Synthesis of low-shrinkage polymerizable liquid-crystal monomers

Polymerization shrinkage remains a major barrier to the universal use of resin restorative in large posterior cavity preparations. A new bifunctional liquid crystal (LC) monomer, 2-(t-butyl), 1,4-bis-[4-(6-acryloxy-hexane-1-oxy)-benzoyloxy] benzene, with exceptionally low polymerization shrinkage, has recently been discovered. The purpose of this communication is to report a new, easy, high-yield synthetic route to synthesize this compound in comfortable larger batches. Synthetic and isolation details, chemical characteristics, and the polymerizable properties of a new structurally related by-product monomer, namely, 2-(t-butyl),1-[4-(6-acryloxy-hexane-1-oxy)-benzoyloxy], 4-[4-[6-(3-acryl oxy-propionoxy)-hexane-1-oxy]-benzoyloxy]-benzene, is also reported. The structural confirmation of this by-product indicates that it resulted from the Michael-type addition of acrylate ion on one of the terminal acryloxy groups of 2-(t-butyl), 1,4-bis-[4-(6-acryloxy-hexane-1-oxy)-benzoyloxy] benzene. The by-product itself, as well as the natural blend of the aforesaid both products as formed in the reaction mixture, also polymerized at room temperature with lesser volume shrinkage as compared to the conventional control (GTE) at similar degrees of conversion.