condensation polymerisation reactions

what are polymers?

polymers are covalent molecular structures composed of many small molecules joined together to form a long chain of atoms.

polymers are formed by joining together thousands of smaller molecules called…

monomers, through a process called polymerisation

polymer chains are made up of,…

identical segments that are repeated along the length of the molecule. each of these segments called a repeating unit

what are the structural properties of polymers?

the properties of a polymer are determined primarily by the type of monomer used to produce it. However other structural features the properties of the polymer. these factors effect the strength of the intermolecular forces between the polymer chains include the length of the polymer chain, branching of the polymer chain and the cross linking between the polymer chain.

how does length effect the strength of the polymer chain?

as the polymer chain gets longer the strength of the dispersion forces between the neighbour polymer chain increases. This means that the resulting polymer is harder and a more rigid material.

what is branching in a polymer, and how does it form?

branched polymers are formed when some monomers react with sites on the side of the polymer chain instead of the end of the polymer chain. when a monomer joins to the side of the polymer chain it begins a new chain in another direction.

how does branching effect the structural properties of a polymer?

polymer branching changes the properties of the polymer significantly depending on the nature and the extent of the branching. Branching can cause the polymer molecule to be spread further apart, resulting in a less dense material with a greater distance between the polymer chains, the intermolecular interaction between neighbouring chains is weakened, increasing the flexibility of the material.

both straight chained and branched chain polymers exist as….

thermoplastic polymers (as long as there are no covalent cross links between polymer chains

the term plastic…

describes the property of a material, rather than the material itself. a substance is described as plastic if it can be easily moulded

thermoplastic polymers…

soften when heated, which means they can be remoulded or recycled

polymers are only thermoplastics if the bonds between the polymer chains are..

hydrogen bonds, dipole- dipole bonds, or weak dispersion forces, rather than covalent bonds

what happens when thermoplastics are heated?

the molecules in the thermoplastic materials have enough energy to overcome the intermolecular forces and become free to move and slip past one another.

what is cross linking?

this is when the polymer branches are covalently bonded to neighbouring polymer chains. This bonding creates a polymer network.

why can polymer chains with cross linking cannot be liquids?

because the polymer chains are held in the cross linking structure and are unable to flow.

cross linking polymers exist as thermosetting polymers, what does this mean?

thermosetting polymers means that the polymers decompose or burn when heated, rather than melting, and are hard and rigid.

why do thermosetting polymers not soften?

this is because the bonds between the chains are very strong. if the temperature is high enough to break the covalent bonds, the bonds may break at any point, causing the polymer to decompose.

when are. elastomers formed?

they are formed when only occasional cross links are present the chain . the chains in these polymers can still move past each other when stretched, but the cross links return the chains to their original positions once the force causing the stretching is released

How do the cross links stop the elastomers from…

completely melting when heated .

additional polymerisation requires…

monomers that are unsaturated (contain and double or triple carbon bond) during the polymerisation process, the. double or triple bond is broken and single C-C bonds are formed between monomers.

what is required for condensation polymerisation to occur?

the monomers must have ti functional groups, one on each end of the monomer. these functional groups react chemically with the fucntional groups on neighbouring monomers.

what is also produced in a condensation polymerisation reaction?

small molecules, in the reaction to form polyamides an atom for water is produced during each reaction between two functional groups.

what happens when the pair of functional groups react together in a condensation polymerisation reaction?

s new function group is produced that links the monomers. at the same time a small molecule, such as water is produced.

the condensation polymerisation reaction between two amino acids are because of which functional groups?

this can occur between a molecule that contains a carboxyl group (-COOH) and a molecule that contains an amino group (-NH2)

what new functional group is formed during a condensation polymerisation reaction?

an amide (-CONH-) this links the two molecules

why can alpha amino acids undergo condensation reactions with each other?

this is because when the two amino acids react, am amide group is formed that links the molecules together. This amide link is sometimes called the peptide link

what/ where is the peptide bond?

the bond between the carbon and the nitrogen atoms in the amide group is sometimes called a peptide bond.

two amino acids are called?

a dipeptide.

why is there two possible product molecules formed when a dipeptide is formed?

this is because there are two ends of each of the molecules, it depends which sides undergo the reaction and create the peptide bond

what are polypeptides?

they are polymers formed by condensation polymerisation of amino acids. During these reactions amino acids can form long chains

when three amino acids react together…

a tripeptide is formed

what direction are polypeptides arranged in?

from the N-terminus (which is the free amino group) to the C -terminus (which is the free carboxyl group)

a polypeptide constructed from more than 50 amino acids is called a…

protein

explain how proteins are broken down in the body..

water molecules are required to break the peptide bonds. This type of reaction is known as hydrolysis and in this case hydrolysis can be regarded as the reverse reaction to the condensation reactions that formed the protein.