Chapter 16 Polymerization

Question 1

Formation of Polyesters

Answer 1

• Addition polymerisation has been covered in reactions of alkenes
  
  • They are made using monomers that have C-C double bonds joined together to form polymers such as (poly)ethene
• Condensation polymerisation is another type of reaction and is used in the making of polyesters
  
  • A small molecule (eg. a water molecule) is lost when the monomers join together to form a polyester
  • Polyesters contain ester linkages

Question 2

This polymer structure shows an ester functional group linking monomers together

Answer 2

Question 3

Formation of polyesters

Answer 3

• A diol and a dicarboxylic acid are required to form a polyester
  
  • A diol contains 2 -OH groups
  • A dicarboxylic acid contains 2 COOH groups
  • When the polyester is formed, one of the -OH groups on the diol and the hydrogen atom of the -COOH are expelled as a water molecule (H₂O)

Question 4

Expulsion of a water molecule in this condensation polymerisation forms the polyester called Terylene (PET)

Answer 4

Question 5

Hydroxycarboxylic acids

Answer 5

• A single monomer containing both of the key functional groups can also be used for making polyesters
• These monomers are called hydroxycarboxylic acids
  
  • They contain an alcohol group (-OH) at one end of the molecule while the other end is capped by a carboxylic acid group (-COOH)

Question 6

Both functional groups are needed to make a polyester are from the same monomer

Answer 6

Question 7

Amide link

Answer 7

• Polyamides are also formed using condensation polymerisation

Question 8

what are required to form a polyamide

Answer 8

• A diamine and a dicarboxylic acid
• A diamine contains 2 -NH₂ groups
• A dicarboxylic acid contains 2 -COOH groups
• Dioyl dichlorides can also used to react with the diamine instead of the acid
  
  • A dioyl chloride contains 2 -COCl groups
• This is a more reactive monomer than dicarboxylic acid. However, a more expensive alternative

Question 9

The monomers for making polyamides (diagram)

Answer 9

Question 10

Nylon 6,6 is a

Answer 10

• synthetic polyamide
• Its monomers are 1,6-diaminohexane and hexane-1,6-dioic acid
  
  • The ‘6,6’ part of its name arises from the 6 carbon atoms in each of Nylon 6,6 monomers

Question 11

Nylon 6,6 is a

Answer 11

• synthetic polyamide
• Its monomers are 1,6-diaminohexane and hexane-1,6-dioic acid
  
  • The ‘6,6’ part of its name arises from the 6 carbon atoms in each of Nylon 6,6 monomers

Question 12

Kevlar

Answer 12

• The polymer chains are neatly arranged with many hydrogen bonds between them
• This results in a strong and flexible polymer material with fire resistance properties
• These properties also lend Kevlar to a vital application in bullet-proof vests
• The monomers used to make Kevlar
  
  • 1,4-diaminobenzene
  • Benzene-1,4-dicarboxylic acid

Question 13

Kevlar is made using a diamine and dicarboxylic acid monomers(diagram)

Answer 13

Question 14

Aminocarboxylic acids

Answer 14

• Molecules like this are called amino carboxylic acids
• They are able to polymerise to form a structure similar to Nylon 6,6
• They are able provides both of the function groups necessary for an amide/peptide link

Question 15

6-aminohexanoic acid can be polymerised to make the synthetic polymer Nylon 6,6

Answer 15

Question 16

Protein hydrolysis

Answer 16

• Proteins (polypeptides) can be broken down into its constituent amino acids
• This process occurs through a hydrolysis reaction

Question 17

Making Proteins

Answer 17

• Proteins are vital biological molecules with varying functions within the body
• They are essentially polymers made up of amino acid monomers
• Amino acids have an aminocarboxylic acid structure
• Their properties are governed by a branching side group - the R group

Question 18

Different amino acids are identified by

Answer 18

• their unique R group
• The names of each amino acid is given using 3 letters
• For example Glutamine is known as ‘Gln’
• Dipeptides can be produced by polymerising 2 amino acids together
  
  • The amine group (-NH₂) and acid group (-COOH) of each amino acid is used to polymerise with another amino acid

Question 19

• Polypeptides are made through polymerising more than 2 amino acids together (diagram)

Answer 19

Question 20

Deducing the Repeat Unit of a Condensation Polymer

Answer 20

• In condensation polymerisation the monomers either contain 2 of the same functional group or one single monomer has both functional groups needed for polymerisation
  
  • For example Diamine and dicarboxylic acid
  • Or an aminocarboxylic acid
• When presented with 2 monomers there are steps to take in order to deduce the repeat unit of a condensation polymer

