Polymerisation Flashcards
What is a peptide bond
The -CONH- link (amide link) between amino acid residues in a peptide or protein.
A large protein molecule, formed by condensation polymerisation can contain thousands of amino acid monomers. As each amino acid monomer joins the chain, an amide bind ( or peptide bond) forms and an H2O molecule is also produced.
What is a condensation reaction
A reaction in which two organic molecules join together and in the process eliminate a small molecule such as H2O or HCl.
We can think of it as an addition reaction followed by an elimination reaction.
How can we recognise condensation polymerisation
We can recognise condensation polymerisation by its monomers that contain two different functional groups capable of reacting with each other. This can occur in two ways:
- the two different functional groups are found within the same molecule, as in amino acids. Each amino acid monomer has its basic -NH2 functional group and an acidic -COOH functional group
- the two different functions groups are found in two different molecules. For example, nylon 6,6 is made from two different monomers: one monomer has two -NH2 functional groups and the other monomer has two -COOH functional groups.
Condensation polymerisation also leads to the formation of small molecules such as H2O and HCl.
What is a polyamide
Polyamides are polymers made in the condensation polymerisation reaction between a diamine and a dicarboxylic acid (or a dioyl chloride) or between amino acids.
What is nylon and how is it made
Nylon is a polyamide. Nylon can be made from a variety of monomers but all monomers are made in reactions between the amine group (-NH2) and a carboxylic acid (-COOH) or the more reactive acyl chloride (-COCl)
For example 1,6-diaminohexane reacts with hexanedioc acid to make nylon 6,6.
The numbers used in nylon 6,6 refer to the number of carbon atoms in each monomer unit.
Hexanedioyl dichloride ClOC(CH2)4COCl can be used as a more reactive but more expensive monomer than hexanedioc acid
Describe the uses of nylon
Nylon’s low density], its strength and its elasticity make it a very useful fibre in the clothing industry. These properties also make it ideal for climbing ropes.
During the manufacturing process, the nylon is forced out of nozzles and pulled into long fibres. This is called cold drawing. It lines up the nylon polymer chains along the lengths of a fibre. Strong hydrogen bonds form between neighbouring chains, accounting for nylons high tensile strength and elasticity.
Describe what Kevlar is and how it is formed
Kevlar is a polyamide containing benzene rings. The monomers that make Kevlar are an aryl diamine and an aryl dicarboxylic acid or a dioyl chloride.
The long linear polymer chains of Kevlar can line up next to each other in a regular pattern. This results in extensive hydrogen bonding between the polymer chains of Kevlar,
Describe the functions of Kevlar
Kevlar is strong but also flexible. It is also resistant to fire and abrasion. It has these properties because of its structure.
The exceptional properties of Kevlar have also led to its use in making bulletproof vests, ropes, fire-protective clothing and modern leathers worn by motorcycle riders. The polymer is also used to reinforce other materials such as rubber in tyres.
Give example of polyamides
Proteins have their monomer bonded to each other via amide bonds (or peptide bonds). This means that polypeptides and proteins are a type of polyamide,
What is an amino acid residue
Amino acid residue: the individual units of the amino acids that make up a polypeptide or protein.
What does the structure of a protein determine
Proteins may contain one or more polypeptide chains. Each protein has its own unique function because each protein has its own unique 3D shape.
The primary structure of a polypeptide or protein is the order in which the amino acids are linked together.
The structure of a protein:
- Is written with the a,ion acid’s numbered from the N-terminal end.
- determines the way that the proteins fold to form its unique shape
- Is held together by covalent bonds. These bonds are found within the amino acid residues and between the residues as amides (or peptide) bonds.
What is a polyester
A polyester is a polymer whose monomers are bonded to each other via the ester link, COO.
Esters are made by reacting carboxylic acids with alcohols.
Carboxylic acid + alcohol ➡️ ester + water
Therefore polyester can be made by reacting dicarboxylic acids with diols.
Give examples of two polyesters
The most common polyester is terylene. Terylene is made from benzene -1,4-dicarboxylic acids and ethane-1,2-diol. The conditions required are a catalyst such as antimony (III) oxide and heat.
Poly(lactic acid), PLA is another polyester, however polyester is made using just one monomer, lactic acid. Its systematic name is 2-hydroxypropanoic acid. The monomer contains the carboxylic acid and alcohol (hydroxyl) groups within each molecule.
Why are poly(alkene)s non-biodegradable
Poly(alkene)s such as poly(ethene) and poly(propene) are chemically inert because their polymer chains are non-polar, saturated hydrocarbons like giant alkane molecules. This makes them non-biodegradable.
However chemists have developed degradable polymers to help solve the disposal problem. These are biodegradable polymers and photodegradable polymers.
Polyalkenes biodegrade very slowly. Explain why by referring to the structures of the polymers.
C-C bonds are non polar/ have no dipole so cannot be hydrolysed.
Some polymers will degrade in the environment. Describe two processes by which this occurs
Hydrolysis using acid/base/alkali/enzymes
Action of UV light
Give an example of a synthetic polyamide
Nylon/Kevlar
Give an example of a synthetic polyester
Terylene
Give an example of a conducting polymer
Poly acetylene/Polyethyne
Give an example of a non-solvent based adhesive
Epoxyresins/Superglue
By reference to a physical or chemical property. Suggests one advantage of a conducting polymer when compared with metals
Less dense
Describe what is meant by each of these terms:
*Primary structure
* Secondary structure
* Tertiary structure
EPrimary structure: sequence of amino acids
Secondary structurally : alpha helix or beta sheet.
Tertiary structure
Explain why polyamides and polyesters normally biodegrade more readily than polyalkenes.
Polyalkenes c-c bonds are non-polar so cannot be hydrolysed but polyamides can be broken down by hydrolysis.
Name the forces or bonds responsible for the stabilisation of the secondary structure of a protein molecule and identify the group of atoms within the protein molecule that are held together by these forces or bonds.
Hydrogen bonds between C=O and N-H.
Define buffer solution
Allows only small changes in pH/resists changes in pH when small amounts of acid/alkali are added.
Describe the meaning of isoelectric point (1)
The pH at which an amino acts as a zwitterion. Or the pH at which an amino acid has no overall charge.
Explain why condensation polymers normally biodegrade more readily than addition polymers (1)
condensation polymers can be hydrolysed but addition polymers cannot.
