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Addition consumes the carbon–carbon double bond of vinyl chloride and retains chlorine as a side substituent. The interior repeat of A is thereforenamely polyvinyl chloride. Benzoyl peroxide supplies initiating free radicals; head-to-tail addition gives the usual backbone connectivity. End groups and tacticity are not uniquely specified by this repeat formula.

Polyvinyl chloride is the addition polymer of vinyl chloride, with repeat unit $-\mathrm{C}{\mathrm{H}}_2-\mathrm{CHCl}-$. Its covalently attached chlorine influences intermolecular interactions and processing behavior.

Rigid and flexible commercial forms can differ strongly because of additives and formulation. A material label therefore does not imply that every specimen has the properties of the additive-free polymer.

Vinyl chloride is chloroethene, $\mathrm{C}{\mathrm{H}}_2=\mathrm{CHCl}$. It is a small vinylic halide whose carbon-carbon double bond can participate in addition polymerization.

Polymerization converts many vinyl chloride molecules into polyvinyl chloride, with chlorine-bearing repeating units along the carbon backbone. The resulting polymer has physical properties very different from those of the molecular monomer.