Angle-resolved XPS of fluorinated and semi-fluorinated side-chain polymers

Angle-resolved XPS data (elemental quantification and high-energy-resolution C Is) are presented for ten polymers with side-chains of the form -OCO(CF(2))(y)F, -COO(CH(2))(2)OCO(CF(2))(y)F (y = 1, 2, 3) and -COO(CH(2)),(CF(2))(y)F (x = 1, y = 1, 2, 3; x = 2, y = 8). Particular attention was paid to charge compensation and speed of data acquisition, with co-addition from multiple fresh samples to give spectra with good energy resolution and good signal-to-noise ratio free from the effects of x-ray-induced degradation. Water contact angles for the polymers are also reported. The XPS data demonstrate preferential surface segregation of fluorine-containing groups for all but the shortest side-chain polymer, where the -OCOCF(3) side-chain either does not surface segregate or is too short for surface segregation to be detectable by angle-resolved XPS. In the other polymers studied the relative positions of functional groups in the side-chains correlate with the angle-resolved behaviour of the corresponding C Is components. This shows that the surface side-chains are oriented towards the polymer surface. For the -COO(CH(2))(2)OCO(CF(2))(y)F (y = 1) side-chain, the angle-resolved C Is data suggest reduced ordering and linearity compared with y = 2 and 3. For any particular series of polymers, e.g. -COO(CH(2))(x)(CF(2))(y)F, the water contact angles increase with y, consistent with burying of the hydrophilic ester groups as y increases. For any particular value of y the sequence of water contact angles is -COO(CH(2))(x)(CF(2))(y)F > -OCO(CF(2))(y)F similar to -COO(CH(2))(2)OCO(CF(2))(y)F, suggesting greater ordering and density of fluorocarbon species at the surface of the -COO(CH2),(CF2)yF side-chain polymers compared with the other polymers studied. For the -COO(CH(2))(2)(CF(2))(8)F polymer a water contact angle of 124degrees is measured, which is greater than that of poly(tetrafluoroethene). The -COO(CH(2))(2)OCO(CF(2))F polymer is unusual in that it shows a particularly low water contact angle (83degrees), suggesting that the probe fluid is able to sense both ester groups, consistent with the reduced ordering of the side-chain detected by angle-resolved XPS. Copyright (C) 2004 John Wiley Sons, Ltd.