The surface composition of styrene polymers capped at one or both ends by perfluoro groups has been determined by ISS, XPS, and static SIMS. The homopolymers, with M n 29 000−59 000, have an excess of the perfluoro end groups at the surface that is inversely proportional to the chain length and is commensurate with one or both ends having perfluoro groups. In contrast, double perfluoro end capped homopolymers of M n ∼9000 have only one of the perfluoro groups at the surface. In blends of perfluoro end capped styrene with hydrogen-terminated styrene, the fluorinated end cap causes the former to segregate to the surface. Nevertheless, the extents of segment segregation of single and double perfluoro end capped polymers of weights 29 000−59 000 are similar. For blends of perfluoro-capped polymer with M n 9000 in styrene of M n 30 000, the molecular weight and perfluoro end caps both strongly influence the segment segregation. The concentration of fluorine at the surface of all the blends may be estimated from the homopolymer XPS data and the blend monomer composition determined by static SIMS.

End capping a polystyrene with perfluorooctyldimethylchlorosilane is shown to strongly influence the surface segregation in blends of deuterated and hydrogenous polystyrenes. The surface composition, determined by static secondary ion mass spectroscopy, of a low molecular weight blend containing 0.14 mole fraction deuterated polystyrene, end capped by proton donation from methanol, was only slightly increased compared to the bulk value, even after annealing for several days at 150 °C. A low molecular weight blend containing the fluoro-end-capped deuteropolymer showed immediate surface segregation, which increased to give ca. 60% deuterated polymer at the surface after annealing. A similar blend, but with the fluoro end cap on the hydrogenous polymer, exhibited a surface enrichment of 41% of the hydrogenous component.Annealing a high molecular weight blend of hydrogenous and deuterated polystyrenes at 155 °C resulted in the gradual segregation of the deuterated component to the surface. A blend of high molecular weight fluoro-end-capped deuterostyrene and hydrogenous styrene showed an increased rate of segregation under the same conditions.

The surface compositions of a series of random copolymers of styrene and deuteriostyrene have been determined by SIMS. The mechanism of fragmentation during the SIMS process is examined, and the contribution from naturally occurring isotopes is evaluated. The data are shown to fit a model of a completely random copolymer system if they are corrected for the effects of impurities introduced in the syntheses and for the contribution from 13C.

BSTRACT: Diblock and triblock copolymers of hydrogenous and deuterated styrene are synthesized to investigate chain-end segregation by static secondary ion mass spectroscopy. Films of the diblocks on silicon wafers show no significant chain-end segregation. In contrast, the triblocks show marked chain-end segregation on silicon wafers with or without the native oxide. Triblocks of isotopic structure D-H-D and H-D-H both showed end-group segregation, suggesting that the surface free energy differences between C-D and C-H are not the dominant factor.

Ultrasonic absorption has been measured in liquid n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-dodecane and n-tetradecane, over the temperature range from -40°C or the melting point to 25°C and frequency range 15 to 230 MHz. A relaxation observed in the four higher members of this series has been discussed in terms of rotational isomeric processes. The important feature of the results is that the frequency of the acoustically active conformation change decreases with increasing chain length. The variation is similar to that expected for the first normal mode of motion of a chain of damped torsional oscillators. The ratio of compressional to shear viscosities in these systems decreases with increasing chain length, again indicating that a rotational isomeric change of finite volume change is involved in both shear and compressional relaxation.