A series of amphiphilic graft copolymers having a poly(allyl methacrylate) [poly(AMA)] backbone and polydimethylsiloxane (PDMS) side chains were studied by time of flight secondary ion mass spectroscopy (ToF-SIMS) in both hydrated and dehydrated states using cryogenic sample handling methods. Both the copolymers and the PDMS macromers used for grafting to the acrylate backone were synthesized using anionic methods, yielding copolymers with a tightly controlled molecular weight distribution and a tightly controlled PDMS graft chain length in a polymer brush surface configuration. The effects of hydration on surface chemical structure and graft length distribution at the surface were examined. Low mass ToF-SIMS studies provided direct structural evidence that the polymer surface reorganized between hydrated and dehydrated states. High mass ToF-SIMS (1000-5000 Da) studies detected oligomeric ion distributions of the PDMS macromer graft at both air and water exposed interfaces, but with a greatly decreased ion yield at the water exposed interface. This marks the first time that detection of high mass oligomeric ion distributions from water exposed (frozen) interfaces has been reported. The chain length distribution of PDMS at the surface was determined and no statistical difference in surface graft length distribution was detected between hydrated and dehydrated copolymers. The effects of polymer bulk structure and composition on graft length distribution at the surface were also examined. High mass ToF-SIMS (1000-5000 Da) results indicated that shorter chain lengths were more prominently represented in distribution of graft chains at the surface, regardless of polymer bulk structure, composition, or hydration condition. This is the first report of quantitative and high mass ToF-SIMS study of the effect of water absorption on polymer surface structure in both hydrated and dehydrated states, with control of the polymer structure and composition. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3224878]