Kevlar^® is a material used in bullet-proof vests.

(i)     Deduce the products formed by a condensation polymerization reaction of the monomers benzene-1,4-diamine and benzene-1,4-dicarbonyl chloride to form Kevlar^®.

(ii)     Describe the factors which account for the inherent strength of Kevlar^®.

(iii)     Outline why Kevlar^® can dissolve in concentrated sulfuric acid.

(i)      ;

Brackets or n not necessary but continuation bonds must be shown.

Do not penalise if CO and NH are in cis configuration.

HCl;

Allow correct name for M2.

(ii)     Kevlar^® (molecules) have strong covalent bonds (so hard to break);

(large number of) hydrogen bonds between C=O and NH groups;

CO/NH groups trans to each other so orientation maximizes interactions/helps packing/produces more ordered structure / $\pi$-bonding/aromatic stacking interactions between benzene rings in neighbouring strands / OWTTE;

(iii)     intermolecular forces/hydrogen bonds broken / nitrogen and oxygen atoms become protonated / reverses condensation process / OWTTE;

In (c) (i), continuation bonds were frequently omitted and ${{\text{H}}_{\text{2}}}{\text{O}}$ was often stated incorrectly instead of HCl. In (ii) although some candidates mentioned the hydrogen bonding network in Kevlar^® often they did not state that these intermolecular forces are between the C=O and NH groups. (iii) was generally answered correctly.