This question involves identifying the homopolymer formed from 4-hydroxybutanoic acid. A homopolymer is a polymer made from identical monomer units. 4-hydroxybutanoic acid has both a hydroxyl group (-OH) and a carboxylic acid group (-COOH), which can undergo condensation polymerization to form a polyester.

The polymerization occurs through an esterification reaction between the -OH and -COOH groups of different monomer molecules. The structure of 4-hydroxybutanoic acid is HO-CH₂-CH₂-CH₂-COOH. When it polymerizes, it forms polyester linkages: -O-CH₂-CH₂-CH₂-C(O)-O-.

Step 1: The monomer 4-hydroxybutanoic acid has the formula HO-(CH₂)₃-COOH.

Step 2: In condensation polymerization, the hydroxyl group of one monomer reacts with the carboxylic acid group of another monomer, eliminating water (H₂O).

Step 3: The repeating unit in the polymer is -O-(CH₂)₃-C(O)-, which corresponds to a polyester known as poly(4-hydroxybutanoate) or P4HB.

Step 4: Among the options, the correct structure is the one that shows this polyester linkage. The second option (with structure showing -O-CH₂-CH₂-CH₂-C(O)-O- as part of the chain) is correct.

Final Answer: The homopolymer is a polyester with the repeating unit $- O - {C H}_{2} - {C H}_{2} - {C H}_{2} - C (O) - O -$ .

Related Topics

Polymerization: The process of combining small molecules (monomers) to form a large molecule (polymer). Condensation polymerization involves the elimination of a small molecule like water.

Polyesters: Polymers containing ester functional groups in their main chain, often formed from dicarboxylic acids and diols or from hydroxy acids.

Formulae

General reaction for polyester formation from a hydroxy acid: $n H O - R - C O O H \to [- O - R - C (O) - O -] n + n H_{2} O$