monomer

Examples of monomer in the following topics:

• Dehydration Synthesis

  • In doing so, monomers release water molecules as byproducts.
  • In a dehydration synthesis reaction between two un-ionized monomers, such as monosaccharide sugars, the hydrogen of one monomer combines with the hydroxyl group of another monomer, releasing a molecule of water in the process.
  • The removal of a hydrogen from one monomer and the removal of a hydroxyl group from the other monomer allows the monomers to share electrons and form a covalent bond.
  • When the monomers are ionized, such as is the case with amino acids in an aqueous environment like cytoplasm, two hydrogens from the positively-charged end of one monomer are combined with an oxygen from the negatively-charged end of another monomer, again forming water, which is released as a side-product, and again joining the two monomers with a covalent bond.
  • As additional monomers join via multiple dehydration synthesis reactions, the chain of repeating monomers begins to form a polymer.

• Types of Biological Macromolecules

  • Examples of these monomers and polymers can be found in the sugar you might put in your coffee or tea.
  • Regular table sugar is the disaccharide sucrose (a polymer), which is composed of the monosaccharides fructose and glucose (which are monomers).
  • If we were to string many carbohydrate monomers together we could make a polysaccharide like starch.
  • The prefixes "mono-" (one), "di-" (two),and "poly-" (many) will tell you how many of the monomers have been joined together in a molecule.
  • Lipids are not polymers, because they are not built from monomers (units with similar composition).

• Addition Copolymerization

  • Most direct copolymerizations of equimolar mixtures of different monomers give statistical copolymers, or if one monomer is much more reactive a nearly homopolymer of that monomer.
  • In cases where the relative reactivities are different, the copolymer composition can sometimes be controlled by continuous introduction of a biased mixture of monomers into the reaction.
  • Formation of alternating copolymers is favored when the monomers have different polar substituents (e.g. one electron withdrawing and the other electron donating), and both have similar reactivities toward radicals.

• Writing Formulas for Polymeric Macromolecules

  • Here ethylene (ethene) is the monomer, and the corresponding linear polymer is called high-density polyethylene (HDPE).
  • If Y and Z represent moles of monomer and polymer respectively, Z is approximately 10-5 Y.
  • The HDPE molecules, for example, are all long carbon chains, but the lengths may vary by thousands of monomer units.
  • 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.
  • A listing of some important addition polymers and their monomer precursors is presented in the following table.

• Carbohydrate Molecules

  • Lactose is a disaccharide consisting of the monomers glucose and galactose.
  • It is made up of monomers of glucose.
  • Cellulose is made up of glucose monomers that are linked by β 1-4 glycosidic bonds .
  • Every other glucose monomer in cellulose is flipped over, and the monomers are packed tightly as extended long chains.
  • Sucrose is formed when a monomer of glucose and a monomer of fructose are joined in a dehydration reaction to form a glycosidic bond.

• Hydrolysis

  • Hydrolysis reactions result in the breakdown of polymers into monomers by using a water molecule and an enzymatic catalyst.
  • Polymers are broken down into monomers in a process known as hydrolysis, which means "to split water," a reaction in which a water molecule is used during the breakdown .
  • In the hydrolysis reaction shown here, the disaccharide maltose is broken down to form two glucose monomers with the addition of a water molecule.
  • This is the reverse of the dehydration synthesis reaction joining these two monomers.
  • This is the reverse of the dehydration synthesis reaction joining these two monomers.

• Regio and Stereoisomerization in Macromolecules

  • Symmetrical monomers such as ethylene and tetrafluoroethylene can join together in only one way.
  • Monosubstituted monomers, on the other hand, may join together in two organized ways, described in the following diagram, or in a third random manner.
  • Most monomers of this kind, including propylene, vinyl chloride, styrene, acrylonitrile and acrylic esters, prefer to join in a head-to-tail fashion, with some randomness occurring from time to time.
  • Customized catalysts that effect stereoregular polymerization of polypropylene and some other monomers have been developed, and the improved properties associated with the increased crystallinity of these products has made this an important field of investigation.

• Copolymers

  • The following examples refer to a two component system, in which one monomer is designated A and the other B.

• Polymers

  • He formulated a polymeric structure for rubber, based on a repeating isoprene unit (referred to as a monomer).
  • The terms polymer and monomer were derived from the Greek roots poly (many), mono (one) and meros (part).

• Synthesis of Addition Polymers

  • All the monomers from which addition polymers are made are alkenes or functionally substituted alkenes.
  • 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.