Polymers & Synthesis


Amino Acids

  • Amino acids form polypeptides and proteins, vital for hormones and enzymes.
  • The body has a mixture of 20 amino acids that can be assembled into proteins:
    -General formula of alpha-amino acid: RCH(NH2)COOH
  • So the amino acid has a basic (NH2) and an acidic (COOH) group.
  • These can react with each other to form an internal salt, known as a ZWITTERION.
  • A proton is transferred from the acidic COOH to the basic NH2.
  • But the zwitterion has no overall charge due to cancelling out.
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  • The zwitterion has no overall charge, at the isoelectric point.
  • The isoelectric point varies with each amino acid.
  • Amino acids are amphoteric, reacting with both acids and bases.
  • At an acidic pH, the amino acid behaves as a base and accepts H+ forming a positive ion.
  • At an alkaline pH, it behaves as an acid and dontates H+ forming a negative ion. 
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Polypeptides & Proteins

  • Amino acids join together by peptide bonds, to form peptides.
  • This is a condensation reaction, where H2O is removed.
  • Two peptides being formed together is called a dipeptide and so on.
  • Proteins are simply long amino acids. generally with 50 amino acids or more. 
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  • Acid hydrolysis:
    -By using an aqueous acid, water is needed to break the bond.
    -The amino acids formed are positively charged due to the presence of H+ from the acid.
  • Alkaline hydrolysis:
    -Solution of aqueous NaOH at 100 degrees C.
    -Broken down into their Na salts (Sort of cut off here but only clear image)
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Optical Isomerism

  • Another form of stereoisomerism, but seperate to E/Z.
  • Arises in molecules that contain a chiral carbon, that is, one that is connected to FOUR different groups of atoms.
  • Two-mirror image arrangements of atoms in space are possible, that are non-superimposable and are called optical isomers - or enantiomers.
  • To draw an enantiomer:
  • These polarise light differently and may have slightly different affects to each other. 
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Condensation polymerisation: polyesters

  • Condensation is the joining of two monomers with the removal of H2O/HCl.
  • There are two different types of polyesters:
    1- Where there are two different monomers, one with two -COOH groups and one with two -OH groups.
    2- Where there is one monomer, with a -COOH and a -OH attached. 
     (Two different monomers)
     (One monomer, COOH and OH) 
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Condensation polymerisation: polyamides

  •  (Amide linkage)
  • The same as before it is possible to form a polyamide by using two different monomers or just the one single monomer:
    -Two different: A molecule with 2 COOH groups, and one with 2 NH2 groups.
    -One single; A molecule that contains both a COOH group and a NH2.
    (Nylon-6,6 formation) 
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Addition & Condensation Polymerisation

  • Addition polymers:
    -Only one monomer used.
    -One product formed.
    -C=C functional group.
    -Forms polyalkene.
  • Condensation:
    -One or two monomers used.
    -Uses COOH/OH or COOH/NH2.
    -Forms the polyester/amide and water.
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Breaking Down Condensation Polymers

  • Hydrolysis of polyesters:
    1-With hot alkali(aq):
    -The sodium salt of the carboxylic acid.
    -The hydroxyl group.
    2-With hot acid(aq):
    -The monomer units.
  • Hydrolysis of polyamides:
    1-With hot alkali(aq):
    -The sodium salt of the dicarboxylic acid.
    -The diamine.
    2-With hot acid(aq):
    -The dicarboxylic acid.
    -An ammonium salt of the diamine.
  • Biodegradable polymers:
    -Made from renewable sources such as corn starch, and break down with water/light to form CO2 and H2O with the presence of bacteria.
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Polyester alkakine hydrolysis:

I cannot find a decent picture of acid hydrolysis of polyamides but basically the diamine has NH3+, that is the hardest bit.

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