Q.How is dacron obtained from ethylene glycol and terephthalic acid ?

Dacron (also called Terylene) is a polyester formed by condensation (step-growth) polymerisation between ethylene glycol and terephthalic acid.

The two monomers are heated together at a high temperature (about 420–460 K) in the presence of a catalyst (e.g., zinc acetate–antimony trioxide mixture). The $-OH$ groups of ethylene glycol react repeatedly with the $-COOH$ groups of terephthalic acid to form ester ($-CO-O-$) linkages, with elimination of a water molecule at each linkage formed, building up a long linear polyester chain:

$n\,HO-CH_2CH_2-OH + n\,HOOC-C_6H_4-COOH \xrightarrow[\Delta]{\text{Zn acetate/Sb}_2O_3} -[-O-CH_2CH_2-O-CO-C_6H_4-CO-]_n- + 2n\,H_2O$ …

Identify this as a polyesterification (condensation) between a diol and a diacid, write the balanced repeat step showing water elimination, an …

• Describing this as an addition reaction rather than a condensation (esterification) reaction.
• Forgetting to show water as the eliminated by-product in the equation. …