Synthetics polymers

Polymers are macromolecules built of smaller units called monomers. The process by which they are formed is called polymerization. They may be synthetic (nylon, Teflon, and Plexiglas) or natural (such as the biopolymers starch, cellulose, proteins, DNA, and RNA). Homopolymers are made from a single monomer. Copolymers are made from two or more monomers. Polymers may be linear, branched, or cross-linked, depending on how the monomer units are arranged. These details of structure affect polymers properties. 

Chain-growth, or addition, polymers are made by adding one monomer unit at a time to the growing polymer chain. The reaction requires initiation to produce some sort of reactive intermediate, which may be a free radical, a cation, or an anion. The intermediate adds to the monomer, giving a new intermediate, and the process continues until the chain is terminated in some way. Polystyrene is a typical free-radical chain-growth polymer. 

Step-growth, or condensation, polymers are usually formed in a reaction between two monomers, each of which is at least difunctional. Polyesters, polyamides, polyurethanes, and epoxy resins are typical examples of step-growth polymers. These polymers grow by steps or leaps rather than one monomer unit at a time. 

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Polymers, or macromolecules as they are sometimes called, are large molecules that are built by repetitive linking of many smaller units called monomers. Polymers can be natural or synthetic. 

The most important natural polymers are carbohydrates (starch and cellulose), proteins, and nucleic acids (DNA and RNA). We will study these biopolymers in the last three chapters of this book, in this chapter, we will focus on some of the most 

Classification of Polymers Free-Radical Chain-Growth Polymerization Cationic Chain-Growth Polymerization Anionic Chain-Growth Polymerization Stereoregular Polymers Ziegler-Natta Polymerization A WORD ABOUT... Polyacetylene and Conducting Polymers Diene Polymers Natural and Synthetic Rubber Copolymers 

Step-Growth Polymerization Dacron and Nylon A WORD ABOUT... Degradable Polymers A WORD ABOUT... Aramids, the Latest in Polyamides 

Online homework for this chapter can be assigned in OWL, an online homework assessment tool. 

Synthetic polymers are made by two main processes. The carbon-chain polymers result from the opening of the double bond in the original olefin by addition polymerisation to give new carbon-carbon bonds  

The hetero-chain polymers are mainly made by elimination of water between a carboxylic acid and an alcohol or an amine to give a polyester or a polyamide respectively. These are the condensation polymers  

Similar products can be made without the elimination of water by ring-opening polymerisation of monomeric cyclic monomers, the lactones and lactams. In this case the repeat unit in the polymer is the same as that in the monomer  

The synthetic polymers based on N-acryloyl amino acid-derivatives developed by Blaschke in the 1970 and transferred to silica-bonded phases in the 1980 are especially useful for the separation of 5- and 6-membered N- and O-heterocycles with chiral centers (Review in Kinkel, 1994). Their wide chemical variety has been intensively exploited by Bayer Healthcare for their portfolio of chiral molecules. One example of this approach has been published in a joint work of Merck and Bayer (Schulte, 2002). This work explicitly shows how important it is to screen different intermediates in addition to the final dmg compound. Due to different selectivities and solubilities, the productivity for the preparative separation can be dramatically different. 

New types of synthetic polymeric CSP are those based on tartaramide as the selector (Andersson et al., 1996) and those based on R,R) or (S,S) trans-1,2-diaminocyclohexane (Zhong, 2005). The first one shows its best performance for strongly hydrophobic molecules, when a high alkane content in the mobile phase can be used. The second one has moderate selectivities and resolutions and a comparable loading to the cellulose-based CSP (Barnhart, 2008). It offers the possibility to reverse the elution order by choosing the other enantiomer of the chiral selector. 

For synthetic polymers, dirt content is seldom an issue although there are occasions when the odd piece of the polymerisation plant may appear as an inclusion in a polymer bale. The source of all polymers, and other ingredients, should be assessed on the basis by which the process is controlled and monitored. Incoming batches should be accompanied with test certificates that are routinely checked for conformity to an agreed specification. The latter may be in accord to the supplier s general specification or a special agreement to meet process demands within the user s factory. 

Polymer bales should always be stored away from sunlight, as this is a cause of gel formation in the uncompounded polymer. 

