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Linear viscoelastic dynamic rheological measurements were performed on symmetric diblock copolymers of deuterated polystyrene and poljKn-butyl methacrylate), denoted P(d-S-ó-nBMA). Isothermal frequency sweep data were time-temperature superposed. A transition from a disordered to ordered morphology was found with increasing temperature as a function of molecular weight. P(d-S-b-nBMA) with molecular weights less than 6.8 104 were always disordered, as evidenced by the scaling of the storage and loss moduli with frequency at low frequencies, G' = 2 and G' °= . Copolymers with molecular weights above 9.9 104 were always ordered, exhibiting very long relaxation times and appearing almost solidlike in the low-frequency limit. Mixtures of the 6.8 104 and 9.9 104 copolymers, however, showed a transition from fluid to solidlike behavior as the temperature was increased. This rheological data is consistent with the existence of a lower critical ordering temperature, LCOT, where a transition from a disordered to ordered state occurs with increasing temperature.

The high-temperature transition at 340 "C for the homopolymer of p-hydroxybenzoic acid (PHBA) has been shown to display characteristics typical of a plastic crystal or a highly ordered smectic phase transition.For low molecular weight samples of the homopolymer a nematic texture can be induced above this phase transition by modest external shear. However, for high molecular weight samples the material is intractable in this temperature regime. A much higher transition at 445 "C has been identified and characterized by DSC, TMA, and polarized light microscopy, indicating the presence of a nematic mesophase. Processing of the homopolymer above this transition results in fusion of the material.

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Perfl~toropolyethers (PFPEs) are widely used as lubricants on rnagrtetic recording media. The mobility of the PFPE on the protective carbon overcoat of the media is widely accepted to be intimately coupled to the resulting tribological performance. The flow properties of molecularly thin films of nonpolar PFPE Z and polar PFPE Zdol fractions on solid surfaces were investigated by measuring the spreading profiles. The spreading of Zdol exhibits terraced profiles with the formation of a molecular foot, a shoulder and a vertical step. To describe these features of Zdol spreading, we measured the Zdol thickness dependence of the surface energy, which is then used to calculate the thickness dependence of the disjoining pressure. The polar component of the Zdol surface energy exhibits oscillations as a futlction of PFPE thickness. The resulting oscillations in the disjoining pressure can be used to qualitatively describe the origins of terraced spreading. The characteristic Zdol spreading profile and surface energy oscillations of Zdol are attributed to molecular layering induced by polar interactior~s between the Zdol end-groups and the surface.