SURFACE DEPLETION OF END-GROUPS IN AMINE-TERMINATED POLY(DIMETHYLSILOXANE)

The depletion of alkylamine terminal groups at the vacuum-polymer interface is measured for alpha,omega-difunctional poly(dimethylsiloxane) oligomers by X-ray photoelectron spectroscopy. The driving force for this depletion is the high relative surface energy of the amine terminal groups compared to that of the low surface energy poly(dimethylsiloxane) backbone. The degree of surface end group depletion, within the maximum sampling depth probed (ca. 7 nm), is found to be on the order of 40% for a 960 molecular weight oligomer and decreases slightly with an increase in the oligomer molecular weight. Angle-dependent measurements are applied to determine end-group concentration depth profiles. End-group depletion is largest at the shallowest sampling depths and decays rapidly toward the bulk. The decay profiles cannot be explained by simple monotonic decay functions, consistent with the expected effects of connectivity between the end groups and the chain backbone, but the data are insufficient to prove whether the profiles are oscillatory in nature, as expected from theoretical considerations.