Polymers, natural

Polymers shown in Table 2.1 are synthetic polymers. However, there are several polymers that also occur naturally. The many known natural polymers include a few famous examples sueh as proteins, deoxyribonucleic acid (DNA), hemoglobin, insulin, starch, natural rubber etc. In order to xmderstand the polymeric nature of these natural substances let us look at proteins and see how they are built from simple monomers. 

Proteins are important naturally occurring polymers that are involved in several biological processes. For example, enzymes catalyze most of the chemical reactions in the biological system. Most of the enzymes are proteins. 

The basic building block (monomer) of all the proteins is an a-amino acid. 

Every protein has a precisely defined a-amino acid sequence. 

An a-amino acid contains an amino group a carboxyl group, a hydrogen atom and a distinctive R group - all of these are bound to an a-carbon atom. Amino acids in solution at neutral pH are in their zwitterionic form i.e., the -NH2 is present in the form of -NHa and the -C(X)H is present in the form of a deprotonated COO. This may be represented in the wedge and Fisher projection forms (Fig. 2.1). 

Some natural potymers and their monomer units. 

Natural Polymers.—The photolysis of tyrosine and its derivatives has been studied in methyl cellulose films. The derivatives were classified as follows according to their photochemical reactions tyrosine and tyramine degraded without the generation of any new, longer-wavelength-absorbing products the 

Macromol. Symp., 28th, 1982, 

Bargon, Proc. lUPAC, Macromol. Symp., 28th, 1982, 297. 

Nenkov, T. Boydantsaliev, A. Steyanov, and V. Kabaivanov, Angcw. Makromol. Chem., 1983, 114, 25. 

Miscellaneoiis Polymers.—Allen et al. have studied the post-cured photo-oxidative stability of di- and tri-acrylate resins having structures (9) or (10) 

Natural Polymers.—Two comprehensive review articles have appeared on wool and cellulose photodegradation. Holt and Milliganhave examined the photo-oxidation of serine, threomine, and cystine side chains in wool. Serine is converted into a-carboxyglycine, cystine to a-formylglycine, and threomine to a-acetylglycine. Waters et have shown that the ph oto- 

Aqueous polysaccharide gels have been investigated by Phillips and co-workers. These workers found that the photochemical processes in gels were the same as in solution suggesting that the gel structure is fluid. 

Nickel and copper ions have been found to inhibit the photodegradation of silk, whereas zinc and chromium ions accelerate the process. Other studies of interest include surface photoreactions on the fibre stalk of wool, e.s.r. studies on polypeptide photolysis, photoyellowing of silk studied by ATR, and the photodiscoloration of wool.  

Miscellaneous Polymers.—Buchanan and McGill have investigated in detail 

Abdd-Bary and E. A. Abdel-Razik, Proc. Ini. Rubber Conf., 1979, 970. 

Branching also occurs in polymers. The branches are extensions of hnked monomer units that protrude from the polymer trunk chain. Branched polymers can also form random coils, but the branches prevent a highly irregular arrangement and, therefore, less crystalhnity results because the molecules cannot line up and pack as well. 

The most easily recognised natural polymer is cellulose, the most abundant organic polymer on earth. It consists of glucose units and is the major component of wood although it is also found in the stems and leaves of many plants. Cotton is a particularly pure form of cellulose. 

Wood-pulp cellulose is the basis of paper manufacture. The process 

Cellulose fibres are crystalline and very strong materials when they are dry. However, they are hydrophilic and in the presence of moisture they absorb water, becoming permeable by microorganisms. For this reason paper became much less important as a food packaging material when the cheap hydrophobic synthetic polymers emerged in the second half of the 20th century. 

Mention has already been made of two polymers that can be obtained naturally from living animals silk (from the silkworm) and wool (from sheep). They are proteins made of various amino acids both are used in textiles. Other biologically derived polymers are also familiar such as wood, starch, and some sugars. We will not cover these in detail here. However, certain cellulosics we will discuss briefly since they are compared to synthetic fibers later. Cellulose is the primary substance of which the walls of vegetable cells are constructed and is largely composed of glucose residues. It may be obtained from wood or derived in very high purity from cotton fibers, which are about 92% pure cellulose. 