Question 21

Identifying Monomers in Condensation Polymers

Answer 21

• When a section of polymer is presented, the monomers can be identified by considering the small molecules expelled from the monomers
• If a water molecule is expelled, the -OH must have been from an acid group
• The hydrogen atom may be from an amine group of a monomer.
• If the molecule was hydrochloric acid (HCl), a dioyl chloride monomer may have been used

Question 22

Predicting Type of Polymerisation

Answer 22

• When a set of monomers are given in an exam question, the type of polymerisation can be determined
• Firstly, it’s important to identify the key functional groups in the monomers

Question 23

Addition polymerisation

Answer 23

• If the monomer/s contain a C=C double bond, they will polymerise through addition polymerisation
• The double bond can open up in order to add more monomers either side of the starting monomer
• This type of polymerisation makes (poly)alkenes

Question 23

Addition polymerisation

Answer 23

• If the monomer/s contain a C=C double bond, they will polymerise through addition polymerisation
• The double bond can open up in order to add more monomers either side of the starting monomer
• This type of polymerisation makes (poly)alkenes

Question 24

(Poly)alkenes can be produced if there are

Answer 24

* 2 or more alkene monomers as well * When more than one monomer is used for addition polymerisation, the resulting product is known as a copolymer

Question 25

**Monomers for condensation polymers table**

Answer 25

Question 26

**Identifying addition polymerisation**

Answer 26

* The polymer backbone of an addition polymer does not contain functional groups * The backbone of the polymer is generally a chain of carbon atoms * There may be sidechains branching off from the backbone * Some examples of side chains are benzene rings, nitrile groups (-CN) and halogen atoms (-F/-Cl/-Br/-I)

Question 27

**Identifying condensation polymerisation**

Answer 27

* A condensation polymer can be identified by functional groups on the polymer backbone * Polyesters contain ester links and polyamides contain amide/peptide link on the backbone itself

Question 28

**Hydrolysis of polyesters**

Answer 28

* Ester linkages can also be degraded through hydrolysis reactions * Acid hydrolysis forms the alcohols and carboxylic acids that were used to form the polyesters

Question 29

**Biodegradable polymers**

Answer 29

* Both polyesters and polyamides can be broken down using hydrolysis reactions * This is a major advantage over the polymers produced using alkene monomers (polyalkenes) * When polyesters and polyamides are taken to landfill sites, they can be broken down easily and their products used for other applications

Question 30

**Hydrolysis of polyamides (acidic hydrolysis)**

Answer 30

* In **acidic hydrolysis**, acid (such as hydrochloric acid) acts as the catalyst * Polyamides are heated with dilute acid * This reaction breaks the polyamide into carboxylic acid molecules and ammonium chloride ions

Question 31

**Hydrolysis of polyamides(**Alkaline hydrolysis)

Answer 31

* The polyamide is heated with a species containing hydroxide ions (eg. sodium hydroxide) * This breaks the polymer into the sodium salts of its monomers (dicarboxylic acids and diamines) * If the poly amide link used an aminocarboxylic acid as the monomer, then a sodium salt of the original amino acid is reformed

Question 32

***When polyamides are degraded by hydrolysis, carboxylic acids and amines are formed***

Answer 32

Question 33

**Disadvantages of photo degradability**

Answer 33

* Despite this ability being a great advantage of polyesters and polyamides, it may pose a problems when the polymers are repurposed * When applied to a new use, the biodegradability could give a weaker polymer * Breaking down polymers also poses another challenge * Once used, polymeric materials are taken to landfill sites where many other materials are piled on top of each other * This could mean that photodegradable polyesters or polyamides do not have access to UV light in order to break down naturally

Question 34

**Photodegradation of Polymers**

Answer 34

* Polyesters and polyamides are biodegradable polymers for a number of reasons * One such reason is their ability to breakdown with the use of light * Carbonyl groups (C=O) along polymer chains are able to absorb energy from the Electromagnetic Spectrum * In particular Ultraviolet (UV) light * Absorbing UV light weakens the carbonyl areas of polymers and breaks them down into smaller molecules

Question 35

Recycling plants can burn used

Answer 35

plastic materials * The energy released from burning can be used to generate electricity * Burning plastics in oxygen releases carbon dioxide and water (complete combustion) which can contribute to global warming

Question 36

* Many of the polymers in use have been produced through addition polymerisation of alkenes

Answer 36

* The (poly)alkene chains are non-polar and saturated * This makes them chemically inert and therefore non-biodegradable * (poly)alkenes can be melted and recycled into new uses * However, even in the new applications, the (poly)alkenes are not biodegradable