Light-induced crosslinking polymerization

Light‐induced polymerization of multifunctional monomers is a powerful method to transform a liquid resin into a solid polymer almost instantly, selectively in the illuminated areas. The reaction can conveniently be followed by real‐time infrared spectroscopy, a technique which records directly conversion versus time curves in photosensitive resins undergoing ultrafast curing upon UV or laser exposure. The photoinitiator was shown to play a key role in laser‐induced polymerization because of the monochromatic character of the emitted radiation. By using highly sensitive acrylate photoresists, relief images of micronic size were obtained by fast scanning with a focused laser beam. The laser direct imaging technology makes image transfer obsolete and eliminates the manufacture of photolithographic masks. Polymer networks of different architectures have been obtained by UV irradiation of various monomer blends: acrylate–epoxide, acrylate–vinyl ether, acrylate–polyene, vinyl ether–maleate and thiol–polyene. With monomers polymerizing by different mechanisms, ie radical and cationic types, interpenetrating polymer networks have been generated upon UV exposure in the presence of adequate photoinitiators. The crosslinking reaction was also performed in the solid state on polybutadiene which was plasticized with a multifunctional acrylate or thiol monomer. Thermoplastic elastomers were transformed within a fraction of a second into an insoluble material showing a greatly improved resistance to heat and chemicals, because of the tight polymer network formed. © 2002 Society of Chemical Industry