[Zurück]

Y. Catel, P. Fässler, U. Fischer, C. Gorsche, S. Schörpf, S. Tauscher, R. Liska, N. Moszner:
"Evaluation of Difunctional Vinylcyclopropanes as Reactive Diluents for the Development of Low-Shrinkage Composites";
Poster: EPF 2017, European Polymer Congress, Lyon; 02.07.2017 - 07.07.2017; in: "16th EPF European Polymer Congress", (2017), S. 57.

Composites are commonly used dental restorative materials which present excellent aesthetic properties.[1] They are made up of an organic matrix and silanized inorganic fillers. The organic matrix typically contains a mixture of different dimethacrylates and additives (photoinitiator system, stabilizer, etc.). Polymerization shrinkage is one of the main drawbacks associated with the use of dental composites.[2] The resulting shrinkage stress generated during the curing of the material may result in marginal leakage between the restoration and the tooth. It has been reported that ring-opening polymerization of cyclic monomers leads to a significant reduction of the shrinkage compared to conventional methacrylates.[3] Among these cyclic monomers, 1,1-disubstituted 2-vinylcyclopropanes (VCPs) were found to be particularly interesting.[4] Indeed, contrary to the other ring-opening monomers, VCPs are stable in the presence of humidity and acidic/basic impurities, which is essential for dental applications. We recently reported that bis(4-methoxybenzoyl)diethylgermane (BMDG) is an excellent initiator for the photopolymerization of VCPs.[5] The use of BMDG as photoinitiator instead of camphorquinone (CQ) / ethyl 4-(dimethylamino)benzoate (EDAB) led to a significant increase of the VCP polymerization rate, enabling for the first time the development of VCP-based low-shrinkage composites. The organic matrix of these composites was based on a mixture of a crosslinking VCP bearing amide groups and of various monofunctional VCPs as reactive diluents. Monofunctional monomers are not ideal as diluent because unreacted monomer can easily be leached out of the polymer network. Low-viscous crosslinking VCPs would therefore be great candidates as diluent monomers for low-shrinkage composites. In this context, we took an interest in the preparation of monomers 1-4.

VCPs 1-4 were successfully synthesized in good yields. Photopolymerization of these monomers was investigated using photo-DSC. VCPs 1-4 are more reactive than triethylene glycol dimethacrylate (TEGDMA), a dimethacrylate which is frequently used in dental composites. RT-NIR-photorheology experiments further confirmed the high reactivity of VCPs 1-4 and enable a correlation between gelation, polymerization induced shrinkage stress and final conversion. All VCPs exhibit a significantly reduced shrinkage stress and good conversion. The final photopolymer networks of VCPs 1-4 show much more defined thermal polymer phase transitions and a lower storage modulus at ambient conditions. The possibility to use these monomers as reactive diluents in dental restorative materials was also evaluated. Composites based on VCPs 1-4 show good mechanical properties and exhibit significantly lower volumetric shrinkage and shrinkage stress than a corresponding dimethacrylate-based material. The results indicate that such monomers are promising candidates for the replacement of commonly used low-viscous dimethacrylates such as TEGDMA.

1. Moszner, N.; Hirt, T. J. Polym. Sci. Part A: Polym. Chem. 2012, 50, 4369.
2. Braga, R. R.; Ballester, R. Y.; Ferracane, J. L. Dent. Mater. 2005, 21, 962.
3. Takata, T.; Endo, T. Expanding monomers. Synthesis, Characterization, and Application, Sadhir, R. K. Ed., CRC Press, Boca Raton, FL, 1992.
4. Moszner, N.; Zeuner, F.; Völkel, T.; Rheinberger, V. Macromol. Chem. Phys. 1999, 200, 2173.
5. Catel, Y.; Fischer, U.; Fässler, P :; Moszner, N. Macromol. Chem. Phys. 2016, DOI: 10.1002/macp.201600463.

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