Synthesis and characterization of the dental adhesive monomer 10-MDP

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发布于： 2023-05-12 16:45

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Author links open overlay panelPaula Roberta Perondi Furtado, Rafael Minski Savanhago, Nataly Castro, Rogerio Aparecido Gariani, Marcia Margarete Meier

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https://doi.org/10.1016/j.dental.2024.09.009 Get rights and content

Abstract

Many studies have demonstrated the excellent performance of 10-MDP (10-methacryloyloxydecyl dihydrogen phosphate) as a functional monomer for dental adhesive materials and as a primer for ceramic surfaces. Although adhesive performance is affected by the purity level of 10-MDP, this parameter is rarely described, and possible byproducts have been suggested in the literature, but have not been identified to date. The present study aims to present an accessible 10-MDP synthesis strategy with easily handled reagents and address the characterization challenges, especially in identifying byproducts. 10-MDP was synthesized from 10-hydroxydecyl methacrylate and phosphorus pentoxide in acetone. The final product was characterized by nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR) and mass spectrometry MALDITOF/TOF. The main chemical groups associated with 10-MDP were identified by ¹H, ³¹P, and ¹³C NMR analyses. Only mass spectrometry analyses (MALDITOF/TOF) could identify the presence of dimers as byproducts. Its proposed chemical structure indicates that the dimers were formed by the reaction between the phosphate ester groups and others formed by the reaction of the methacrylic group of 10-MDP molecules. Careful adjustment of the synthesis conditions to reduce the formation of these byproducts is also described. The results indicate that the characterization of 10-MDP batches as raw materials is an important task because, depending on the byproduct present, its ability to polymerize or acid etching capacity may be compromised.

Introduction

10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) is one of the most studied functional monomers in dental materials, especially in adhesives. Through the methacrylic group it can copolymerize with other monomers and through the phosphoric group, it can ionically interact with dental hydroxyapatite (HAp) [1], [2], [3], [4].

Many studies present the great performance of 10-MDP as a functional monomer in dental adhesive materials [5]. Additionally, in recent years, its performance as a zirconia ceramic primer has been described [6], [7]. Recently, Sánchez-Fernández et al. (2019) described the 10-MDP molecule as promising for the development of bone adhesive materials [8].

The self-assembly capability of 10-MDP in forming nano-layers was identified first to a synthetic hydroxyapatite surface [1], later to enamel and dentin surfaces [2] and validated using commercial MDP-containing adhesives applied to dentin [3], [4].

Molecular self- assembly, forming for example nanolayers, is based on the intermolecular physical interactions that allow the aggregation of molecules. Contaminants may interfere with this process by altering the expected performance of the dental adhesives.

Despite abundant literature demonstrating self-assembled nanolayer formation between 10-MDP and HAp [1], [2], [3], [4], in another study, this structure was sparsely observed when self-etching and universal dental adhesives containing 10-MDP were applied to human dentin [9]. To understand the effect of possible interferers on the behavior of 10-MDP, Zhao et al. (2021) revealed that both the solvent and pH affect the chemical interactions between 10-MDP and HAp [10].

In this way, Yoshihara et al. (2015) observed that the 10-MDP purity level obtained from different suppliers affects dentin adhesive performance. Through NMR spectroscopy, the authors observed the presence of impurities in commercial 10-MDP [11].

Kuraray patented the 10-MDP molecule in 1981 [12]. After the patents expired, the number of scientific publications increased. When using the descriptors: “(10-MDP or MDP or 10MDP) and dental” in the Scopus database it was identified that before 2005 an average of 3 articles/year were published and after, 19 articles/year were published. In recent years, the number of publications on this topic has increased significantly.

Despite this, it has been observed that most studies used 10-MDP supplied by industries such as Kuraray Noritake Dental Inc., Watson International Ltd [13], DM Healthcare Products [9], PCM, and DMI [11] and rarely described the 10-MDP purity level or synthesis strategies.

When analyzing the scientific articles that described the performance of 10-MDP in dental adhesives in detail, few authors synthesized it or presented characterization results. For example, the pKa values of different acid monomers have been determined, including 10-MDP synthesized by the authors following the Kuraray patent [14]. In another study, a homologous series of phosphate monomers, including 10-MDP, was synthesized [15]. In turn, Ogliari et al. (2008) described strategies for removing byproducts during methacryloyloxypentyl phosphate synthesis, exhibiting the FTIR and NMR spectra of the product obtained [16].

Therefore, considering the importance of further investigation of 10-MDP performance in dental and, more recently, in medical adhesives, and the information gap regarding the synthesis and purity level of this monomer, the present study aims to present an accessible 10-MDP synthesis strategy with easily handled reagents and addresses some characterization challenges, especially the identification of byproducts.

Section snippets

Reagents

1,10-pentanediol (Aldrich, USA), cyclohexane (Dinâmica), methacrylic acid (Dinâmica), p-toluenesulfonic acid (Aldrich, USA), 2,6-di-tert-butyl-4-methyl phenol (Aldrich), copper sulfate (Dinâmica), phosphorus pentoxide (Biotec), butylated hydroxytoluene (BHT, Aldrich, USA), molecular sieves (3 A), ethyl acetate, hexane, and acetone were supplied by Biotec and were used as received.

Synthesis and purification of 10-hydroxydecyl methacrylate (10-HDMA)

To synthesize the precursor of 10-MDP 1,10-pentanediol (15 mmol, 1.56 g), methacrylic acid (10 mmol, 4.3 g),

Synthesis and purification of 10-hydroxydecyl methacrylate (10-HDMA)

The first step was to react 1,10-decanediol and methacrylic acid in the presence of p-toluenesulfonic acid as a catalyst (Fig. 1) to obtain the precursor 10-HDMA.

Consequently, 10-HDMA (1), 10-DMA (decanedimethacrylate)(2), and water were obtained. From the total amount of product obtained, 73% refers to 10-HDMA, and 21% refers to 10-DMA, separated by column chromatography.

In the 10-HDMA FTIR spectrum (Fig. 2), the typical signs of C O (1717 cm⁻¹) and C C (1634 cm⁻¹) bond stretching are observed.

Synthesis and purification of 10-hydroxydecyl methacrylate (10-HDMA)

The first reaction, the synthesis of the precursor 10-HDMA, is called Fischer esterification, in which the carboxylic acid reacts with an alcohol to form an ester. To shift the equilibrium to the desired product, an excess of the dialkyl alcohol, 1,10-decanediol which reacts with methacrylic acid, was used and catalyzed by p-toluenesulfonic acid, as shown in Fig. 1.

In the chemical structure of 10-HDMA there are two distinct methylene groups attached to electronegative atoms, generating signals

Conclusion

NMR spectroscopy is a fundamental analysis for elucidating chemical structures, however, due to the similarity between the chemical structures of monomers and dimers, it presents some limitations to analyzed batches of 10-MDP. Thus, only mass spectrometry analyses (MALDITOF/TOF) could identify the presence of dimers as byproducts. The proposed chemical structures indicate that the dimers were formed by the reaction between the phosphate ester groups of 10-MDP and others formed by the reaction

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We are grateful to the National Council for Scientific and Technological Development (CNPq), the Santa Catarina Research Support Foundation (FAPESC), the Coordination for the Improvement of Higher Education Personnel (CAPES), and the Financier of Studies and Projects (FINEP). Furthermore, we would like to acknowledge the contribution of the mass spectra measurement from the Federal University of Santa Catarina.

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