Much is known about the structure and order-disorder transitions of linear block copolymers.1-3 Detailed information about the kinds of microphase domain morphologies that can be found in block polymers, the composition of copolymer that display each structure, and the conditions for the transitions between these morphologies, as well as into a disordered state, is available. For graft polymers, there has been only one theoretical treatment

No abstract

No abstract

Diblock copolymers show a menagerie of morphologies1 as a function of the relative lengths of the blocks and the temperature (or the magnitude of x-N, where x is the Flory interaction parameter and N the degree of polymerization). These structures range from spheres to hexagonally ordered cylinders and lamellae, corresponding to decreasing mean curvature of the interphase boundary. More recently2 a three-dimensionally ordered structure called the ordered bicontinuous double diamond (OBDD) phase is found at styrene compositions 4>s between 0.62 and 0.66 for polystyrene-6-polyisoprene diblock copolymers. When a homopolymer is mixed with a diblock copolymer, the occurrence of macrophase separation adds a new dimension to the possible morphological variations that can be realized, and the phase diagrams of such blends exhibit fascinating complexities.3,4 Even when the amount of added homopolymer is below its solubility limits so that a single macroscopic phase is realized, a range of structure,

Colloidal solutions of monodispersed palladium in various size ranges from < l o 8, to 75 8, have been prepared by metal vapour synthesis, chemical reduction of Pd(OAc), or by reaction of Pd(dibenzylideneacetone)2 with hydrogen or CO, in the presence of stabilizing polymers. CO is adsorbed readily onto the surface of the colloidal particles. The infrared spectrum of the adsorbed CO is size dependent. The largest palladium colloid (75 8, by TEM), which contains well formed microcrystals, shows only bridging CO (1944 cm-I). The smallest colloid (10 8, by SAXS) shows only terminal CO (2037 cm-'), and the intermediate size colloids (18 and 23 8, by TEM) show both bridging and terminal CO. The populations of bridging and terminal CO adsorption sites can be altered by modification of the method of preparation or by subsequent addition of reagents which disrupt the polymer-metal interaction. The 75 MHz I3C NMR spectra of CO adsorbed on the palladium colloids are also size dependent. The smaller colloids (10 and 18 8,) exhibit broad lines ( w I l 2 = 12 and 20 ppm, respectively) centred near 190 ppm. The larger colloids, which contain metallic palladium as shown by TEM and XRD,show radically different behaviour. Under 3atm 13C0 only a free CO resonance is directly observed, which exhibits a temperature-dependent linewidth characteristic of chemical exchange. A spin-saturation transfer experiment establishes the presence of a second CO site in the system, in exchange with the free CO. The second species, assigned to CO adsorbed on microcrystalline palladium, has a mean chemical shift of 800 ppm in the case of the 75 A colloid and 700 ppm in the case of the 23 8, colloid.These experiments are designed to investigate the surface chemistry of colloidal transition metals in organic solvents by standard spectroscopic techniques, with a view to establishing a relationship between metallic clusters and mplecular clusters, and to determining the changes in chemical and physical properties which come about as cluster size increases from the molecular scale to the bulk.

No abstract

No abstract

No abstract