Which polymerization releases a small molecule during the reaction?

• A. Addition polymerization
• B. Condensation polymerization
• C. Polymerization by expansion
• D. Hydrolysis polymerization

Answer: (B)

Condensation polymerization is the process where joining monomers results in the loss of a small molecule, such as water or methanol, with each linkage formed. This byproduct release is the hallmark of condensation; the polymer grows as monomers condense and eject a tiny molecule.

In contrast, addition polymerization builds the chain by adding monomers across a double bond or reactive site without producing a byproduct, so no small molecule is expelled. The other terms listed aren’t standard mechanisms for forming polymers with byproducts in the way condensation polymerization does, and they don’t fit the idea of releasing a small molecule during the reaction.