Addition Polymerization Mechanism

Steps:

• Identify monomer Z as an alkene with a C=C double bond suitable for addition.
• Recall that addition polymers form by breaking the double bond, linking monomers via free radical or chain reaction without eliminating small molecules.
• Determine the repeating unit: the opened alkene structure connected head-to-tail.
• Compare choices to find the linear chain with Z's modified unit.

Why D is correct:

• D depicts the repeating -[CH₂-CHZ]- unit, matching the addition polymerization definition where the double bond becomes a single bond in the chain.

Why the others are wrong:

• A shows ester linkages, typical of condensation polymers like polyesters.
• B has branched structure, not the linear chain from simple addition.
• C retains the double bond, which breaks in actual polymerization.

Final answer: D