Question

In a polymer recycling plant, polymer “X” was depolymerized by glycolysis in the presence of ethylene glycol and a suitable catalyst. The glycolysis reaction yielded the following compound (a bis-hydroxyethyl ester of terephthalic acid). Identify the polymer “X” from the following options:

• A. Poly(ethylene terephthalate)
• B. Polystyrene
• C. Acrylonitrile butadiene styrene
• D. Poly(vinyl chloride)

Hint:

In polymer recycling, glycolysis of PET always yields bis(2-hydroxyethyl) terephthalate (BHET). Recognizing this structure is key to identifying PET in exam questions.

Answer 1

The Correct Option is A

Step 1: Recall glycolysis of PET.
- Glycolysis is a chemical recycling method in which polyesters (like PET) are broken down in the presence of glycols (commonly ethylene glycol). - This depolymerization produces bis-hydroxyethyl terephthalate (BHET) as the main product.

Step 2: Analyze the given structure.
- The compound shown has: - A benzene ring with two ester linkages at para positions. - Each ester is connected to a \(-CH_2CH_2OH\) group. - This is the typical structure of bis(2-hydroxyethyl) terephthalate, i.e. BHET.

Step 3: Match with polymer precursors.
- PET (Polyethylene terephthalate) is synthesized by condensation of terephthalic acid (or dimethyl terephthalate) with ethylene glycol. - During glycolysis, PET is broken back into its monomeric unit BHET. - Thus, the observed compound clearly comes from PET.

Step 4: Eliminate incorrect options.
- (B) Polystyrene → contains styrene monomers (aromatic vinyl group), unrelated.
- (C) Acrylonitrile butadiene styrene → a copolymer, no terephthalate ester units.
- (D) Poly(vinyl chloride) → contains C–Cl bonds, no esters.
- (A) PET → contains terephthalate ester units, matches perfectly. Final Answer: \[ \boxed{\text{(A) Poly(ethylene terephthalate)}} \]