Animated Solution for Chemistry - Organic Chemistry: Which among the following is not a polyester ?

Identifying Polyesters

When we dive into the fascinating world of polymers, the nomenclature often gives away the secret to their structure. Take the word polyester, for example. It literally translates to "many esters."

This means that for a polymer to be classified as a polyester, its main chain must be held together by repeating ester linkages. An ester linkage is characterized by the functional group $-C(=O)-O-$. Our mission in this problem is simple: examine the given options and find the imposter—the polymer that lacks this crucial ester bond.

Let's start by looking at PHBV (Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)). This is a specialized, biodegradable polymer synthesized from hydroxy acids. During its formation, the hydroxyl ($-OH$) group of one monomer undergoes a condensation reaction with the carboxylic acid ($-COOH$) group of another. This reaction eliminates a water molecule and forms a classic ester bond. Thus, PHBV is undeniably a polyester.

Next, we have Dacron (also known as PET) and Glyptal. Both of these are textbook examples of condensation polymers. They are synthesized by reacting a diol, specifically ethylene glycol, with dicarboxylic acids. Dacron uses terephthalic acid, while Glyptal uses phthalic acid. The reaction between the alcohol groups and the carboxylic acid groups naturally yields a long chain heavily populated with ester linkages. Therefore, both Dacron and Glyptal proudly wear the polyester badge.

Finally, we turn our attention to Novolac. Novolac is a linear resin produced through the condensation reaction of phenol and formaldehyde in the presence of an acid catalyst.

If we closely inspect the molecular architecture of Novolac, we see phenol rings linked together by methylene bridges ($-C{H}_2-$). There is absolutely no interaction between an alcohol and a carboxylic acid here, and consequently, no ester group is formed.

Because Novolac completely lacks the defining $-C(=O)-O-$ linkage, it cannot be classified as a polyester. It stands out as the correct answer to our question!