Polychloroprene (PC) rubbers should not be stored for more than three months and when compounded are best used within three weeks. This is due to a slow crosslinking action that produces unacceptable levels of scorch in PC as well as in chlorobutyl and bromobutyl compounds. 

A large number and quantity of polymers are synthesized and used today. They are used for a variety of purposes clothing, wrapping flhn, plastics, bottle for soda and others, water piping, all kinds of small parts for automobiles and other machinery, and CD/DVD. 

An earlier motivation to produce polymers artificially was to produce natural fibers like silk and/or to modify the natural material to desirable fibers. Cotton is a very good fiber, but silk has some appealing characters such as luster and its soft feel upon touch. But silk was much more expensive. People tried to convert cellulose which was much more abundantly available to silk-like fiber. From this effort came the first synthetic fiber, rayon.  

Three British chemists discovered that cellulose could be solubilized when it was treated with sodium hydroxide and carbon disulfide. The product is called cellulose xanthate. The viscous solution was then extruded through a nozzle into an acidic solution, forming Instrons, silk-like fibers. They patented the process and commercialized the prodnct in 1894. This is rayon. It is chemically still cellulose, but its texture is different from that of cotton. It can be produced from not only from cotton, but also from any pulp. 

Almost a century later, scientists at Courtaulds , a rayon manufacturer, chanced to discover that cellulose could be dissolved when heated in a solvent, A/-methyl morpholine oxide. A new fiber (of cellulose) was produced from this solution. Its brand name is Tencel. It has a luxurious look and feel and yet strong to be made into clothes like jeans. 

TABLE 7.2 Properties of common biodegradable polymers used in biomedical applications 

Basically there are two families of polymers synthetic and natural. Polymers formed by abiotic process by laboratory or industrial synthesis form the family of synthetic polymers and the polymers synthesized in biological systems by specific metabolic pathways form the family of natural polymers. 

Synthetic polymers are either polyolefins synthesized from olefin and alkene monomers by covalent bonding or polymers of esters, amides, urethanes, and some other functional group monomers. Polyethylene, polypropylene, polystyrene, polyvinyl chloride, and Teflon are some common examples of polyolefins and polyalkenes. PET, nylon, Kevlar, and Spandex are some examples of polyesters, amides, and urethanes. 

Some common polyolefin and polyalkenes synthetic polymers. 

Examples of few common polyester, amide, and urethane synthetic polymers. 

Although the focus of this book is on the synthetic degradable polymers, in this chapter, we wiU give an overview of the synthetic as well as natural polymers used for various biomedical applications. The subsequent chapters will discuss in detail the synthesis and processing methodologies of the synthetic polymers. 

Synthetic polymers are man-made polymers, and can be degradable or non-degradable. As biomaterials, degradable synthetic polymers are a more viable 

Poly(a-esters) are polymers with hydrolytically liable aliphafic ester bonds in their backbone. They can be easily synthesized via ring opening or condensation polymerization (see Chap. 2 for more details). They are the most commercially available and researched polymers for biomedical applications [4, 5, 9]. 

PGA has excellent mechanical properties and it can be completely resorbed in 6-12 months under physiological conditions to produce glycolic acid as a degradation product. This acidic degradation product has been linked to the strong inflammatory response which is a disadvantage in biomedical applications [5]. 

PLGA based scaffolds have been used for regenerating bone [24], cartilage [25], tendon [26], skin [27], and nervous tissues [28, 29]. 

Many polymers have been studied for their usefulness in producing pharmacologically active complexes with proteins or drugs. Synthetic and natural polymers such as polysaccharides, poly(L-lysine) and other poly(amino acids), poly(vinyl alcohols), polyvinylpyrrolidinones, poly(acrylic acid) derivatives, various polyurethanes, and polyphosphazenes have been coupled to with a diversity of substances to explore their properties (Duncan and Kopecek, 1984 Braatz et al., 1993). Copolymer preparations of two monomers also have been tried (Nathan et al., 1993). 

The following sections discuss the major properties and conjugation chemistries associated with the use of these polymers in modifying or conjugating proteins and other molecules. 

