Synthetic polymer examples

Synthetic Polymers. Examples of polymers in this class include acrylamide—acryHc polymers and their derivatives, polyamines and their derivatives, poly-(ethylene oxide), and allylamine polymers. 

Alternatively the ion exchanger may be a synthetic polymer, for example a sulphonated polystyrene, where the negative charges are carried on the —SO3 ends, and the interlocking structure is built up by cross-linking between the carbon atoms of the chain. The important property of any such solid is that the negative charge is static—a part of the solid—whilst the positive ions can move from their positions. Suppose, for example, that the positive ions are... 

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... 

In practice, synthetic polymers are sometimes divided into two classes, thermosetting and thermo-plMtic. Those polymers which in their original condition will fiow and can be moulded by heat and pressime, but which in their finished or cured state cannot be re softened or moulded are known as thermo setting (examples phenol formaldehyde or urea formaldehyde polymer). Thermoplastic polymers can be resoftened and remoulded by heat (examples ethylene polymers and polymers of acrylic esters). 

Not all synthetic polymers are used as fibers Mylar for example is chemically the same as Dacron but IS prepared in the form of a thin film instead of a fiber Lexan is a polyester which because of its impact resistance is used as a shatterproof substitute for glass It IS a polycarbonate having the structure shown... 

Laser desorption is particularly good for producing ions from analytically difficult materials. For example, lasers can be used with bone, ceramics, high-molecular-mass natural and synthetic polymers, and rock or metal specimens. Generally, few fragment ions are formed. 

Polydisperse polymers do not yield sharp peaks in the detector output as indicated in Fig. 9.14. Instead, broad bands are produced which reflect the polydispersity of synthetic polymers. Assuming that suitable calibration data are available, we can construct molecular weight distributions from this kind of experimental data. An indication of how this is done is provided in the following example. 

Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

The third approaeh to synthetic polymers is of somewhat less commereial importance. There is in fact no universally accepted deseription for the route but the terms rearrangement polymerisation and polyaddition are commonly used. In many respects this process is intermediate between addition and condensation polymerisations. As with the former teehnique there is no moleeule split out but the kinetics are akin to the latter. A typical example is the preparation of polyurethanes by interaction of diols (di-alcohols, glycols) with di-isocyanates Figure 2.7). 

The reinforcing filler usually takes the form of fibres but particles (for example glass spheres) are also used. A wide range of amorphous and crystalline materials can be used as reinforcing fibres. These include glass, carbon, boron, and silica. In recent years, fibres have been produced from synthetic polymers-for example, Kevlar fibres (from aromatic polyamides) and PET fibres. The stress-strain behaviour of some typical fibres is shown in Fig. 3.2. 

Typically RO systems are preceded by pretreatment units to remove suspended solids/colloidal matter and add chemicals that control biological growth and reduce scaling. Membranes are typically made of synthetic polymers coated on a backing (skin). Examples of membrane materials include polyamides, cellulose acetate and sulfonated polysulfone. 

Grafting reactions alter the physical and mechanical properties of the polymer used as a substrate. Grafting differs from normal chemical modification (e.g., functionalization of polymers) in the possibility of tailoring material properties to a specific end use. For example, cellulose derivatization improves various properties of the original cellulose, but these derivatives cannot compete with many of the petrochemically derived synthetic polymers. Thus, in order to provide a better market position for cellulose derivatives, there is little doubt that further chemical modification is required. Accordingly, grafting of vinyl monomers onto cellulose or cellulose derivatives may improve the intrinsic properties of these polymers. 

The simplest synthetic polymers are those that result when an alkene is treated with a small amount of a radical as catalyst. Ethylene, for example, yields polyethylene, an enormous alkane that may have up to 200,000 monomer units incorporated into a gigantic hydrocarbon chain. Approximately 14 million tons per year of polyethylene is manufactured in the United States alone. 

We ve seen on several occasions in previous chapters that a polymer, whether synthetic or biological, is a large molecule built up by repetitive bonding together of many smaller units, or monomers. Polyethylene, for instance, is a synthetic polymer made from ethylene (Section 7.10), nylon is a synthetic polyamide made from a diacid and a diamine (Section 21.9), and proteins are biological polyamides made from amino acids. Note that polymers are often drawn by indicating their repeating unit in parentheses. The repeat unit in polystyrene, for example, comes from the monomer styrene. 

Polymer (Sections 7.10, 21.9, Chapter 31 introduction) A large molecule made up of repeating smaller units. For example, polyethylene is a synthetic polymer made from repeating ethylene units, and DNA is a biopolymer made of repeating deoxyribonucleotide units. 

Of some interest is also co-crosslinking of various synthetic polymers, their blends with natural ones as well as compositions with inert or active fillers numerous patents are devoted to these materials (for example, Refs. [87, 88]). Low doses of crosslinking allow to introduce various physiologically active additives into SAH without any danger of radiation damage. This possibility is particularly attractive for the technology of SAH. 

Two relatively new techniques, matrix assisted laser desorption ionization-lime of flight mass spectrometry (MALDI-TOF) and electrospray ionization (FS1), offer new possibilities for analysis of polymers with molecular weights in the tens of thousands. PS molecular weights as high as 1.5 million have been determined by MALDI-TOF. Recent reviews on the application of these techniques to synthetic polymers include those by Ilantoif54 and Nielen.555 The methods have been much used to provide evidence for initiation and termination mechanisms in various forms of living and controlled radical polymerization.550 Some examples of the application of MALDI-TOF and ESI in end group determination are provided in Table 3.12. The table is not intended to be a comprehensive survey. 

Recovery and reuse of synthetic polymers is by far the most acceptable way of dealing with the problem of waste. Items can rarely be reused as such but instead the polymers from which they are fabricated can be recycled. In principle, polymers can be recycled without any significant loss of their properties. For example, polycarbonate bottles can be recycled into automobile bumpers and then into articles for high performance housing. 

Some of the most hydrophobic synthetic polymers known are polyphosphazenes that bear fluoroalkoxy side groups (1,2,10-12). Examples are shown in structures 11 and 1. ... 

Historically, after the development of oligopeptide-based vesicles, several groups developed and characterized vesicles using polypeptide hybrid systems consisting of polypeptide and synthetic polymer blocks [17-19]. Soon thereafter, vesicles formed entirely from polypeptides, such as poly(L-lysine)-h-poly(L-leucine) and poly(L-lysine)-h-poly(L-glutamate), were developed [20, 21]. This review will focus on recent developments in the formation of vesicles composed of polypeptide hybrid or polypeptide systems, as well as the potential promise of these systems as effective dmg delivery vehicles. A specific example of a polypeptide-based vesicle is shown in Fig. 1, where the hydrophobic segment is a-helical and the hydrophilic segment is a random coil. 

From the viewpoint of synthetic polymer chemistry, although the formation of stereospecific polymers (isotactic and syndiotactic) is very popular, the present polymer is the first example having a double syndiotactic structure. In ad tion, the polymer consists of an alternating zigzag-linear main chain structure. 

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