Metal-polymer studies

The metal-polymer studies were done in collaboration with C.A. Kovac, M.J. Goldberg, J.F. Morar and R.A. Poliak. The polymer-metal studies were done in collaboration with S.P. Kowalczyk. I wish to thank J. Stohr and A. Hitchcock for many enlightening discussions on NEXAFS techniques and interpretation and for timely access to their data throughout the course of these studies. Research was carried out in part at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences. 

The experimental evidence for the availability of the coordinative insufficiency of the transition metal ion in the propagation centers was obtained (175) in the study of the deactivation of the propagation centers by coordination inhibitors. On the introduction of such inhibitors as phosphine and carbon monoxide into the polymerization medium, the reaction stops, but the metal-polymer bond is retained. It shows that in this case the interaction of the inhibitor with the propagation center follows the scheme ... 

Olefin polymerization by catalysts based on transition metal halogenides is usually designated as coordinated anionic, after Natta (194). It is believed that the active metal-carbon bond in Ziegler-Natta catalysts is polarized following the type M+ - C. The polarization of the active metal-carbon bond should influence the route of its decomposition by some compounds ( polar-type inhibitors), e.g. by alcohols. When studying polymerization by Ziegler-Natta catalysts tritiated alcohols were used in many works to determine the number of metal-polymer bonds. However, as it was noted above (see Section IV), in two-component systems the polarization of the active bond cannot be judged by the results of the treatment of the system by alcohol, as the radioactivity of the polymer thus obtained results mainly from the decomposition of the aluminum-polymer bonds. 

The effect of ionic groups on the properties of bulk poly-mersilhas normally referred to studies on polyelectrolytes in which an ionic group is covalently attached to the polymer chain which is usually neutralized by a metallic counterion. Studies of systems consisting of neutral polymers with dissolved inorganic salts are only beginning to receive considerable attention. 

Typically, the first three effects, which deal with metal-polymer and metal-inhibitor interactions, are studied with respect to corrosion control processes. In this paper, we have also examined the relationship between the inhibitor compounds and the polymeric top coat from both a chemical and a physical point of view. 

Various transition metal catalysts, including those based on Rh, Pt, Pd, Co, and Ti, have been bound to polymer supports—mainly through the phosphenation reaction described by Eq. 9-65 for polystyrene but also including other polymers, such as silica and cellulose, and also through other reactions (e.g., alkylation of titanocene by chloromethylated polystyrene). Transition-metal polymer catalysts have been studied in hydrogenation, hydroformylation, and hydrosilation reactions [Chauvin et al., 1977 Mathur et al., 1980]. 

Carlise JR, Week M. Side-chain functionalized polymers containing bipyridine coordination sites polymerization and metal-coordination studies. J Pol3mi Sci Part A Polym Chem 2004 42 2973-2984. 

Finally, Majda has investigated a novel inorganic membrane-modified electrode [32]. The membrane used was a microporous alumina prepared by anodizing metallic aluminum in an acidic electrolyte [33]. Majda et al. lined the pores of these membranes with polymers and self-assembled monolayers and studied electron and ion transfer down the modified pore walls to a substrate electrode surface [32]. Martin and his coworkers have used the pores in such membranes as templates to prepare nanoscopic metal, polymer, and semiconductor particles [34],... 

Examples. Combined experimental—theoretical studies lead to information at a level not easily obtainable from either approach separately15. Several detailed examples are provided in chapter 7 to illustrate this point, and to provide the basis for the conclusions drawn on relevant polymer surfaces and the early stages of metal-polymer interface formation. This portion of the book is for the reader who wants to become familiar with details upon which certain conclusions, in the final chapter, have been drawn. 

The experimental spectroscopic methods discussed below are performed in the steady state, i.e., the time average of the nuclei positions is fixed. This justifies the use of the time-independent Schrodinger equation in the calculations. Dynamical systems are also of some interest in the context of metal-polymer interfaces in studies of, for instance, the growth process of the metallic overlayer. Also, in the context of polymer or molecular electronic devices, the dynamics of electron transport, or transport of coupled electron-phonon quasi-particles (polarons) is of fundamental interest for the performance... 

The degree of ionicity in the bond between a metal atom and a polymer, or molecule, is related to the ionization potential and electron affinities of the substituents. The metals we have studied are of interest as electron injecting contacts in electronic devices. These metals must have a low ionization potential (or work function), of the same order as the electron affinity of the polymer, in order for the charge transfer process to occur. If the ionization potential of the metal is lower than the polymery-electron affinity, spontaneous charge transfer occurs which is the signature of an ionic bond. Thus, the character of the charge distribution in the metal-polymer complexes we are studying is related to the situation in the electronic device. 

The application we have in mind for the metal-polymer interfaces discussed in this book is primarily that where the polymer serves as the electroactive material (semiconductor) in an electronic device and the metal is the electric contact to the device. Metal-semiconductor interfaces, in general, have been the subject of intensive studies since the pioneering work of Schottky, Stromer and Waibel1, who were the first to explain the mechanisms behind the rectifying behaviour in this type of asymmetric electric contact. Today, there still occur developments in the understanding of the basic physics of the barrier formation at the interface, and a complete understanding of all the factors that determine the height of the (Schottky) barrier is still ahead of us2. 

The highly crosslinked, three-dimensional network structure of the Cr(III) coordination polymer is considerably more stable at elevated temperatures than the Zn(II) polymer or the other transition metal polymers which have been studied. For example, while the Cr(III) sample sustains a loss in weight of about 30% at 850°C., the Zn(II) coordination polymer loses 60% under similar conditions. 

The application of photoelectron spectroscopy (PES) for the investigation of polymer-metal interfaces is discussed in this chapter. The information obtainable from both core-level spectra and valence-band spectra is briefly described. The approach of model compounds to study specific interactions is shown to be a useful aid to the understanding of polymer-metal reactivity. Emphasis is given to a number of experimental aspects relevant to polymer-metal interface studies, such as sample preparation and problems such as beam induced dam ge. 

Most of the illustrative examples will come from polyimide-metal interface studies directed at investigating the role of interfacial chemistry in adhesion at these interfaces and the non-equivalence of polymer-on-metal and metal-on-polymer interfaces. 

Photoelectron spectroscopy (PES) has become an important and widely used tool in material science (1-3). It has been a particularly fruitful technique for the investigation of polymers (4-9). In this review, we will focus on the application of photoelectron spectroscopy to the investigation of the interfaces between metals and polymers. These studies are directed primarily to understand the role of Interfacial chemistry in the adhesion between metals and polymers. Two aspects, which will be emphasized here, are the experimental approaches in PES studies of polymer/metal interfaces and the types of information accessible from the PES experiments. The experimental emphasis will be on preparation of appropriate samples for polymer/metal interface studies, practical problems... 

Ion beams are often utilized to prepare clean surfaces for PES studies or for depth profiling through a sample. This causes problems in polymer studies as the surface can be chemically degraded as has been demonstrated in the case of polyimide (19,20). This effect, however, has been used to increase metal/polymer adhesion, while the exact mechanism (chemical, mechanical) for the improved adhesion for the metals to polyimide is not yet completely understood (21,22). 

Core-level spectra of the metal generally have been little utilized in polymer/metal interface studies. Metal core levels are often much broader than the C Is, 0 Is, or... 

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