Diol dimethacrylates (DD) that possess long aliphatic chains were incorporated into the conventional dental resin mixtures (e.g., BIS-GMA and TEGDMA) in order to reduce the polymerization stress and shrinkage of final copolymers. It was found that the polymerization shrinkage of the standard copolymer (60 mol % BIS-GMA and 40 mol % TEGDMA) could be reduced even by 20% when TEGDMA is substituted by a long aliphatic diol dimethacrylate. These phenomena can be attributed to the low miscibility of BIS-GMA and DD, which causes long aliphatic chains of DD to remain in coil form in a reaction mixture. The coils can be unwound and expand as a result of the formation of covalent bonds during polymerization and thus reduce the polymerization shrinkage.