Protein Modification with Activated Polyethylene Glycols 

Unlike the PEG molecules formed from anionic polymerization techniques, there now exist highly discrete forms of the polymer made by controlled addition of small PEG units to create chains of exacting molecular size. These discrete PEGs have a single molecular weight and do not display the polydispersity of the traditional PEG polymers. See Chapter 18 for a complete discussion of discrete PEG-based reagents and their applications. 

The three reactive chlorines on TsT have dramatically different reactivities toward nucleophiles in aqueous solution. The first chlorine is reactive toward hydroxyls as well as primary and secondary amine groups at 4°C and a pH of 9.0 (Abuchowski, 1977a Mumtaz and Bachhawat, 1991). Once the first chlorine is coupled, the second one requires at least room temperature conditions at the same pH to react efficiently. If two chlorines are conjugated to nucleophilic groups, the third is even more difficult to couple, requiring at least 80°C at alkaline 

A wealth of important materials fall under the general category of synthetic polymers. All share a common theme of being made up of sequences of one or more monomer units. 

One after the other, examine the structures of a number of common monomers. What features, if any, do they have in common What relevance is this to the polymerization process  

One after the other, examine the structures of a number of common polymers. For each, draw the repeating unit, and indicate the chain length (number of repeating units in the strand). Note Each end of a polymer strand has been capped by adding extra atoms. Do not count these atoms as repeating units. Also, use the smallest possible repeating unit. 

It is unrealistic to expect that any single conformer of a polymer will adequately represent the overall size and shape of the polymer. The low-energy conformer for each polymer strand shown here is merely meant to allow identification of the polymer in terms of its components. 

MS is also increasingly used in the characterization and analysis of synthetic polymers. Over the years, Alkah -cationization has also been frequently used to enable the MS analysis of intact synthetic oligomers and polymers, e.g., by addition of Li or Na to condensed-phase sample preparation to be analyzed using ionization techniques like FDI, FAB, PDI, and SIMS. More recently, Alkah -cationization is applied in the MALDI-MS and ESI-MS analysis of synthetic polymers. 

Whereas MALDl-MS and ESl-MS primarily involve condensed-phase ion-attachment processes, -phase ion attachment may be important in APCl. A recent paper reviews the use of APCl and the closely related atmospheric-pressure photoionization (APPl) technique in the characterization of syntltetic polymers [294], Next to protonation, the formation of [M+Na]+-ions is important in APCl-MS analysis of synthetic polymers. 

Recently, more similarity has been observed between the two types of macromolecules. For example, synthetic polymers, which are usually considered to be in the form of flexible random coils, can now be synthesized with the Ziegler-Natta catalysts to have stereoregularity. Furthermore, synthetic polymers can be designed to have helices, just like proteins and nucleic acids. As our knowledge of macromolecules increases, the sharp distinction between synthetic polymers and biological polymers becomes more and more arbitrary. 

In 1929, Carothers classified synthetic polymers into two classes according to the method of preparation used condensation polymers and addition polymers. For condensation (or stepwise reaction) polymers, the reaction occurs between two polyfunctional molecules by eliminating a small molecule, for example, water. The following are examples of condensation polymers  

Addition (or chain reaction) polymers are formed in a chain reaction of monomers which have doubles bonds. The following are examples of addition polymers  

Polymers may be classified into two structural categories linear polymers and branched polymers. Linear polymers are in the form 

Two of the most well-known branched polymers are the star-shaped polymer 

A polymer is a large molecule made up of a repeating sequence of smaller units called monomers. Naturally occurring polymers include DNA and also cellulose, which is composed of repeating glucose units (see Sections 11.1 and 11.4). Synthetic polymers, which are made on a large scale in industry, have found a variety of important applications, e.g. adhesives, paints and plastics. 

Polymers can be divided into addition (or chain-growth) polymers, formed on simple addition of monomers, or condensation (or step-growth) polymers, formed on the addition of monomers and elimination of a by-product such as water. 

The huge polymer manufacturing industry is significant to the environment both as a source of environmental pollutants and in the manufacture of materials used to alleviate environmental and waste problems. Synthetic polymers are produced when small molecules called monomers bond together to form a much smaller number of very large molecules. Many natural products are polymers for example, cellulose produced by trees and other plants, and found in wood, paper, and many other materials, is a polymer of the sugar glucose. Synthetic polymers form the basis of many industries, such as rubber, plastics, and textiles manufacture. 

