3D printed nanocomposites using polymer grafted graphene oxide prepared by multicomponent Passerini reaction

In order to generate 3D printed nanocomposites, good compatibility between the polymer resin and the nanoparticle is necessary. This is often achieved by modifying the surface of the nanoparticle such as the here employed graphene oxide (GO). In this work, we have explored the use of the multicomponent Passerini reaction to graft poly(N-isopropyl acrylamide) (PNIPAM) to and from the surface of GO in order to increase the dispersibility of GO in the triethylene glycol dimethacrylate (TEGDMA) and bisphenol A-glycidyl methacrylate (Bis-GMA) resin. For the grafting to process, aldehyde-terminated PNIPAM was prepared by RAFT polymerization. The polymers of various lengths - PNIPAM(80), PNIPAM(120), and PNIPAM(228) - were grafted onto commercial GO, which was used as received, simply by stirring the aqueous solution at ambient temperature in the presence of cyclohexyl isocyanide. The grafting density was found to decrease with increasing molecular weight from 0.61 to 0.12 polymers per nm(2). The grafting from procedure entailed the immobilization of RAFT agents by Passerini reaction on the surface of GO, followed by RAFT polymerization of NIPAM. Analysis of the resulting polymer grafted GO by thermogravimetric analysis (TGA) suggests that the growth of the polymer on the surface slowed down. The various PNIPAM grafted GO was mixed with the resin and 3D printed using a three-component visible light initiator. The 3D printed strips were analyzed by three-point bending test revealing an improvement in flexural modulus of 60-70% at 0.10 wt% modified GO. In contrast, the flexural modulus of the resin containing unmodified GO decreased noticeable.