The important fiber rayon is simply regenerated cellulose from wood pulp that is in a form more easily spun into fibers. Cellophane film is regenerated cellulose made into film. One method of regeneration is formation of xanthate groups from selected hydroxy groups of cellulose, followed by hydrolysis back to hydroxy groups. 

Cellulose acetate and triacetate may be used as plastics or spun into fibers for textiles. They are made by the reaction of cellulose with acetic anhydride. 

Finally, one last type of natural polymer is natural rubber, obtained from the rubber tree and having the all cw-l,4-polyisoprene structure. This structure has been duplicated in the laboratory and is called synthetic rubber, made with the use of Ziegler-Natta catalysis. 

The biosynthesis of synthetic natural rubber has been completely determined and appears in Fig. 15.1. Many plants and animals use this same biosynthetic pathway to make hundreds of terpenes and steroids from their common isoprenoid building blocks. 

Natural mbber, the other natural hydrocarbon polymer, consisting mainly of cfr-l,4-polyisoprene is relatively resistant to microbial attack in comparison to other natural polymers. A number of micro-organisms have been reported to degrade natural rubber. An enzyme which degrades the mbber was isolated from the extracellular culture medium of Xanthomonas sp., and the erude fractions which are capable of depolymerizing natural mbber in the latex state have been reported.The same authors reported on a Nocardia strain that used natural mbber as its sole carbon source. 

The mechanical synthesis of block and graft copolymers by vibromilling a polymer-monomer blend has been performed by many researchers. Natural polymers (14,17) vinyl polymers (18—27), and heterochain polymers (18, 28-34) have been formed during polymer mechanochemical degradation. Importantly, Simionescu, Vasiliu-Oprea and Neguleanu studied the possibility of carrying out mechanically-induced polycondensations starting from polyesters and diamines (33,35-37). 

Monomers may be in the solid, liquid or gaseous state. In the first phase, blending and comminution is generally carried out to reduce inhomogeneities. For the same reason, polymer particle size can also influence the reaction. For example, in the grafting of vinyl chloride on polycaprolactam, the Cl content of the resultant polymer was 3.71 % and 2.16% when 0.05-0.09 mm and 0.4-0.63 mm diameter polycaprolactam particles were employed (31). To obtain polymer in the desired powder form, the polymer was pulverized and selectively precipitated. 

Many reactions have been performed in the presence of a solvent. However, the solvent must be chosen carefully to avoid reaction with polymer. For example, the low yield for grafts of acrylonitrile on polyamides in the presence of methanol has been shown to be due to the methanolysis (18,31). Generally speaking, the grafted products are principally obtained however minor amounts and homopolymers can also result. The homopolymerization proceeds by an intramolecular transfer reaction between macroradicals and monomers. The amount of homopolymer depends on the system. Details on systems already investigated will be described in the next section. 

Mechanical syntheses are, of course, generally affected by the presence of radical acceptors (20,29). The yield on copolymers also increases with duration of mechanical stress. However, if the milling time is too long, the properties of the graft or block copolymers can be deteriorated by degradation of initial product. The nature of the balls and mill material can also influence the reaction (37) the mechanical activation of inorganic materials. The production of graft and block copolymers on freshly formed surfaces has been established in the lierature. 

Deters (14) grafted acrylonitrile, methyl methacrylate and vinyl chloride on cellulose and cellulose triacetate. The first two monomers were put in the reactor as liquids, the last as a gas. The results are summarized on Table 1. Vinyl chloride did not graft to cellulose (14). 

Polymer Monomer Product fraction Type % Content of respectively N, acetic acid, ora% Graft polymer % 

The photodegradation of wool for upholstery fabrics in cars has been 404 

365 to 254 nm and may be associated with the screening of light by the amide functional groups. Rewinding agents based on nonionic surfactants and sodium phosphates inhibit the photoyellowing of 

Different reaction pathways of the carbonyl - sensitized photo-oxidation of a lignin model compound (AH) in air - saturated dimethoxyethane 

Different modes of reaction for the hydroxyl radical in the model system 

Different reaction channels for ground state oxygen in the model system 

Wool photodiscolouration is also a problem and is normally associated with the photoproducts of tryptophan. These have been identified as N-formyl-kynurenine, k]murenine, tryptamine and oxyindolylalanine. Short wavelength blue light has been found to effectively photobleach the yellowing of wool. These processes have been discussed in detail.  