Many of the hazards from the polymer industry arise from the monomers used as raw materials. Many monomers are reactive and flammable, with a tendency to form explosive vapor mixtures with air. All have a certain degree of toxicity vinyl chloride is a known human carcinogen. The combustion of many polymers may result in the evolution of toxic gases, such as hydrogen cyanide (HCN) from polyacrylonitrile or hydrogen chloride (HCl) from polyvinylchloride. Another hazard presented by plastics results from the presence of plasticizers added to provide essential properties such as flexibility. The most widely used plasticizers are phthalates, which are environmentally persistent, resistant to treatment processes, and prone to undergo bioaccumulation. 

Polymers have a number of applications in waste treatment and disposal. Waste disposal landfill liners are made from synthetic polymers, as are the fiber filters that remove particulate pollutants from flue gas in baghouses. Membranes used for 

I I containing a large number, Y I n, monomer units per H Cl molecule 

TTie chapter summary behw is presented in a programmed format to review the main points covered in this chapter. It is used most effectively by fitting in the blanks, referring back to the chcpter as necessary. The correct answers are given at the end of the summary. 

A low-molecular-weight condensation product of hydroxyacetic acid with itself or compounds containing other hydroxy acid, carboxylic acid, or hydroxy-carboxylic acid moieties has been suggested as a fluid loss additive [164]. Production methods of the polymer have been described. The reaction products are ground to 0.1 to 1500 p particle size. The condensation product can be used as a fluid loss material in a hydraulic fracturing process in which the fracturing fluid comprises a hydrolyzable, aqueous gel. The hydroxyacetic acid condensation product hydrolyzes at formation conditions to provide hydroxyacetic acid, which breaks the aqueous gel autocatalytically and eventually provides the restored formation permeability without the need for the separate addition of a gel breaker [315-317,329]. 

A water-soluble polymer of monoallylamine can be used in conjunction with a sulfonated polymer, such as a water-soluble lignosulfonate, condensed naphthalene sulfonate, or sulfonated vinyl aromatic polymer, to minimize fluid loss from the slurry during well cementing operations [1510,1511]. The polymer 

Organophilic polyphenolic materials for oil-based drilling fluids have been described [407], The additives are prepared from a polyphenolic material and one or more phosphatides. The phosphatides are phosphoglycerides obtained from vegetable oils, preferably commercial lecithin. Humic acids, ligno-sulfonic acid, lignins, phenolic condensates, tannins the oxidized, sulfonated, or sulfomethylated derivatives of these polyphenolic materials may serve as polyphenolic materials. 

Tests showed that a fluid loss additive on a base of a sulfonated tannic-phenolic resin is effective for fluid loss control at high temperature and pressure, and it exhibits good resistance to salt and acid [868]. 

In hydraulic cement slurries, fluid loss additives based on sulfonated or sulfomethylated lignins have been described. 

Introduction. Polymerization reactions were considered briefly in connection with the study of olefins, aldehydes and ketones. The object of the present experiment is to make a further study of polsonerization reactions which are finding extensive industrial application. 

Polymerization reactions involve the union of a number of similar molecules to form a single complex molecule. A polymer is any compound, each molecule of which is formed out of a number of molecules which are all alike, and which are called monomers. In many cases polsonerization can be reversed and the poisoner be resolved to the monomer. Many polymerization reactions which are of industrial importance involve in the initial stages condensations, that is, reactions in which elimination of water or other simple molecules takes place. Compounds which polymerize have some type of unsaturation in the molecule. Olefins, unsaturated halides, esters, aldehydes, dicarboxylic acids, anhydrides, amino acids and amides are among the important groups of compounds which are used in industrial polymerization reactions. The commercial products produced by polymerization reactions may be conveniently classified into (a) resinotds, or synthetic resins (b) elastomers, which possess rubber-like properties and (c) fibroids, used as textile fibers. Two types of resinoids are illustrated in this experiment Bakelite, formed from phenol and formaldehyde, and methacrylate resin formed from an unsaturated ester. 

