Telechelic poly(ethylene glycol)-POSS amphiphiles at the air/water interface

Combining two non-surface-active building blocks, oligomeric poly(ethylene glycol) (PEG) and a completely hydrophobic polyhedral oligomeric silsesquioxane (POSS) cage, creates amphiphilic telechelic polymers (POSS-PEG-POSS), which exhibit surface activity at the air/water (A/W) interface. POSS moieties serve as the hydrophobic groups for hydrophilic PEG chains of different number-average molar mass (1, 2, 3.4, 8, and 10 kg mol(-1)). For short PEG chains (1, 2, and 3.4 kg mol(-1)), insoluble monolayers form, whereas POSS end groups were not sufficiently hydrophobic to keep higher molar mass hydrophilic PEG blocks (8 and 10 kg mol(-1)) at the A/W interface. Thermodynamic analyses of the 1, 2, and 3.4 kg mol(-1) POSS-PEG-POSS via surface pressure-area per monomer isotherms indicate that the POSS end groups reside at the A/W interface and that the PEG chains are squeezed into the subphase with increasing surface pressure. This conclusion is supported by X-ray reflectivity studies on Y-type Langmuir-Blodgett multilayer films which reveal a double-layer structure with a double-layer spacing of about 3.52 nm. These findings provide a strategy for producing new surface active species from non-surface-active precursors.