Monomer Identification in Addition Polymerization

Steps:

• Examine the repeat unit to identify the backbone and functional groups.
• Determine the polymerization type: addition, as no small molecules are lost.
• Locate where the double bond in the monomer would break to form the -CH2-CH2- links in the repeat unit.
• Compare choices to find the alkene that matches the unit exactly.

Why A is correct:

• Choice A is ethene (CH2=CH2), which undergoes addition polymerization to form the -[CH2-CH2]- repeat unit, per the mechanism where the pi bond opens.

Why the others are wrong:

• B is propene, producing a branched -[CH2-CH(CH3)]- unit, not matching the linear structure.
• C is a diene, leading to cross-linked polymers, unlike the simple chain shown.
• D is for condensation polymers like polyesters, requiring bifunctional monomers and losing water.

Final answer: A