The acrylate resinoids are esters of acrylic and methacrylic acid. Methyl methacrylate, CH2 = C(CH3)COOH3, is a liquid ester which polymerizes to a transparent resin of high tensile strength. The polymerization is brought about by catalysts such as peroxides and heat. The polymerization is assumed to take place by addition to form linear molecules  

Styrene or vinylbenzene, C6H6CH=CH2, polymerizes rapidly to transparent hard resins which are also assumed to have a linear structure. 

The elastomers are chiefly obtained by the polsonerization of olefins and diolefins. The poisoners are assumed to have a linear structure. A similar linear structure is assumed for the polyamides (Nylon), which have structural similarities to proteins. 

Heller and Pugh (1954) used a slight modification of Zsigmondy s gold number experiment to measure the effect that four samples of poly-(oxyethylene) had on the stabUity of a Faraday gold sol when potassium chloride was added. Their results are shown in Table 2.2. Listed therein are the values of the critical concentration of potassium chloride (cJ q), required to induce the red- blue transformation in the gold sol in the presence of the polymer at a given concentration (1 -0 g dm ). This concentration of polymer 

Two important conclusions emerge from the data of Heller and Pugh. First, there is no doubt that poly(oxyethylene) can protect the gold sol from coagulation by electrolyte. Second, the protective action is enhanced by increasing the molecular weight of the polymer. 

FIGURE 6.1 Hermann Staudinger, the father of modem polymer science, holding a model of a polymer. Used with permission of the Deutsches Museum to WUey. 

When a polymer is altered by chemical reaction and the process is not carried to completion, the modified units are not necessarily distributed at random through the macromolecules. The partial conversion of polyVAC to poly(vinyl alcohol) gives a product in which the residual VAC units tend to occur in blocks [82] (see chapter 2). This conclusion was reached from CNMR studies of the materials dissolved in D2O. The methylene carbon resonances were used to determine the mean lengths of sequences of VAC and of vinyl alcohol units. 

McCormick et al. (2003) studied the structure and dynamics of adsorbed water and polymer components in PEM films and the bulk PEC using H MAS NMR spectroscopy. The films (1-5 bilayers) with poly(diallyl dimethylammonium chloride) (PDADMAC) and poly(sodium-4-styrenesulfonate) (PSS) were adsorbed onto colloidal silica particles. Relaxation and line width measurements showed that the adsorbed water is less mobile in the films than in the analogous PEC. This result can be explained by compacting of the adsorption layer at a surface and enhancement of confined space effects for bound water. Relaxation measurements and H double-quantum (DQ) NMR experiments revealed that polymer dynamics in the PEMs was strongly influenced by the layer number and water content (Eigures 5.18 and 5.19). 2D spin 

FIGURE 5.18 Water chemical shift as a function of water content per ion pair for a five bilayer film. (Adapted with permission from McCormick, M., Smith, R.N., Graf, R., Barrett, C.J., Reven, L., and Spiess, H.W., NMR studies of the effect of adsorbed water on polyelectrolyte multilayer films in the solid state, Macromolecules 36, 3616-3625, 2003. Copyright 2003 American Chemical Society.) 

Nuclear Magnetic Resonance Studies of Interfacial Phenomena 

Schonhoff et al. (2007) and Chavez and Schonhoff (2007) discussed different aspects of the hydration and internal properties of PEM formed by layer-by-layer assembly. Reflectivity techniques monitor the water content and swelling behavior, while spin relaxation monitors water mobility. Odd-even effects in dependence on the number of layers were discussed in terms of an influence of the terminating layer. X-ray microscopy and NMR cryoporometry were used to analyze the 

Many amino acids are condensed together in a sequential manner to form a protein or a polypeptide chain. It may be noted that proteins are not simply linear chains as written above. Such a linear representation showing the sequence of amino acid units is known as the primary structure of a protein. A protein possesses complieated secondary, tertiary and quaternary structures. The secondary and tertiary struetures involve intra- and inter molecular hydrogen bonding interactions. The quaternary structure includes ionic interactions as well. The overall result is that proteins have complex three-dimensional structures. 

