Highly ordered, hydrothermally stable, caged cubic mesoporous silica structures (Im 3m) with unusually large pore size (120 Å) have been synthesized by using hydrophobic poly(butylene oxide) containing triblock PEO-PBO-PEO copolymer as a structure-directing agent.Ordered large pore materials are in great demand because of their potential applications for catalysis, separation of large molecules, medical implants, semiconductors, magnetoelectric devices, etc. [1][2][3][4][5][6][7][8] Using triblock poly(ethylene oxide)-poly-(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) copolymers as structure-directing agents, we have previously reported the synthesis of highly ordered hexagonal mesoporous silica structures (SBA-15) with large pore sizes of 50-300 Å. 2 Three-dimensional cubic mesoporous structures, such as MCM-48 (Ia 3d), 1 SBA-1 (Pm 3n) 7 and SBA-16 (Im 3m), 2 show advantages compared to hexagonal mesoporous structures with one-dimensional channels. However, such cubic structures could be synthesized only under strict conditions. Calcined SBA-16 synthesized with PEO-PPO-PEO triblock copolymers has the largest pore size (54 Å) among these cubic silica structures, but can only be synthesized with large PEO segment amphiphilic PEO-PPO-PEO block copolymers, such as F127 (EO 106 PO 70 EO 106 ) in a narrow range of reaction compositions at room temperature. 2b The small differences of hydrophilicity/ hydrophobicity between PEO and PPO chains at room temperature might be one of the reasons leading to such a small pore size.Here, we report the synthesis of a highly ordered, ultra hydrothermally stable caged cubic mesoporous silica structure (FDU-1, Im 3m) with large, uniform pore size (120 Å) by using the more hydrophobic poly(butylene oxide) containing triblock copolymer PEO-PBO-PEO as the structure-directing agent.Cubic mesoporous silica FDU-1 samples were synthesized by using the triblock copolymer EO 39 BO 47 EO 39 [B50-6600 (Dow) M n = 6800] as the structure-directing agent under acidic conditions. In a typical experiment, 0.5 g of B50-6600 was dissolved in 30 g of 2 M HCl. To this homogeneous solution, 2.08 g (0.01 mol) of tetraethylorthosilicate (TEOS) was added with vigorous stirring for 24 h. The resulting solid was then aged at 100 °C for a further 24 h. The solid product was filtered off, washed, and dried in vacuo at room temperature. Calcination was carried out in an oven at 550 °C for 6 h in air.Small angle X-ray diffraction (XRD) patterns of as-synthesized and calcined FDU-1 are shown in Fig. 1. As-synthesized FDU-1 shows a well resolved XRD pattern and the first diffraction peak appears at a low angle (2q = 0.68). After calcination the first diffraction peak is shifted slightly (2q = 0.73) due to shrinkage. Calcined FDU-1 shows nine well resolved Bragg peaks. Combined with TEM analysis (see below) we can index the diffraction peaks to 110, 200, 211, 220, 310, 222, 400, 411 and 420 reflections for space group Im 3m (Q 229 ), respectively. The relative intensity of these observed peaks follows the...