Polymer Molecules

Condensation and Addition . Proteins and Enzymes, Index

Condensation polymers; starch, polyamides and polyesters

Proteins

Enzymes

Linear and cross-linked polymers

Specialised polymers

Consumption of plastic

History of Plastics Condensation Polymers

Polymers are very large molecules made by joining small molecules called , into long chains or networks. Condensation polymers are made from monomers with two functional groups which can be the same or different.

Starch is made by polymerisation of about 300 glucose molecules

H H H O O O O O O O + H H H H2O

Glucose Glucose Maltose

The adding together of monomers O O O to make a is called polymerisation. Starch Polyesters and Polyamides

Polyesters are examples of condensation polymers and are formed when a carboxylic acid reacts with an alcohol monomer.

O O O O O O O O H H C C C C C C H O O H O O O O Diol Diacid monomer monomer

Polyamides (eg and Kevlar) are formed when an amide link is formed by the reaction of an amino functional group with a carboxyl group.

O H H O H O C C H N N H H O O H N C + water Diacid Diamine Amide link monomer monomer Condensation Polymers

HO O O

O OH O O + O CH2 CH2 O O HO CH2 CH2 OH

Polyester, e.g. terylene Polyesters are used as textiles and resins. The latter have 3D structures, unlike textiles, which have a linear structure. Polyamide, e.g. nylon, an important engineering plastic. It’s strength due to hydrogen bonding between the linear polymer chains. Engineering plastics are a group of plastics materials that exhibit superior mechanical and thermal properties H O O H H O O

H C (CH ) C (CH ) 2N (CH2)6 N 2 4 C N (CH2)6 N 2 4 C H 3 Protein Polymers All proteins contain the elements C,O,H, N. They are condensation polymers, made by amino acids linking together. An amine group of one molecule links to the carboxyl group of another molecule to form an amide or peptide bond.

The body cannot make every type of amino acids that it needs. So our diet must contain essential amino acids. (about 10 of them). We synthesis the others.

Amino Acids

H R O R Most proteins contain 20+ different amino H N C C O H NH2CHCOOH acids H When R is Hydrogen, the amino acid is glycine (Gly) (aminoethanoic acid)

When R is CH3, the amino acid is alanine (Ala) (2-aminopropanoic acid) Protein Polymers

H O H O H H N C O O H H N C O H C N Amino acid monomer Peptide link

CH3 H CH3

H2NCHCOOH + H2NCHCOOH + H2NCHCOOH alanine glycine alanine

CH3 H CH3

H2NCHC NCHC NCHCOOH

O H O H Tripeptide, ala-gly-ala Polypeptide chain can have 10000 amino acids Protein Digestion

Proteins are broken down during digestion. Digestion involves the hydrolysis of proteins to form amino acids

R1 R2 R3

Protein H2NCHC HNCHC HNCHC O H

O O O

2 x H-O-H added and the peptide bond breaks here

Peptidase enzyme

R1 R2 R3 Amino H2NCHC O H HNCHC O H HNCHC O H acids O H O H O Protein Structures

Some proteins are composed of a single polypeptide chain, but many consist of two or more polypeptide chains.

Proteins are classified according to their shape into fibrous and globular proteins. Fibrous proteins These have their polypeptide chains interwoven. The polypeptide chains are held together by hydrogen bonding, between the N-H and the C=O groups. This gives these proteins their properties of toughness, insolubility, and resistance to change in pH and temperature. So they are found in skin,tissue, (collagens), hair, nails (keratins). Globular proteins Proteins which operate within cells need to be soluble. The polypeptide chains are coiled together in spherical shapes. E.g. Haemoglobin and many hormones. e.g. Insulin, was the first protein structure to be worked out. Enzymes are globular proteins. Protein Structures

Silk is a typical example of a fibrous protein.

Silk

This view shows This view shows the the individual protein chains contain 2 atoms in the different amino acids. protein chains. Protein Structures

Albumen, in egg white, is a globular protein..

Albumen

backbone view atom view Protein Structures Enzymes are globular proteins. The structure of amylase is shown below.

Starch molecule in the enzyme’s active site. Enzyme Activity Enzymes catalyse chemical reactions in the body. Each enzyme has a unique shape held together by many weak bonds. Changes to pH and temperature can denature the enzyme. This changes the enzymes shape stops it working properly. Narrow optimum range

Enzyme activity

Temp or pH The bonds that hold most biological enzymes are broken around 60oC. Enzyme Activity, Lock and Key The critical part of an enzyme molecule is called its active site. This is where binding of the substrate to enzyme occurs and where catalysis takes place. Most enzymes have one active site per molecule. Substrate

Enzyme Enzyme Activity, Lock and Key

Substrate

Enzyme

Active site Enzyme Activity, Lock and Key

The substrate becomes activated

Enzyme Enzyme Activity, Lock and Key

The substrate becomes activated

Enzyme Enzyme Activity, Lock and Key

The complex molecule splits

Enzyme Enzyme Activity, Lock and Key

The complex molecule splits

Enzyme Linear Addition Polymers

H H H H

C C C C polythene H H H H

Under the right conditions ethene molecules can be made to join together.

