Synthesis and FT-IR/Raman Characterization of a Graphene Oxide-Methacrylamide Monomer for Dental Applications

Abstract

Background: Graphene oxide (GO) is widely explored as a functional additive in polymer composites; however, its simple physical dispersion in dental resins often leads to poor interfacial stability and limited long-term performance. Covalent functionalization may overcome these limitations by enabling chemical integration into the polymer matrix. This study presents the synthesis and FT-IR/Raman characterization of GRAPHYMERE^®, a novel graphene oxide-based monomer obtained through exfoliation, amine functionalization with 1,6-hexanediamine, and transamidation with methyl methacrylate.

Methods: A novel GO-based monomer, GRAPHYMERE^®, was synthesized through a three-step process involving GO exfoliation, amine functionalization with 1,6-hexanediamine, and transamidation with methyl methacrylate to introduce polymerizable acrylic groups. The resulting product was characterized using FT-IR and Raman spectroscopy.

Results: Spectroscopic analyses confirmed the presence of aliphatic chains and amine functionalities on the GO surface. Although some expected signals were overlapped, the data suggest successful surface modification and partial insertion of methacrylamide groups. The process is straightforward, uses low-toxicity reagents, and avoids complex reaction steps.

Conclusions: GRAPHYMERE^® represents a chemically modified GO monomer potentially suitable for copolymerization within dental resin matrices. While its structural features support compatibility with radical polymerization systems, further studies are required to assess its mechanical performance and functional properties in dental resin applications.

Keywords: GRAPHYMERE; composite; dental materials; graphene; graphene oxide; polymer.

Figure 1

Reagents, intermediate product, and final product. (a) Molecular structure of the involved reagents: (1) Graphene oxide (GO), (2) 1,6-hexanediamine (ED), (3) methyl methacrylate (MMA); (b) Molecular structure of (4) graphene oxide functionalized with 1,6-hexanediamine (GO-ED); (c) (5) GRAPHYMERE^® supposed structure.

Figure 2

Functionalization of graphene oxide with 1,6-hexanediamine. The possible reaction for the insertion of 1,6-hexanediamine on GO is: (a) opening of an epoxide functional group; (b) nucleophilic substitution of a hydroxyl group; (c) transamidation of a carboxyl group.

Figure 3

Acrylic functionalization: reaction of transamidation of methyl methacrylate with the amine group of 1,6-hexanediamine functionalized GO. It consists of a two steps reaction: a reversible (double arrows) nucleophilic attack of the amine functional group bound to the GO on the carboxyl of the MMA, followed by an irreversible (single arrow) elimination of a methanol molecule.

Figure 4

Raman and IR spectra of GRAPHYMERE^® and pristine GO. (a) The Raman spectrum of GRAPHYMERE^® shows two prominent bands at 1301 and 1598 cm⁻¹, corresponding to the D and G bands typical of GO-based materials. (b) The IR spectrum of GRAPHYMERE^® displays absorption bands at 2929 and 2857 cm⁻¹, assignable to aliphatic C–H stretching vibrations, and a broad band in the region 1550–1650 cm⁻¹, consistent with N–H bending of amine groups. Bands related to GO functionalities (e.g., O–H and C=O stretching) may be overlapped by broader signals associated with methacrylamide moieties in the 3000–3400 cm⁻¹ region. (c) The IR spectrum of pristine GO reveals intense and broad absorptions associated with hydroxyl (O–H, ~3200–3400 cm⁻¹), carbonyl (C=O, ~1720 cm⁻¹), epoxy (C–O–C, ~1220–1260 cm⁻¹), and alkoxy (C–O, ~1050–1100 cm⁻¹) groups.

Figure 5

Examples of unsaturated functional groups capable of copolymerization with GRAPHYMERE^®. All molecules that have unsaturated bonds can copolymerize with GRAPHYMERE^® through a radical mechanism.