Hybrid nanocomposites prepared by in situ photopolymerization using photoinitiator-modified montmorillonite

Abstract

Abstract A series of hybrid nanocomposite coatings were prepared by UV curing of the urethane dimethacrylate monomers with various amounts of photoinitiator-modified montmorillonite (1, 3 and 5 wt.%, respectively). First, two different types of free-radical generating photoinitiators, a Type I – Irgacure 2959 (alpha cleavage type) and a Type II – benzophenone derivative (hydrogen abstraction type) were synthesized and bounded on Cloisite Na + layers. The homogeneous thin films were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis spectrophotometry, thermogravimetric analysis (TGA) and mechanical testing. The XRD pattern of organic/MMT nanocomposite with 3 wt.% PI-1-MMT (Type I) hybrid photoinitiator displays a small peak at 6.36° (1.39 nm) characteristic to an intercalated structure, while in the XRD diffraction spectra of polymeric nanocomposites with PI-2-MMT (Type II) photoinitiator, no diffraction peaks were visible, suggesting the formation of an exfoliated structure. These outcomes were further confirmed by TEM and UV analyses, and can be attributed to the binding pathways (grafting/intercalation) of the photoinitiator molecules on the nanoclay surface. Also, the in situ photogeneration of silver nanoparticles (5 ÷ 10 nm diameter) triggered by photoinitiator-MMT systems was proved, when small well dispersed Ag NPs were formed.