The double bond must be broken for this to happen Polymerisation

The ethene molecule is called a monomer. Adding monomers together makes a polymer, in this case, Polythene. (a linear addition polymer)

H H H H H H H H H H H H C C C C C C C C C C C C

H H H H H H H H H H H H

Polythene can be made photodegradable by putting some C=O groups into the chain Other Addition Polymers By replacing a H in the ethene molecule, further addition polymers can be made. Three monomers are shown:

F F C6H5 H Cl H

C C C C C C

F F H H H H

Tetrafluoroethene Phenylethene Chloroethene (teflon) () (P.V.C.) Non-stick coating on Expanded foam Artificial leather frying pans for packaging Cross-Linked Polymers

CH2 CH2 CH2 CH2

OH OH

H2C HO CH2 HO CH2

CH2 CH2 CH2 CH2

HO H2C H2C Bakelite When polymer chains are linked by covalent bonds the polymer is then described The resulting cross-linked structure as cross linked. means that the polymer is hard, rigid and heat resistant. It is a thermosetting plastic. Specialised Polymers

Kevlar is an aromatic polyamide. Both monomers are aromatic. O

N H O H O N N

O H H

N Hydrogen bonding N O H

O N H

The polymer chains are long, flat, and lined up in a regular pattern held by hydrogen bonding. Used in bullet proof vests, ropes and fire proof clothing. Uses of Kevlar Uses include: – as a substitute for steel – Fabric for windsurfing sails and protective clothing – Bullet proof vests and body armour – Reinforcing fibre in composites, often with carbon fibre.

Disadvantages of Kevlar fibres: – they are difficult to cut – It is much weaker in compression – Very prone to UV degradation Specialised Polymers

Poly(ethenol) is an addition polymer. It is made by converting an existing polymer which has ester side groups with hydroxyl groups. The polymer can be made to be water soluble, by controlling the amount of ester exchange, 90% ester exchange is soluble in cold water. Soiled hospital laundry can be collected in bags made from poly(ethenol). CH CH 3 3 H H C O C O Ester exchange O O O O + methanol CH CH CH CH CH2 CH2 CH2 CH2 Polyethenyl ethanoate Polyethenol (polyvinyl alcohol)

Both hydrogen bonding and van der Waals’ forces operate between poly(ethenol) molecules. The stronger these forces the less soluble the polymer. <90% of –OH replacement are soluble in cold water. Specialised Polymers • Most plastics are not biodegradable. • Most polymers, including , , polyamides and polycarbonate, are highly resistant to microbial attack. • Natural polymers are generally more biodegradable than synthetic polymers. • Polymers containing an ester linkage, especially aliphatic polyesters, are potentially biodegradable Biodegradable polymers include poly(lactic acid) (PLA) which is made from the self-condensation of lactic acid. PLA breaks down into lactic acid which can be metabolised and has. found uses in, drug delivery systems and wound healing. Biopol is another biodegradable plastic. Specialised Polymers Biopol This plastic is biodegradable. This plastic is produced by the fermentation of ethanoic and propanoic acids by bacteria. Biopol is therfore unsuitable For foods requiring a long shelf life. High production costs and the recycling of polymers has meant that Biopol has lost its importance.

CH3 H O C2H5 H O

HO C C C OH + HO C C C OH

H H H H

CH3 H O C2H5 H O

O C C C O C C C O

H H H H Specialised Polymers

Poly(vinylcarbazole) This polymer can conduct electricity when exposed to light. It is widely used in photocopying machines as a replacement for selenium, which is poisonous.

N N N H H

H C C C C C H 3 H H H H H UK Consumption of Plastics by Type

OTHERS L/LLDPE 20.7% 19.3%

UP Resin 1.8% HDPE 11.3% PET/PBT 5.5% ABS/SAN 2.1% PA PP PVC 16.1% 1% 16% PS EPS 5.2% 1.2%

47% of the polymer used is polyolefins, based on ethylene or propylene

UK Consumption of Plastics by Market

Others 18% Medical 2% Packaging Transport 38% 7%

Furn/House 7% Electrical 6% Construction 22%