Desenvolvimento de lentes oftálmicas por fotopolimerização de compostos orgânicos.

Abstract

Industrial, technological and scientific considerations are responsible for the prominence being gained by photo polymerization processes as substitutes of conventional organic peroxide thermally initated processes for the development of ophthalmological lenses. The latter, have long curing cycles (up to 20 hours) while the polymerization reaction in photo initiated processes is very fast, with cycles being completed within 5 minutes, generating a tremendous reduction in energy and time. In the present work the materials, the UV cure (photo polymerization) reaction and the ophthalmic lenses produced by photo polymerization were characterized. The main goal was to reduce the cure time, the energy consumption and to improve the quality of the ophthalmic lenses produced. Monomers, photo initiators and lenses were characterized by analytical techniques which included: thermogravimetry (TG), differential scanning calorimetry (DSC), infra-red spectroscopy (FTIR) and vibrational spectroscopy on the ultra-violet visible region (UV-Vis). The lenses produced were visually inspected and their optical (refractive index and UV-A transmittance) and mechanical (hardness) properties were determined. Thermogravimetric results confirmed the low thermal stability of the reagents which showed the following decreasing order of thermal stability for the monomers RAV-700® >SR-355® >SR-339® and photo initiators CHIVACURE DBK® >IRGACURE 2022® >DAROCUR 1173®. The calorimetric behavior of the reagents was dominated by endothermic events associated with volatilization of SR-355®, CHIVACURE DBK®, DAROCUR 1173® e IRGACURE 2022® and decomposition of SR-355®, RAV-700® e IRGACURE 2022® and fusion of CHIVACURE DBK®. Only SR-355® showed exothermic events associated with polymerization and decomposition. The lenses produced were thermally stable up to 1460C. FTIR spectra confirmed the structure of the reagents employed, displaying methyl, vinyl, carbonyl and other characteristic bands. The lenses obtained from mixtures M6 and M7 displayed properties (hardness and refractive index) deemed adequate for ophthalmic use.