Synthesis of low-shrinkage polymerizable methacrylate liquid-crystal monomers

As a part of the continuous pursuit to develop an ideal resinous dental restorative material for use in large posterior cavity restorations, this article reports the easy, high-yield synthesis and the incredibly low polymerization shrinkage property of a new bifunctional liquid crystal (LC) monomer. This new polymerizable nematic liquid crystal is the next higher homolog of the acrylate monomer reported in a previous work.1 It remains liquid crystalline between room and mouth temperatures and can be polymerized to isotropic polymer with the use of the same visible light inhibitor system as used with conventional monomers. The structure of this new monomer has been confirmed to be 2-(t-butyl), 1,4-bis-[4-(6-methacryloxy-hexan-1-oxy)-benzoyloxy]-benzene. Unlike the synthesis of its acrylate homolog, when the same procedure is adopted for the synthesis of this compound, the recovery of the product is not split by a sizable amount of the by-product. Therefore, the reaction is cleaner, with high yield and a less labor-intensive purification procedure. Thus, the synthetic methodology has the potential for easy commercial scale-up. The monomer (V) polymerizes at room temperature with a shrinkage of about 2 vol %, as compared to > 8 vol % for conventional control (GTE), at similar degrees of conversion.