Photopolymerization is best described as:

• A. A Process in Which Small Numbers Are Linked to Become a Chainlike Polymer Through a Photochemical Reaction with a Catalyst
• B. A Process that Uses Heat to Break Down Polymers
• C. A Process that Uses Mechanical Pressure to Polymerize
• D. A Process that Cures Polymers with Infrared Light

Answer: (A)

Photopolymerization relies on light to start the chemical reaction that links small units into a polymer chain. A photoinitiator absorbs photons and generates reactive species, such as free radicals, that initiate the growth of polymer chains by opening double bonds in monomers. This is a photochemical process driven by a catalyst (the initiator) and results in monomers joining to form long, chainlike polymers. That’s why this description fits best: small molecules are connected into a polymer through a light-activated reaction with a catalyst.

The other descriptions describe different processes: heat-driven breakdown of polymers is degradation, not building; using mechanical pressure suggests a pressure-driven or mechanochemical process, not typical photopolymerization; and curing with infrared light is not the standard way photopolymerization is initiated—infrared generally adds heat rather than starting the photochemical reaction, whereas UV or visible light is commonly used to activate the initiator.