In the previous review of work in this area, which dealt with progress up to 1978, attention was drawn to the fact that there had been a shift in the emphasis and type of polymer characterization caused by changing needs. This is essentially correct and the situation has not changed significantly in the intervening period. There is, however, still a substantial literature on the application of the more traditional characterization techniques and this section will continue to concentrate on these, leaving the more modern techniques to be dealt with in separate chapters. 

Techniques.—A novel method for the determination of the number average molar mass (M ) is reported by Kronberg and Patterson, based on the observation that polystyrene and poly(ethylene oxide) are soluble in the nematic and isotropic phases of the liquid crystalline iV-(/ -ethoxybe zylidene)/ n-butylanaline. Presence of a polymer depresses the first-order nematic-Tsotropic melting transition, by decreasing the nematic order, and as liquid crystals tend to exhibit large values of the cryoscopic constant, molar masses of up to 10 may be studied with some accuracy. 

Characterization of polyacetylenes has been facilitated by incorporating long flexible side chains thereby making the polymer soluble in common organic solvents and so amenable to GPC analysis.  

Molar mass determination using photon correlation spectroscopy has been proposed by Selser, who applied a method of cummulants to transform Z-averagc diffusion coefficients and eventually extract both A/ and 

Wohlschiess, K. F. Elgert, and H.-J. Cantow, Angew. Makromol. Chem., 1978,74,323. 

Polymeric coagulants, as stated earlier, are invariably highly cationic in nature, in order that they can neutralise the overall negative charge at the solid-liquid interface. They usually have molecular weights in the order of 250,000 up to 1,000,000. There are a number of different chemical types but the most common are based upon quaternised polyamines, polyDADMAC and polyethyleneimine (PEI). 

Organic coagulants are used mainly in low solids environment such as potable water and industrial effluent treatment. They can also be used in combination with high molecular weight flocculants. In particular, the addition of a coagulant improves filtrate and centrate clarities, when the flocculant treatment alone is imable to attain acceptable levels. 

The polyacrylamide range of products dominate the fiocculant market although, other product types are also used in niche applications and these include polyethylene oxide. 

Dyes and pigments can be incorporated into paper in many ways, including impregnation and surface treatments. Solubility is an important concern, as is the mechanism of binding. Other materials that are part of the papermaking process are foam- and slime-control agents, required to prevent problems with the machinery used to manufacture the paper. 

The cellulose fibers in paper are the starting material for regenerated fibers such as rayon and cellulose acetate, which, together, form the historical bridge from biopolymers to completely synthetic fibers. Synthetic rubber was created in Germany in 1917, but from the forensic perspective, a much more important advance was the S5mthesis of nylon (specifically, nylon 6,6) in 1935. The discovery of nylon is credited to Dr. Wallace Carothers, who worked at DuPont Chemical Corp. Initially, his work had been with esters and phenols, but he became interest in amides for possible use in the then-infant world of polymer science. What would become known as nylon was developed in 1935 and commercialized in 1939, initially for women s hosiery. World War n jump-started the polymer indu.stry, and many advances quickly followed. The emphasis here will be on fibers, with later sections in the chapter examining other applications of synthetic polymers. 

In a repeat of a theme seen in many scientific discoveries, one of DuPont Chemical s most femous and profitable polymers was discovered by accident. Teflon, a fluo-ropolymer best known for use in cookware, is highly resistant to most solvents and acids 2ind is used in analytical chemistry in applications such as soil and acid digestion. Teflon was accidentally made for the first time by DuPont chemist Roy Plunkett in 1938. Plunkett had been working with refrigerants based on chlorofluorocarbons when he returned to the lab one momir to find a waxy solid in a container where none should have been. Thus was Teflon bom. 

The free water in a polymer solution freezes by cooling and polymer chains are excluded. 

the local concentration of PVA increases and hydrogen bonding between polymer chains is formed leading to the formation of crystallites. 

Repeated thawing and freezing grow microcrystals and strong 3D networks are formed. 

Generally, the obtained gels are cloudy due to microscopic heterogeneity. However, it is also possible to prepare transparent gels using a mixed solvent of dimethyl sulfoamide and water. 

