synthetic polymers
(noun)
human-made polymers
Examples of synthetic polymers in the following topics:
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Types of Synthetic Organic Polymers
- Synthetic organic polymers are human-made polymers with various main chain and side chain compositions.
- Synthetic polymers are human-made polymers.
- Poly acrylates are the backbones of common synthetic polymers such as polythene and polystyrene.
- The common PET bottles are made of a synthetic polymer, polyethylene terephthalate.
- Low Density Polyethylene (LDPE) polymers are among the most common types of synthetic organic polymers, which are often found in households.
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Condensation Polymers
- The polyester Dacron and the polyamide Nylon 66, shown in the first diagram, are two examples of synthetic condensation polymers, also known as step-growth polymers.
- In contrast to chain-growth polymers, most of which grow by carbon-carbon bond formation, step-growth polymers generally grow by carbon-heteroatom bond formation (C-O & C-N in Dacron & Nylon respectively).
- Although polymers of this kind might be considered to be alternating copolymers, the repeating monomeric unit is usually defined as a combined moiety.
- Examples of naturally occurring condensation polymers are cellulose, the polypeptide chains of proteins, and poly(β-hydroxybutyric acid), a polyester synthesized in large quantity by certain soil and water bacteria.
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Characteristics of Condensation Polymers
- Condensation polymers form more slowly than addition polymers, often requiring heat, and they are generally lower in molecular weight.
- The following examples of condensation polymers are illustrative.
- Nevertheless, the polymer clearly forms by a step-growth process.
- Many polymers, both addition and condensation, are used as fibers the chief methods of spinning synthetic polymers into fibers are from melts or viscous solutions.
- This cold-drawing treatment may also be used to treat polymer films (e.g.
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Writing Formulas for Polymeric Macromolecules
- The repeating structural unit of most simple polymers not only reflects the monomer(s) from which the polymers are constructed, but also provides a concise means for drawing structures to represent these macromolecules.
- This polymer is called polyethylene rather than polymethylene, (-CH2-)n, because ethylene is a stable compound (methylene is not), and it also serves as the synthetic precursor of the polymer.
- The synthetic methods used to prepare this and other polymers will be described later in this chapter.
- Because of this, polymer molecular weights are usually given as averages.
- Polymers formed by a straightforward linking together of monomer units, with no loss or gain of material, are called addition polymers or chain-growth polymers.
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Condensation Reactions
- Condensation polymers often require heat, form slower than do addition polymers, and are lower in molecular weight.
- This type of reaction is used as a basis for making many important polymers, such as nylon, polyester, and various epoxies.
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Thermosetting vs. Thermoplastic Polymers
- Most of the polymers described above are classified as thermoplastic.
- Such polymers are usually prepared in molds that yield the desired object.
- Because these polymers, once formed, cannot be reshaped by heating, they are called thermosets.
- The initial display is of Bakelite, one of the first completely synthetic plastics to see commercial use (circa 1910).
- A natural resinous polymer called lignin has a cross-linked structure similar to bakelite.
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Polysaccharides
- The most important compounds in this class, cellulose, starch and glycogen are all polymers of glucose.
- As a polymer of glucose, cellulose has the formula (C6H10O5)n where n ranges from 500 to 5,000, depending on the source of the polymer.
- Cellulose is commonly accompanied by a lower molecular weight, branched, amorphous polymer called hemicellulose.
- Glycogen is the glucose storage polymer used by animals.
- Cellulose Nitrate, first prepared over 150 years ago by treating cellulose with nitric acid, is the earliest synthetic polymer to see general use.
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Regio and Stereoisomerization in Macromolecules
- The reasons for this regioselectivity will be discussed in the synthetic methods section.
- If the polymer chain is drawn in a zig-zag fashion, as shown above, each of the substituent groups (Z) will necessarily be located above or below the plane defined by the carbon chain.
- Consequently we can identify three configurational isomers of such polymers.
- Many common and useful polymers, such as polystyrene, polyacrylonitrile and poly (vinyl chloride) are atactic as normally prepared.
- The properties of a given polymer will vary considerably with its tacticity.
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Properties of Macromolecules
- As noted above, synthetic HDPE macromolecules have masses ranging from 105 to 106 amu (LDPE molecules are more than a hundred times smaller).
- Natural rubber is a completely amorphous polymer.
- Tm and Tg values for some common addition polymers are listed below.
- Rubber is a member of an important group of polymers called elastomers.
- This property is important in applications such as gaskets and O-rings, so the development of synthetic elastomers that can function under harsh or demanding conditions remains a practical goal.
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Polymers
- The terms polymer and monomer were derived from the Greek roots poly (many), mono (one) and meros (part).
- Recognition that polymeric macromolecules make up many important natural materials was followed by the creation of synthetic analogs having a variety of properties.