Laser-induced curing of functional polymers

Abstract

Abstraet-Telechelic oligomers and polymers have been cross-linked within milliseconds upon exposure to a UV laser beam in the presence of a photoinitiator. The polymerization reaction was followed in real-time by infrared spectroscopy and was shown to proceed with long kinetic chains (up to 20000 functional groups polymerized per initiating radical). Acrylate-functionalized polyesters proved to be the most reactive systems, with the formation of tightly cross-linked and strictly insoluble polymers. Their high sensitivity (0.1 mjcm^-2) makes these photoresists particularly well suited for laser direct imaging applications, with writing speeds up to 1000 ms^-1. The rate at which polymer chains grow in media undergoing cross-linking polymerization was determined from pulsed laser experiments. Similar results have been obtained with epoxy- and vinyl ether-functionalized polymers, which undergo a fast cationic polymerization in the presence of a photogenerated protonic acid. Interpenetrating polymer networks have been synthesized by laser irradiation of blends of acrylate- and epoxy-functionalized oligomers. These polymers combine the elastomeric character of cross-linked polyurethanes and the toughness of epoxy polymers. The two networks can be produced either simultaneously by irradiation at 325 nm (helium-cadmium laser), or one after the other upon two successive UV exposures, by acting on the wavelength of the laser emission and on the type of radical and cationic photoinitiators. These laser-sensitive polymers can be used as photoresists to produce microcircuits, as protective coatings of optical fibers, as recording media in holography, and as optical guides in photonic applications.