polymer

Examples of polymer in the following topics:

• 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.

• 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.
  • Unlike simpler pure compounds, most polymers are not composed of identical molecules.
  • 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.

• Thermosetting vs. Thermoplastic Polymers

  • Most of the polymers described above are classified as thermoplastic.
  • Another group of polymers, characterized by a high degree of cross-linking, resist deformation and solution once their final morphology is achieved.
  • 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.
  • A natural resinous polymer called lignin has a cross-linked structure similar to bakelite.

• 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.
  • Many polymers are made entirely from hydrocarbons.
  • Low Density Polyethylene (LDPE) polymers are among the most common types of synthetic organic polymers, which are often found in households.
  • Nylon is one of the most commonly-used polymers.

• Block Copolymerization

  • The unquenched polymer has been termed a living polymer, and if additional styrene or a different suitable monomer is added a block polymer will form.

• 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.

• Synthesis of Addition Polymers

  • All the monomers from which addition polymers are made are alkenes or functionally substituted alkenes.
  • A general diagram illustrating this assembly of linear macromolecules, which supports the name chain growth polymers, is presented here.
  • Since a pi-bond in the monomer is converted to a sigma-bond in the polymer, the polymerization reaction is usually exothermic by 8 to 20 kcal/mol.

• Polymers

  • The terms polymer and monomer were derived from the Greek roots poly (many), mono (one) and meros (part).

• Biodegradable Polymers

  • Structures for the these polymers and their monomer precursors are shown below.
  • PLA is actually a polymer of lactic acid, but the dimeric lactide is used as the precursor to avoid the water that would be formed in a direct poly-esterification.
  • Blends of PLA with polymers such as ABS have good form-stability and visual transparency, making them useful for low-end packaging applications.
  • In contrast to P(3HB), the polymer of 4-hydroxybutyrate, P(4HB), is elastic and flexible with a higher tensile strength.
  • The following table lists some of the properties of these homo-polymers and co-polymers.

• Regio and Stereoisomerization in Macromolecules

  • 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.