A Level Chemistry Polymers PDF

A LEVEL CHEMISTRY 3.3.12 POLYMERS CONDENSATION POLYMERS There are two types of condensation polymers that we need to know about: O O...

A LEVEL CHEMISTRY 3.3.12 POLYMERS CONDENSATION POLYMERS There are two types of condensation polymers that we need to know about: O O O Polyesters R C O R C O R C O These consist of carbon chains bonded together by ester linkages. O H O H O H Polyamides R C N R C N R C N These consist of carbon chains bonded together by secondary amide linkages. Before we get into the chemistry of these, here’s a few key pieces of info… Monomer: The molecule(s) that react together to form a polymer Polymer: A long-chain molecule made up of repeating units Repeating Unit: The repeating sections of a polymer. Essentially these are the monomer(s). Condensation: A reaction that produces a small molecule as a by-product So, monomers react together in a condensation reaction to form long chain polymers. The repeating units of the polymer are bonded together by either by ester or amide linkages. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.12 POLYMERS POLYESTERS An ester group can be formed by reaction between a carboxylic acid and an alcohol. Here's a reminder of what it looks like… H O R C O C R H Normally esters exist as discrete molecules, crated by reaction between one carboxylic acid and one alcohol molecule. Polyesters are long chain polymers of alternating repeating units bonded together by ester linkages: - C’Acid - Alcohol - C’Acid - Alcohol -C’Acid - Alcohol -C’Acid - Alcohol - To enable this to happen, we need monomers that have two functional groups. To produce polyesters we need a dicarboxylic acid and a diol. O O C R C HO R OH HO OH Dicarboxylic Acid Diol These monomers then react together, end-to-end, to form multiple ester linkages O O O O O O C R C HO R OH C R C HO R OH C R C HO R OH HO OH HO OH HO OH O O O O O O C R C O R O C R C O R O C R C O R O +H2O +H2O +H2O +H2O +H2O AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.12 POLYMERS Terylene A polyester used in clothing H H O O Monomers: HO C C OH n HO OH n H H benzene-1,4-dicarboxylic acid ethan-1,2-diol O O H H Repeating Unit: C C O C C O + nH2O H H n AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.12 POLYMERS POLYAMIDES A (secondary) amide group can be formed by reaction between a carboxylic acid and a primary amine. Here's a reminder of what it looks like… O H R C N R Normally amides exist as discrete molecules, crated by reaction between one carboxylic acid and one primary amine molecule. Polyamides are long chain polymers of alternating repeating units bonded together by ester linkages: - C’Acid - Amine - C’Acid - Amine -C’Acid - Amine -C’Acid - Amine - To enable this to happen, we need monomers that have two functional groups. To produce polyesters we need a dicarboxylic acid and a diamine. O O H H C R C N R N HO OH H H Dicarboxylic Acid Diamine These monomers then react together, end-to-end, to form multiple ester linkages O O H H O O H H O O C R C N R N C R C N R N C R C HO OH H H HO OH H H HO OH O O H H O O H H O O C R C N R N C R C N R N C R C +H2O +H2O +H2O +H2O AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.12 POLYMERS Nylon 6,6 A polyester used in clothing O O H H Monomers: C (CH2)4 C N (CH2)4 N n HO OH n H H hexanedioic acid 1,6-diaminohexane Repeating Unit: O O H H C (CH2)4 C N (CH2)4 N + nH2O n Kevlar A polyester used in clothing, helmets, bullet-proof vests O O H H Monomers: C C N N n HO OH n H H benzene-1,4-dicarboxylic acid 1,4-diaminobenzene Repeating Unit: O O H H + nH2O C C N N n AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.12 POLYMERS Amino Acids are an example of how polyamides can form using only one monomer. Biologists will know these as polypeptides, but they are actually polyamides. Amino acids are able to do this as they have both a carboxylic acid group and an amine group on the same molecule. This allows them to form amide linkages, end to end, to form long polymer chains. There are 20 amino acids in the human body. Each has a different R-group, but the rest of the structure of is the same. O R H Amino Acid: C C N (Monomer) n HO H H Amino acid chain don’t have “repeating units” due to the fact that there are 20 different R-groups. The diagram below shows a chain of 4 amino acids. O R1 H O R2 H O R3 H O R4 H C C N C C N C C N C C N H H H H These amino acid chains (polypeptides) form the basis of proteins. More on this in Section 3.3.13 (Amino Acids, Proteins & D.N.A.) AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.12 POLYMERS HINTS | TIPS | HACKS “n” monomers produce “n” repeating units and “n” H2O’s. Notice how the ends of the repeating units How To Tackle are left with open bonds. When drawing Polymer Questions these, ensure that these two open bonds would link to each other end to end. i.e. they are technically the same bond as each other. Once you have draw your repeating unit, for it to be correct, you should be able to “copy & paste” it end to end and it work as a polymer. You need to be spot repeating units in a section of polymer able to draw the structure repeating units from monomers and vice versa. INTERMOLECULAR FORCES IN POLYMERS R δ+ C O R Polyesters have permanent dipole δ- ))))) forces between the polymer chains, as O well as induced-dipole (Van der Waal’s) ))) )) Oδ- δ+ forces. R C O R δ+ δ- R C N R Polyamides have hydrogen bonding forces between the polymer chains, as δ- O Hδ+ )))))))))) )))))))))) well as induced-dipole (Van der Waal’s) δ+ δ- forces. H O δ- δ+ R N C R AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.3.12 POLYMERS CONDENSATION Vs ADDITION POLYMERS CONDENSATION POLYMERS ADDITION POLYMERS Require two molecules / functional Require only one functional group to groups to form form - C’ acid + alcohol / amine - Alkene Produce H2O as a by-product Produces no by-products Less than 100% atom economy 100% atom economy Polar linkages between repeating Non-polar linkages units Polyesters: Permanent Dipole IFS Induced Dipole IMFs only Polyamides: Hydrogen Bonding BIODEGRADABILITY & DISPOSAL Condensation polymers are biodegradable as they have polar ester / amide links between repeating units. This means that nucleophiles are attracted to these groups and can hydrolyse the bonds to break the polymer down. Addition polymers have no polar linkages between repeating units. This means that nucleophiles cannot hydrolyse them to break the polymer down. Addition polymers may have polar side groups such as C-Cl bonds, but breaking these does not break the chain. DISPOSAL ADVANTAGES DISADVANTAGES Non-biodegradable Biodegradable plastics break Landfill polymers take many years to down relatively quickly break down Expensive process of Recycling Saves on raw materials cleaning, sorting and reforming Provides energy to generate Can produce toxic gases Incineration electricity such as HCl(g) AQA www.chemistrycoach.co.uk © scidekick ltd 2024