Photopolymers

Photopolymers are polymers that undergo polymerization or cross-linking upon exposure to light, typically ultraviolet (UV) or visible wavelengths. They include acrylate- and epoxy-based resins, coatings, adhesives, hydrogels, and varnishes. A photoinitiator absorbs light and generates reactive species that start chain growth or cross-linking, enabling rapid curing at ambient temperatures.

The two main mechanisms are free-radical polymerization of acrylates and methacrylates initiated by Type I or Type II photoinitiators, and cationic polymerization of epoxies and vinyl ethers initiated by cationic photoinitiators. Light exposure provides spatial control, because the reaction proceeds only where illumination occurs; oxygen can inhibit radical polymerization at exposed surfaces.

Advantages include fast curing, room-temperature processing, and the possibility of solvent-free formulations, supporting high-resolution additive manufacturing and precision coatings. Limitations include shrinkage and internal stresses, surface inhibition by oxygen, limited depth of cure due to light attenuation, and brittleness or aging of the network.

Applications span stereolithography and digital light processing (DLP) in 3D printing, two-photon polymerization for microfabrication, dental and medical resins, protective coatings, photo-patternable electronics, holographic data storage, and microfluidic devices.

Environmental and safety considerations include residual monomer and photoinitiator toxicity, exposure to UV light, and disposal concerns. Ongoing research aims to develop more biocompatible, low-toxicity formulations, improve depth of cure, reduce shrinkage, and enable visible-light activation with advanced photoinitiators.