Montmorillonite (MMT) of which the surface was modified with a block copolymer with crosslinkable units was incorporated into methacrylate-based composites as nanofiller to improve dimensional and mechanical properties. A bifunctional block copolymer containing 2-isocyanato ethyl methacrylate in one block and poly(vinyl pyridine) units in the other block was prepared as the block copolymeric surface modifier for MMT through controlled/living radical polymerization technique. Application of the modified MMT in 2,2-bis[4-(2-hydroxy-3-methacryloyl-oxy)phenyl]propane (bis-GMA) based composites showed that polymerization shrinkages of the composites decreased as the content of modified MMT increased. Compressive and flexural strengths of the composites were also improved in the presence of the modified MMT, which demonstrate the beneficial effect of the modified MMT as a nanofiller and IEM as a cocrosslinkable unit. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012