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

The depletion of alkylamine terminal groups at the vacuum-polymer inte rface is measured for alpha,omega-difunctional poly(dimethylsiloxane) oligomers by X-ray photoelectron spectroscopy. The driving force for t his depletion is the high relative surface energy of the amine termina l groups compared to that of the low surface energy poly(dimethylsilox ane) backbone. The degree of surface end group depletion, within the m aximum sampling depth probed (ca. 7 nm), is found to be on the order o f 40% for a 960 molecular weight oligomer and decreases slightly with an increase in the oligomer molecular weight. Angle-dependent measurem ents are applied to determine end-group concentration depth profiles. End-group depletion is largest at the shallowest sampling depths and d ecays rapidly toward the bulk. The decay profiles cannot be explained by simple monotonic decay functions, consistent with the expected effe cts of connectivity between the end groups and the chain backbone, but the data are insufficient to prove whether the profiles are oscillato ry in nature, as expected from theoretical considerations.