Photopolymerisation

Photopolymerisation is a light-driven form of polymerisation in which a liquid or prepolymer resin containing photoinitiators is exposed to light to initiate polymer chain growth. The reaction converts low-molecular-weight monomers into a crosslinked polymer network, often at ambient temperature and with rapid curing.

Most common is free-radical polymerisation of acrylate and methacrylate monomers. Upon irradiation, photoinitiators absorb photons and generate reactive species. Type I initiators cleave to form radicals directly, while Type II systems require a co-initiator (such as an amine) to generate radicals through electron transfer. These radicals initiate chain growth, propagate, and, with multifunctional monomers, produce crosslinking. In cationic photopolymerisation, photoinitiators or onium salts generate strong acids that open ring structures (for example epoxides), leading to chain growth.

Light sources used include UV lamps, LEDs, and, with suitable initiators, visible-light systems. The wavelength range is chosen to match the photoinitiator’s absorption, enabling selective initiation and spatial control.

Applications span stereolithography and digital light processing in additive manufacturing, dental resin composites, coatings and adhesives, holographic data storage, and microfabrication. Photopolymer systems offer rapid, room-temperature curing with good spatial resolution, but face challenges such as oxygen inhibition in radical systems, shrinkage and internal stress, limited penetration depth of light, potential toxicity or coloration from initiators, and the need for careful formulation to balance reactivity and stability.