The method of neutron di raction and isotopic substitution (NDIS) with H/D substitution on both the solute and the solvent was used to determine the hydration structure of a methane molecule (CM 4 , M = H or D) in terms of partial pair correlation functions g HM (r) and g OM (r). Analysis of these two functions shows that a methane molecule is surrounded by a shell containing 19(2) water molecules, and provides direct experimental evidence that water molecules in the ® rst coordination shell of apolar molecules are tangentially orientated. There is generally good agreement between these observations and those obtained from the theoretical and computer-based model calculations. However, it is clear that the model calculations over-emphasize the longer range structure around the hydrophobic molecule.

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Present commercial rigid foams are based on polyester raw materials. It has now been demonstrated that certain hydroxyl-terminated polyethers can be used satisfactorily as a major component of rigid urethane foams. These polyethers are hexafunctional materials prepared by reacting propylene oxide with sorbitol.