NMR can be employed effectively for examination of many modification processes for cellulose. Studies on acetylation have been reviewed by Usmanov [101]. The quantitative analysis of NMR data relies upon information derived from specifically modified model analogues. Similarly, C chemical shift data for various cellulose oligomers permit the analysis of the spectra of samples of cellulose acetate. Quantitative analyses for the distribution of acetate groups in cellulose acetates of various types have been achieved. 

The sequence of amino acids in a protein is defined by genes and encoded in the genetic code. Although this genetic code specifies the 20 different amino acids, the residues in a protein are often chemically altered in post-translational modification, either before the protein can function in the cell or as part of control mechanisms. Proteins associate to form complexes that are stable. They can work in concert in order to achieve a particular function. They participate in every function of the cell. Many proteins are enzymes that catalyze biochemical reactions. They are vital to metabolism. The cell shape is maintained by a system of scaffolding. Proteins in 

During the formation of the polypeptide polymeric chain, one water molecule is lost per amino acid. This is why the constituents of the proteins are called amino acid residues. There are four different types of protein structures recognized in the field. These are described in the subsequent text. 

Polypyrrole (4.123), a semiconducting polymer, is rather stable towards UV irradiation, which can even increase its conductivity. However, the stabiUty of polypyrroles against UV irradiation depends on the type of dopant present in the polymer [1520]. Tetrafluoroborate doped polypyrrole (4.124), when exposed to UV radiation, shows a rapid deterioration of electrical conductivity, with a conductivity loss ratio of 0.62 after exposure for 90 h. During the irradiation, polypyrrole tetrafluoroborate undergoes a dedoping reaction, whereby tetrafluoroborate ions decompose to fluoride ions and volatile boron trifluoride gas. 

Polypyrroles doped with perchlorate or with p-toluenesulphonate show high resistance to exposure to UV radiation for up to 90 h. 

This mode of classification is equivalent to die classification based on a correlation time that is extremely sensitive to the change in spin relaxation time as shown in Fig. 1. 

From the relaxation parameters such as C spin-lattice relaxation time (Ti) and H spin-lattice relaxation time in the rotating frame, information on the molecular chain mobility in the various regions of network structures can be obtained (see Table 1 and Fig. 1). 

Accordingly, the gel networks of linear Curdlan consist mainly of molecular chains with a single helix structure. The triple helix content is at most 10%. The crosslink structure is formed by association of these triple and single helices. On the other hand, the main structure of the branched glucan is a triple helix and the partial association of these chains functions as a crosslink structure. Thus, the model based on x-ray diffraction data of the thermally treated Curdlan, stating that the crosslink structure consists of a triple helix, is incorrect. This is why NMR data capable of providing information on structure in situ is desired. To be described, the dynamics data from nuclear magnetic relaxation time measurement can also provide information on the differences in these network structures. 

Agarose gel, which exhibits elasticity similar to that of Curdlan, clearly provides signals from the solution-like region as shown in the upper C DD-MAS spectrum of Fig. 6 [130]. However, a spectrum similar to this can also be obtained by the CP-MAS technique as shown in the bottom spectrum of Fig. 6 (the solid-like region). However, there appears to be a difference in the 77-78.5 ppm resonance, which is the characteristic region of polysaccharide chains. Unlike in the solid-like region, this difference is thought to arise from the random coil structure in 

From the chemical shift and relaxation time measurements in these two spectra, information on local conformation can be obtained. Dynamics also can be determined based on the discussion in the next section. The formation of jS-sheet structure in an amyloid protein is confirmed from not only the preceding empirical chemical shift data accumulation but also from the nonempirical interatomic distance determination [148, 149]. 

Hydrolysis to L-lactic acid and thermal degradation (depolymerisation) to the cyclic dimer L-lactide (LLA) is the general procedure for PLLA recycling [a.246]. For depolymerisation. 

Dextran is a homopolymer of 1,6-linked a-D-glucopyranose monomers (Fig. 5-2 D). The individual polymer chains do not associate on the molecular level to give an ordered three-dimensional structure. It therefore lacks the structural rigidity required for a chromatographic support. To improve the mechanical strength the individual polymer chains are cross-linked, for example, using epichlorohydrin in the case of 

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Gutta percha is a natural polymer of isoprene (3-methyl-l,3-butadiene) in which the configuration around each double bond is trans. It is hard and horny and has the following formula ... 

