Naturally occurring monomers

Terpenes, specifically monoterpenes, are naturally occurring monomers that are usually obtained as by-products of the paper and citms industries. Monoterpenes that are typically employed in hydrocarbon resins are shown in Figure 2. Optically active tf-limonene is obtained from various natural oils, particularly citms oils (81). a and P-pinenes are obtained from sulfate turpentine produced in the kraft (sulfate) pulping process. Southeastern U.S. sulfate turpentine contains approximately 60—70 wt % a-pinene and 20—25 wt % P-pinene (see Terpenoids). Dipentene, which is a complex mixture of if,/-Hmonene, a- and P-pheUandrene, a- and y-terpinene, and terpinolene, is also obtained from the processing of sulfate Hquor (82). 

Historically, the first major libraries were oligomers of naturally occurring monomers. A good example would be a library of all possible tripeptides. Using the twenty naturally... 

Precise control of the sequence of amino acid residues Any protein-based polymer sequence utilizing the 20 naturally occurring monomers can be specified using recombinant DNA technology. This allows for equivalent ease of production of diverse protein-based polymer sequences, many of which would otherwise be quite difficult or essentially impossible to prepare due to problems of chemical synthesis and unfavorable energetics in the final polymer. 

In contrast to expensive synthetic fibers, the use of natural fibers is a very cheap means of reinforcement, especially in countries where these natural products are readily available. Natural fibers, when compared to synthetic fibers, have a lower density and a lower tensile modulus. However, a combination of a sisal fiber with a resole type phenolic resin based on cashew nut shell liquid, a naturally occurring monomer, produces a very cost effective composite with a thermal stability greater than 200°C. The cashew nut shell liquid is a mixture of phenol, 3-(8 -pentadecenyl)phenol, 3-(8 -pentadecenyl)-5-(hydroxy)phenol, 3-(8 -pentadecenyl)-5-(hydroxy) -6-methylphenol, and2-(8-pentadecenyl-6-(hydroxy)benzoicacid [195]. 

It is particularly relevant to this chapter and indeed to this book that the very first mention of the synthesis of a macromolecular material should have been through the use of a naturally occurring monomer mixture, namely turpentine. It was in fact Bishop Watson who reported in 1798 that the addition of a drop of sulphuric acid to turpentine produced a sticky resin, but it took another century for chemists to recognize that the properties of this material resembled those of natural rubber [15]. Another half century elapsed before the first systematic studies of the polymerization of terpenes, namely m5Tcene [ 16] and a- and P-pinene [17], were reported. 

Proteins are polymers of naturally occurring monomers called amino acids ... 

Biopolymers are the naturally occurring macromolecular materials that are the components of all living systems. There are three principal categories of biopolymers, each of which is the topic of a separate article in the Eniyclopedia proteins (qv) nucleic acids (qv) and polysaccharides (see Carbohydrates Microbial polysaccharides). Biopolymers are formed through condensation of monomeric units ie, the corresponding monomers are amino acids (qv), nucleotides, and monosaccharides, for proteins, nucleic acids, and polysaccharides, respectively. The term biopolymers is also used to describe synthetic polymers prepared from the same or similar monomer units as are the natural molecules. 

The consensus nucleotide sequence (see Figure 10.20b) used in the crystals is a symmetrized version of naturally occuring API recognition sites, but GCN4 binds to this sequence with a high affinity. Each half-site in this DNA is bound to one monomer of the GCN4 dimer by both sequence-specific and... 

S. Manjula, Studies on Polymerization Characteristics of Naturally Occurring (Renewable) Monomers, Ph.D thesis, Regional Research Laboratory, Trivandrum and Kerala University, Trivandrum, India (1988). 

Finally, the pyrimidine nucleotide 4-thiouridine 5 -triphosphate, also presumably essentially in the syn conformation, cannot serve as a substrate for homopolymerization with E. coli RNA polymerase (54). Small amounts of 4-thiouridine were reported to have been found in naturally occurring transfer RNA from coli (55). Scheit has reported that as a monomer in CDCI3, the base can still pair with adenosine (56). 

Successive 1,4 units in the synthetic polyisoprene chain evidently are preponderantly arranged in head-to-tail sequence, although an appreciable proportion of head-to-head and tail-to-tail junctions appears to be present as well. Apparently the growing radical adds preferentially to one of the two ends of the monomer. Which of the reactions (6) or (7) is the preferred process cannot be decided from these results alone, however. Positive identification of both 1,2 and 3,4 units in the infrared spectrum shows that both addition reactions take place during the polymerization of isoprene. The relative contributions of the alternative addition processes cannot be ascertained from the proportions of these two units, however, inasmuch as the product radicals formed in reactions (6) and (7), may differ markedly in their preference for addition in one or the other of the two resonance forms available to each. We may conclude merely that structural evidence indicates a preference for oriented (i.e., head-to-tail) additions but that the 1,4 units of synthetic polyisoprene are by no means as consistently arranged in head-to-tail sequence as in the naturally occurring poly-isoprenes. 

There are large numbers of naturally occurring representatives, especially of pyrrole that include the important polypyrroles (porphyrins and corrins), and the nitropyrrole antibiotics such as pyr-rolomycins and pyrroxamycin. Derivatives of furan have been used as fungicides and A-vinylpyr-rolidone is an important monomer for the production of blood plasma extenders and for cosmetic applications. On account of the similarity in the pathways for the aerobic degradation of monocyclic furan, thiophene, and pyrrole, all of them are considered here. Anaerobic degradation of furans is discussed in Part 2 of this chapter. 

Substrates coated with alkylphenol-polyethylene oxide-acrylate polymer [607] are useful for demulsifying naturally occurring crude oils. The monomers include oxethylated alkylphenols, such as oxethylated nonylphenol with 6 to 12 ethoxy units, which are esterified with acrylate. 

Polymers are examples of organic compounds. However, the main difference between polymers and other organic compounds is the size of the polymer molecules. The molecular mass of most organic compounds is only a few hundred atomic mass units (for reference, atomic hydrogen has a mass of one atomic mass unit). The molecular masses of polymeric molecules range from thousands to millions of atomic mass units. Synthetic polymers include plastics and synthetic fibers, such as nylon and polyesters. Naturally occurring polymers include proteins, nucleic acids, polysaccharides, and rubber. The large size of a polymer molecule is attained by the repeated attachment of smaller molecules called monomers. 

A naturally occurring lactone, ambrettolide, was polymerized (110) employing the WCl6/(CH3)4Sn catalyst in a molar ratio of monomer/W/ Sn of 50/1/5, affording a high molecular weight unsaturated polyester. 

The development of synthetic materials as substitutes for naturally occurring polymers led to the growth of polymer science. The term "High polymers" is used to represent macromolecules in which more that 100 monomer units are involved. Smaller combinations are referred to as dimer, trimer, tetramer, etc. depending on whether the polymer molecule contains 2, 3, 4...etc. units of monomers. 

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