Which of the following molecules can be used as a monomer to generate a polyester polymer?

• A. ${\mathrm{CH}}_3\mathrm{OH}$
• B. ${\mathrm{HO}}_{2}C-R-{\mathrm{CO}}_{2}H$ (a dicarboxylic acid)
• C. $H_{2}O$
• D. ${\mathrm{CH}}_2={\mathrm{CH}}_2$

Answer: (B)

Verified step by step guidance

1. Understand that polyesters are formed by a condensation polymerization reaction between monomers containing both hydroxyl (-OH) and carboxylic acid (-COOH) functional groups, or between diols and dicarboxylic acids.
2. Identify the functional groups present in each given molecule: \( \mathrm{CH_3OH} \) is methanol (a monohydric alcohol), \( \mathrm{HO_2C-R-CO_2H} \) is a dicarboxylic acid, \( \mathrm{H_2O} \) is water, and \( \mathrm{CH_2=CH_2} \) is ethylene (an alkene).
3. Recognize that a suitable monomer for polyester formation must have at least two reactive sites (e.g., two -OH groups or two -COOH groups) to allow chain growth; a monohydric alcohol like methanol cannot form long polyester chains by itself.
4. Note that the dicarboxylic acid \( \mathrm{HO_2C-R-CO_2H} \) has two carboxylic acid groups, making it capable of reacting with diols (molecules with two -OH groups) to form polyester linkages through ester bonds.
5. Conclude that among the options, the dicarboxylic acid is the correct monomer type for generating polyester polymers, as it provides the necessary functional groups for condensation polymerization.