When polyelectrolytes with differing charges are mixed under appropriate conditions, molecular assemblies via static interactions are formed (Fig. 5(a)) [37], and these will become the crosslink points to form polyelectrolyte complex gels [38]. The characteristics of crosslinking by static bonding are (1) the bond strength is as high as 10-100 kcal/mol (2) it is 

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Proteins often have the same high-affinity isotherms as do synthetic polymers and are also slow to equilibrate, due to many contacts with the surface. Proteins, however, have the additional complication that they can partially or completely unfold at the solid-liquid interface to expose their hydrophobic core units to a hydrophobic surface... 

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. 

Balta-Calleja F J and Vonk G G 1989 X-ray Scattering of Synthetic Polymers (New York Elsevier)... 

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... 

Abstract. This paper presents results from quantum molecular dynamics Simula tions applied to catalytic reactions, focusing on ethylene polymerization by metallocene catalysts. The entire reaction path could be monitored, showing the full molecular dynamics of the reaction. Detailed information on, e.g., the importance of the so-called agostic interaction could be obtained. Also presented are results of static simulations of the Car-Parrinello type, applied to orthorhombic crystalline polyethylene. These simulations for the first time led to a first principles value for the ultimate Young s modulus of a synthetic polymer with demonstrated basis set convergence, taking into account the full three-dimensional structure of the crystal. 

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... 

The biologiccJ function of a protein or peptide is often intimately dependent upon the conformation(s) that the molecule can adopt. In contrast to most synthetic polymers where the individual molecules can adopt very different conformations, a protein usually exists in a single native state. These native states are found rmder conditions typically found in Uving cells (aqueous solvents near neutred pH at 20-40°C). Proteins can be unfolded (or denatured) using high-temperature, acidic or basic pH or certain non-aqueous solvents. However, this unfolding is often reversible cind so proteins can be folded back to their native structure in the laboratory. 

Polymerisation involves the chemical combination of a number of identical or similar molecules to form a complex molecule. The resulting polymer has a high molecular weight. The term synthetic polymer is usually employed to denote these compounds of very high molecular weight. 

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). 

The preparation of synthetic polymers is hardly suitable for the ordinary organic laboratory. However, a few simple demonstration experiments are described below which, it is hoped, will provide an elementary introduction to the subject. 

Chapters V-X deal respectively with Heterocyclic and Alicyclic Compounds Miscellaneous Reactions Organic Reagents in Inorganic and Organic Chemistry Dyestuffs, Indicators and Related Compounds Some Physiologically-Active Compounds and Synthetic Polymers. Many of these preparations are of course intended for advanced students, but a mere perusal of the experimental details of selected preparations by those whose time for experimental work is limited may assist to impress them on the memory. Attention is particularly directed to the chapter... 

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... 

Edman degradation (Section 27 13) Method for determining the N terminal amino acid of a peptide or protein It in volves treating the material with phenyl isothiocyanate (CgH5N=C=S) cleaving with acid and then identifying the phenylthiohydantoin (PTH derivative) produced Elastomer (Section 10 11) A synthetic polymer that possesses elasticity... 

Laser desorption methods are particularly useful for substances of high mass such as natural and synthetic polymers. Glycosides, proteins, large peptides, enzymes, paints, ceramics, bone, and large... 

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. 

Just as it is not necessary for polymer chains to be linear, it is also not necessary for all repeat units to be the same. We have already mentioned molecules like proteins where a wide variety of different repeat units are present. Among synthetic polymers, those in which a single kind of repeat unit are involved are called homopolymers, and those containing more than one kind of repeat unit are copolymers. Note that these definitions are based on the repeat unit, not the monomer. An ordinary polyester is not a copolymer, even though two different monomers, acids and alcohols, are its monomers. By contrast, copolymers result when different monomers bond together in the same way to produce a chain in which each kind of monomer retains its respective substituents in the polymer molecule. The unmodified term copolymer is generally used to designate the case where two different repeat units are involved. Where three kinds of repeat units are present, the system is called a terpolymer where there are more than three, the system is called a multicomponent copolymer. The copolymers we discuss in this book will be primarily two-component molecules. We shall discuss copolymers in Chap. 7, so the present remarks are simply for purposes of orientation. 

