fotopolymerisation

Fotopolymerisation, also spelled photopolymerisation, is a light-induced polymerisation process in which monomers or oligomers with unsaturated groups form a crosslinked polymer network upon exposure to light, typically ultraviolet or visible light. It is widely used because it allows spatial and temporal control of curing at ambient temperature.

Mechanism and chemistries: There are two main pathways: radical photopolymerisation and cationic photopolymerisation. In radical photopolymerisation, a photoinitiator absorbs light to generate free radicals (for example, camphorquinone with amines), which initiate chain growth in acrylates or methacrylates. In cationic photopolymerisation, onium salts generate Lewis acids that start epoxy or vinyl ether polymerisation. Oxygen can quench radicals, inhibiting surface cure; this inhibition can be mitigated by inert atmospheres or specific formulations. Depth of cure depends on resin formulation, light intensity, and exposure time.

Materials and processing: Typical resins include acrylates, methacrylates, and epoxy acrylates. Photoinitiators vary by system, with visible-light cures often using acylphosphine oxides or related compounds, sometimes paired with co-initiators and sensitizers for LED compatibility. Processing involves coating or printing a liquid resin and exposing it to light to trigger curing; in 3D printing, technologies such as stereolithography (SLA) and digital light processing (DLP) rely on photopolymerisation principles.

Applications and considerations: Photopolymerisation is used in additive manufacturing, dental resins, coatings and inks, photolithography for microfabrication, and adhesive formulations. Advantages include rapid curing, room-temperature processing, and precise spatial control. Limitations include polymerisation shrinkage and potential brittleness, sensitivity to oxygen, depth limitations, and the cost or toxicity of certain photoinitiators.