules, from cotton, silk, wool, hair, and rayon to nylon, polyesters, and aramid. Many structural materials are also flexible macromolecules, such as lumber, compmsites, polyoxyethylene, poly(vinyl chloride), and nylon. Because of the ease of melting, many flexible macromolecules have earned the name plastics, such as polyethylene, polypropylene, polytetra-fluoroethylene, and polyoxides. Many adhesives such as glues, epoxides, poly-(vinyl alcohol), cyanoacrylic polyesters, and ethylene-vinyl alcohol copolymers are based on flexible macromolecules. The unique combination of viscosity and elasticity in the liquid state makes many flexible macromolecules useful as elastomers, of which natural and synthetic robbers and segmented polyurethanes are best known. Class 2 also includes the biolo cal macromolecules carbohydrates, proteins, and DNA. The biological macromolecules alone are practically unlimited in number, as documented by the variety of forms of life. 

The overall objective of this chapter is to review the fundamental issues involved in the transport of macromolecules in hydrophilic media made of synthetic or naturally occurring uncharged polymers with nanometer-scale pore structure when an electric field is applied. The physical and chemical properties and structural features of hydrophilic polymeric materials will be considered first. Although the emphasis will be on classical polymeric gels, discussion of polymeric solutions and nonclassical gels made of, for example, un-cross-linked macromolecular units such as linear polymers and micelles will also be considered in light of recent interest in these materials for a number of applications... 

Abstract This review highlights recent (2000-2004) advances and developments regarding the synthesis of block copolymers with both linear [AB diblocks, ABA and ABC triblocks, ABCD tetrablocks, (AB)n multiblocks etc.] and non-linear structures (star-block, graft, miktoarm star, H-shaped, dendrimer-like and cyclic copolymers). Attention is given only to those synthetic methodologies which lead to well-defined and well-characterized macromolecules. 

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