A block copolymer of deuterated polystyrene (dPS) and 2-[2-(2-methoxyethoxy)ethoxyl ethyl methaerylate (PME3MA) spontaneously exposes the PME3MA, block, which is soluble in water, to the surface in a vacuum. dPS-PME3MA mixed with polystyrene (PS) segregates to the PS surface and changes the hydrophobic PS surface into hydrophilic surface. Neutron reflectivity, X-ray photoelectron spectroscopy, and dynamic secondary ion mass spectrometry probe the surface segregation of dPS-PME3MA to the surface of PS due to its PME3MA block. Sum-frequency generation vibrational spectroscopy detects exclusively the triethylene oxide (3EO) side chains of PME3MA regardless of a small fraction of dPS-PME3MA in the mixture, suggesting the conformation of the side chains influencing the segregation behavior. Because of the amphiphilic character of the methoxy-terminated 3EO side chains, the PME3MA block exposes the terminal methyl groups of the side chains to the surface to reduce the free energy of the system. However, such a hydrophobic methyl surface layer barely covers the EO part of the side chains; the surface quickly reconstructs and becomes hydrophilic upon contact with water. This is a technologically important demonstration of converting a hydrophobic polymer surface to a hydrophilic surface just by adding a small amount of block copolymer.