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6.2.3 Revision Guides Polyesters and Polyamides

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6.2.3 Revision Guides Polyesters and Polyamides 6.2.3 Polyesters and Polyamides There are two types of polymerisation : addition and condensation Addition Polymerisation An addition polymer forms when unsaturated Poly(alkenes) are chemically inert due to the strong C-C monomers react to form a polymer and C-H bonds and non-polar nature of the bonds and Monomers contain C=C bonds therefore are non-biodegradable. Chain forms when same basic unit is repeated over and over. It is best to first draw out H CH 3 You should be able e.g. For but-2-ene the monomer with groups H CH3 to draw the polymer of atoms arranged around CC CC repeating unit for any H3C CH CH CH3 the double bond alkene H3C H CH 3 H n Condensation Polymerisation In condensation polymerisation there are two different monomers The two most common types of that add together and a small molecule is usually given off as a condensation polymers are side-product e.g. H 2O or HCl. polyesters and polyamides which involve the formation of an ester The monomers usually have the same functional group on both ends linkage or an amide linkage. of the molecule e.g. di-amine, di carboxylic acid, diol, diacyl chloride. Forming polyesters and polyamide uses these reactions we met earlier in the course Carboxylic Acid + Alcohol Ester + water Carboxylic Acid + Amine amide + water Acyl chloride + Alcohol Ester + HCl Acyl chloride + Amine amide + HCl If we have the same functional group on each end of molecule we can make polymers so we have the analogous equations: dicarboxylic acid + diol poly(ester) + water dicarboxylic acid + diamine poly(amide) + water diacyl dichloride + diol poly(ester) + HCl diacyl dichloride + diamine poly(amide) + HCl Using the carboxylic acid to make the ester or amide would need an acid catalyst and would only give an equilibrium mixture. The more reactive acyl chloride goes to completion and does not need a catalyst but does produce hazardous HCl fumes. Terylene- a common polyester O O O O n + n C C O CH 2 CH 2 O + 2n-1 H O C C OH CH 2 CH 2 OH 2 n OH OH Ethane-1,2-diol The -1 here is because at Benzene-1,4-dicarboxylic acid each end of the chain the H Terylene fabric is used in clothing, tire cords and OH are still present O O O O n C (CH 2)3 C + n OH OH + 2n-1 HCl C (CH 2)3 C O O Cl Cl n Pentanedioyl dichloride Benzene-1,4-diol N Goalby chemrevise.org 1 Nylon 6,6 - a common polyamide O O O O H H N (CH 2)6 N n C (CH 2)4 C + n C (CH 2)4 C N (CH 2)6 N + 2n-1 H O H H 2 OH OH hexan edioic acid H H Hexane-1,6-diamine n The 6,6 stands for 6 carbons in each of the monomers. Different length carbon chains produce different polyamides Kevlar- a common polyamide O O n HO 2C CO 2H + n H2N NH2 + 2n-1 H O N N C C 2 H H n Note on classification for condensation polymers If asked for type of polymer : It is polyamide or polyester Whereas type of polymerisation is condensation It is also possible for polyamides and polyesters to form from one monomer, if that monomer contains both the functional groups needed to react H O H O H O HO O CH C HO CC O CC O CC OH CH CH CH H3C OH 3 3 3 3 repeating units 2-hydroxypropanoic acid poly(lactic acid) lactic acid O O O O H2N C N C N C N C OH H H H 3 repeating units Chemical reactivity of condensation polymers The reactivity can be explained by the presence of polar bonds which can attract attacking species polyesters and polyamides can be broken down by such as nucleophiles and acids hydrolysis and are, therefore, biodegradable Polyesters can be hydrolysed by acid and alkali With HCl a polyester will be hydrolysed and split up in to the original dicarboxylic acid and diol With NaOH an polyester will be hydrolysed and split up into the diol and dicarboxylic acid salt. Polyamides can be hydrolysed by aqueous acids or alkalis. With HCl an polyamide will be hydrolysed and split up in to the original dicarboxylic acid and diamine salt With NaOH an polyamide will be hydrolysed and split up into the diamine and dicarboxylic acid salt Condensation polymers may be photodegradable as the C=O bond absorbs radiation. N Goalby chemrevise.org 2.
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