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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. [3] The resulting shrinkage stress generated during the curing of the material may result in marginal leakage between the restoration and the tooth. As a consequence, marginal staining, postoperative sensitivity, or the formation of secondary caries can arise.2,2-Bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (bis-GMA) and bis-[(2-methacryloyloxyethoxy-carbonyl)-amino]-2,2,4-trimethylhexane (UDMA) are the most frequently used crosslinking monomers in dental composites. These monomers are highly reactive in free-radical polymerization, exhibit a relatively low polymerization shrinkage, and enable the formation of polymer networks with excellent mechanical Polymerization shrinkage of dental composites remains a major concern. Free-radically polymerizable cyclic monomers can be a conceivable alternative to methacrylates for the development of low-shrinkage composites. In this study, the one-step synthesis of the novel low viscosity difunctional vinylcyclopropanes 1-4 is described. Photopolymerization kinetics of these monomers are investigated by photo-differential scanning calorimeter, using bis(4methoxybenzoyl)diethylgermane as photoinitiator. Real-time near-infrared photorheology measurements are performed to evaluate rheological behavior (i.e., time of gelation, polymerization-induced shrinkage force) and chemical conversion (i.e., double bond conversion at the gel point, final double bond conversion) of the vinylcyclopropanes in situ. The potential of these monomers as reactive diluents in dental restorative materials is evaluated. Composites based on vinycyclopropanes 1-4 show good mechanical properties and exhibit significantly lower volumetric shrinkage and shrinkage stress than corresponding dimethacrylate-based materials. The results indicate that such monomers are promising candidates for the replacement of commonly used low viscosity dimethacrylates such as triethylene glycol dimethacrylate in dental composites.

Dispersion of carbon nanotubes and carbon nanofibers is a crucial processing step in the production of polymer-based nanocomposites and poses a great challenge due to the tendency of nanofillers to agglomerate. One of the most effective methods for dispersion is the use of a three-roll mill, which is a well-established method and results in agglomerates below 5 µm. Nevertheless, this process is time-consuming and thus a limiting factor for industrial applications. Our aim was to establish an easy and efficient ultrasonic dispersion process, characterize the dispersion parameters, and compare both methods, ultrasonication and the three-roll mill. We applied rheological tests and analyzed the agglomerate sizes by an image fit of the microscopy images. All these analyses combined deliver a valuable set of information about the dispersion’s quality and, therefore, allows the improvement and further adaptation of the dispersion process.