Materiali Polimerici Reticolati e Interpenetrati ottenuti per polimerizzazione sequenziale (Dual Curing) di oligomeri epossiacrilati modificati

The materials and methods used for the preparation of interpenetrated polymer network (IPN) by UV curing processes are reported. In particular, recent developments on the formation and characterization of some sequential IPN based on mixtures of commercially available diglycidyl ether of bisphenol-A (DGEBA) epoxy resins and UV curable epoxy-dimethacrylate resins are discussed. Finally, the photopolymerization kinetic behavior and thermal properties of some UV curable mixtures based on the modified epoxy-dimethacrylate resins for the preparation and characterization of a grafted sequential IPN are described. Interpenetrated Polymer Networks (IPN) are often used to describe a combination of at least two polymers forming two distinct networks, where at least one polymer is polymerized or crosslinked in the immediate presence of the other. In an IPN, each polymer is crosslinked to itself, but not to the other, so two polymer networks are interpenetrated each to other. These highly crosslinked polymer materials can be achieved by using thermosetting multifunctional oligomers, such as epoxy, polyurethanic and acrylic commercially available resins. Recently, our contribution in this research field has exploited the second approach in which a commercially available diglycidyl ether of dimethacrylate bisphenol-A (DGEBA) epoxy resin (commonly called vinylester or epoxy-dimethacrylate resin: EPDMA) were modified with phtalic anhydride to prepare a grafted seq-IPN. A ring opening reaction of PA anhydride was promoted by hydroxyl groups on EPDMA chains by using 4- dimethylaminopyridine (DMAP) as catalyst. The modified EPDMA resins provides a novel approach for preparing grafted seq-IPN by using commercially available DGEBA epoxy and modified EPDMA resins. The obtained results suggest that the modified EPDMA resins can represent a convenient method to reduce the phase separation after curing providing a fine control of the final mechanical and optical properties. Besides, the temperature for the thermal curing in a grafted seq-IPN can be conveniently lowered at 90 °C. Finally, the preparation of grafted-seq-IPN can be easily obtained by firstly UV curing of methacrylate groups in modified EPDMA resins and then applying a thermal treatment to crosslink epoxy groups in a temperature range between 90° and 105°C. This curing sequence allows reaching quite high Tg values and good conversion degrees both for UV and thermal curing treatments.