Polyesters and polyamides

Condensation Polymerisation In condensation polymerisation there are two different monomers that add together and a small molecule is usually given off as a side-product e.g. H2O or HCl. The two most common types of condensation polymers are polyesters and polyamides which involve the formation of an ester linkage or an amide linkage. The monomers usually have the same functional group on both ends of the molecule e.g. di-amine, di carboxylic acid, diol, diacyl chloride. Carboxylic Acid + Alcohol
Ester + water Acyl chloride + Alcohol
Ester + HCl Carboxylic Acid + Amine
amide + water Acyl chloride + Amine
amide + HCl Forming polyesters and polyamide uses these reactions we met earlier in the course dicarboxylic acid + diol
poly(ester) + water diacyl dichloride + diol
poly(ester) + HCl dicarboxylic acid + diamine
poly(amide) + water If we have the same functional group on each end of molecule we can make polymers so we have the analogous equations: diacyl dichloride + diamine
poly(amide) + HCl n + n OH CH2CH2 OH + 2n-1 H2O Terylene- a common polyester The -1 here is because at each end of the chain the H Terylene fabric is used in clothing, tire cords and OH are still present Ethane-1,2-diol Benzene-1,4-dicarboxylic acid C O OH C O OH 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. C (CH2 )3 O C O Cl Cl OH OH C (CH2 O )3 O C O O + n n n + 2n-1 HCl Pentanedioyl dichloride Benzene-1,4-diol n C C O O O CH2 CH2 O N Goalby chemrevise.org 2 C (CH2 )4 O C O OH OH N H (CH2 )6 N H H H C (CH2 )4 O C O N H (CH2 )6 N H n n + n + 2n-1 H2O Nylon 6,6 – a common polyamide The 6,6 stands for 6 carbons in each of the monomers. Different length carbon chains produce different polyamides hexanedioic acid Hexane-1,6-diamine 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 3 repeating units C O OH H2N 3 repeating units N C O N C O N H H H C O Chemical reactivity of condensation polymers polyesters and polyamides can be broken down by 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 HO2C CO2H H2N NH2 C C O N N H H O n + n + 2n-1 H2O n Kevlar- a common polyamide The reactivity can be explained by the presence of polar bonds which can attract attacking species such as nucleophiles and acids N Goalby chemrevise.org Condensation polymers may be photodegradable as the C=O bond absorbs radiation.