As examples of natural polymers, we consider polysaccharides, proteins, and nucleic acids. Another important natural polymer, polyisoprene, will be considered in Sec. 1.6. 

The main raw material required for the production of viscose is ceUulose (qv), a natural polymer of D-glucose (Fig. 1). The repeating monomer unit is a pair of anhydroglucose units (AGU). CeUulose and starch (qv) are identical but for the way in which the ring oxygen atoms alternate from side to side of the polymer chain (beta linkages) in ceUulose, but remain on the same side (alpha linkages) in starch. 

Rayon is unique among the mass produced man-made fibers because it is the only one to use a natural polymer (cellulose) directly. Polyesters, nylons, polyolefins, and acryflcs all come indirectly from vegetation they come from the polymerization of monomers obtained from reserves of fossil fuels, which in turn were formed by the incomplete biodegradation of vegetation that grew millions of years ago. The extraction of these nonrenewable reserves and the resulting return to the atmosphere of the carbon dioxide from which they were made is one of the most important environmental issues of current times. CeUulosic fibers therefore have much to recommend them provided that the processes used to make them have minimal environmental impact. 

The polymer market ia the United States is dominated by synthetics with natural polymers constituting about one-eighth ia monetary terms (88). Of the synthetic polymers, most are based on acrylamide. A Hst of producers is as follows producers ia the left-hand column also produce polyamines and p oly qu atemarie s. 

The biosynthesis process, which consists essentially of radical coupling reactions, sometimes followed by the addition of water, of primary, secondary, and phenohc hydroxyl groups to quinonemethide intermediates, leads to the formation of a three-dimensional polymer which lacks the regular and ordered repeating units found in other natural polymers such as cellulose and proteins. 

The present invention provides a wheel cover which improves the aerodynamic properties of the hub-rim-spoke wheels. The wheel cover of the present invention is preferably made of a light weight synthetic or natural polymer, fabric or paper film which is adhesively applied to a wheel through simple manual application. In turn, the aerodynamic wheel cover of the present invention may also be easily removed and replaced to allow on-road repairs of spoke, hub, or rim. 

Biodegradable polymers and plastics are readily divided into three broad classifications (/) natural, (2) synthetic, and (J) modified natural. These classes may be further subdivided for ease of discussion, as follows (/) natural polymers (2) synthetic polymers may have carbon chain backbones or heteroatom chain backbones and (J) modified natural may be blends and grafts or involve chemical modifications, oxidation, esterification, etc. 

The first synthetic polyglycoHc acid suture was introduced in 1970 with great success (21). This is because synthetic polymers are preferable to natural polymers since greater control over uniformity and mechanical properties are obtainable. The foreign body response to synthetic polymer absorption generally is quite predictable whereas catgut absorption is variable and usually produces a more intense inflammatory reaction (22). This greater tissue compatibihty is cmcial when the implant must serve as an inert, mechanical device prior to bioresorption. 

High Peformance Natural Polymers, Leaflet by Asiatic Development Berhad, Wisma Genting, J alan Sultan Ismail, Kuala Lumpui, 1993. 

Manufactured fibers produced from natural organic polymers are either regenerated or derivative. A regenerated fiber is one which is formed when a natural polymer or its chemical derivative is dissolved and extmded as a continuous filament, and the chemical nature of the natural polymer is either retained or regenerated after the fiber-formation process. A derivative fiber is one which is formed when a chemical derivative of the natural polymer is prepared, dissolved, and extmded as a continuous filament, and the chemical nature of the derivative is retained after the fiber-formation process. 

INFLUENCE OE SYNTHETIC AND NATURAL POLYMERS ON ANALYTICAL PROPERTIES OE AZODYES... 

Last years the polymeric surface - active substances began to use as modifiers of organic reagent properties. In our work the behavior of synthetic polymers (polysulphonilpiperidinilmethylenhydroxide (PSPMH), polyvinylpyrrolidone (PVP), polyamines - polyguanidine and metacide) and natural polymers (starch, gelatin) for various molecular masses are investigated. 

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