In this section we shall consider three types of isomerism which are encountered in polymers. These are positional isomerism, stereo isomerism, and geometrical isomerism. We shall focus attention on synthetic polymers and shall, for the most part, be concerned with these types of isomerism occurring singly, rather than in combination. The synthetic and analytical aspects of stereo isomerism will be considered in Chap. 7. Our present concern is merely to introduce the possibilities of these isomers and some of the vocabulary associated with them. 

Figure 4.10 Crystal structure of polyethylene (a) unit cell shown in relation to chains and (b) view of unit cell perpendicular to the chain axis. [Reprinted from C. W. Bunn, Fibers from Synthetic Polymers, R. Hill (Ed.), Elsevier, Amsterdam, 1953.]...

We have not attempted to indicate the conditions of temperature, catalyst, solvent, and so on, for these various reactions. For this type of information, references that deal specifically with synthetic polymer chemistry should be consulted. In the next few paragraphs we shall comment on the various routes to polyester formation in the order summarized above and followed in Table 5.3. 

In this section we briefly consider the osmotic pressure of polymers which carry an electric charge in solution. These include synthetic polymers with ionizable functional groups such as -NH2 and -COOH, as well as biopolymers such as proteins and nucleic acids. In this discussion we shall restrict our consideration... 

In addition to an array of experimental methods, we also consider a more diverse assortment of polymeric systems than has been true in other chapters. Besides synthetic polymer solutions, we also consider aqueous protein solutions. The former polymers are well represented by the random coil model the latter are approximated by rigid ellipsoids or spheres. For random coils changes in the goodness of the solvent affects coil dimensions. For aqueous proteins the solvent-solute interaction results in various degrees of hydration, which also changes the size of the molecules. Hence the methods we discuss are all potential sources of information about these interactions between polymers and their solvent environments. 

We have emphasized biopolymers in this discussion of the ultracentrifuge and in the discussion of diffusion in the preceding sections, because these two complementary experimental approaches have been most widely applied to this type of polymer. Remember that from the combination of the two phenomena, it is possible to evaluate M, f, and the ratio f/fo. From the latter, various possible combinations of ellipticity and solvation can be deduced. Although these methods can also be applied to synthetic polymers to determine M, they are less widely used, because the following complications are more severe with the synthetic polymers ... 

The factor 1 - p/p2 cannot be too close to zero, nor can the refractive index of the polymer and the solvent be too similar. These additional considerations limit the choice of solvents for a synthetic polymer, while their values are optimal for aqueous protein solutions. 

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. 

Synthetic polymers Synthetic Processes Synthetic pyridine Synthetic rubber... 

Chiral synthetic polymer phases can be classified into three types. In one type, a polymer matrix is formed in the presence of an optically pure compound to moleculady imprint the polymer matrix (Fig. 10) (107,108). Subsequent to the polymerisation, the chiral template is removed, leaving the polymer matrix... 

Another type of synthetic polymer-based chiral stationary phase is formed when chiral catalyst are used to initiate the polymerisation. In the case of poly(methyl methacrylate) polymers, introduced by Okamoto, the chiraUty of the polymer arises from the heUcity of the polymer and not from any inherent chirahty of the individual monomeric subunits (109). Columns of this type (eg, Chiralpak OT) are available from Chiral Technologies, Inc., or J. T. Baker Inc. 

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). 

Polyoxyethylene. Synthetic polymers with a variety of compositionaHy similar chemical stmctures are as follows. Based on polarity, poly(oxymethylene) (1) would be expected to be water soluble. It is a highly crystalline polymer used in engineering plastics, but it is not water-soluble (see... 

Reactions of the Methyl Groups. These reactions include oxidation, polycondensation, and ammoxidation. PX can be oxidized to both terephthahc acid and dimethyl terephthalate, which ate then condensed with ethylene glycol to form polyesters. Oxidation of OX yields phthaUc anhydride, which is used in the production of esters. These ate used as plasticizers for synthetic polymers. MX is oxidized to isophthaUc acid, which is also converted to esters and eventually used in plasticizers and resins (see Phthalic acids and otherbenzenepolycarboxylic acids). 

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