Polymethyl methacrylate , metallic

Another differential reaction is copolymerization. An equi-molar mixture of styrene and methyl methacrylate gives copolymers of different composition depending on the initiator. The radical chains started by benzoyl peroxide are 51 % polystyrene, the cationic chains from stannic chloride or boron trifluoride etherate are 100% polystyrene, and the anionic chains from sodium or potassium are more than 99 % polymethyl methacrylate.444 The radicals attack either monomer indiscriminately, the carbanions prefer methyl methacrylate and the carbonium ions prefer styrene. As can be seen from the data of Table XIV, the reactivity of a radical varies considerably with its structure, and it is worth considering whether this variability would be enough to make a radical derived from sodium or potassium give 99 % polymethyl methacrylate.446 If so, the alkali metal intitiated polymerization would not need to be a carbanionic chain reaction. However, the polymer initiated by triphenylmethyl sodium is also about 99% polymethyl methacrylate, whereas tert-butyl peroxide and >-chlorobenzoyl peroxide give 49 to 51 % styrene in the initial polymer.445... 

In investigating how Cooper pairs56 in a superconductor (Pb) may retain their coherence if they penetrated, across a thin tunneling gap (a film of polymethyl methacrylate, PMMA) into a conventional nonsuperconducting metal (Al), Jaklevic57 and Lambe58 discovered accidentally in 1966 that steps in the current, when displayed as the second derivative dzI/dVz versus V, were actually due to vibrations in polar molecules (IR) and also vibrations in... 

We briefly describe here the results obtained from studies of copper, nickel and chromium overlayers deposited on polystyrene, polyvinyl alcohol, polyvinyl methyl ether, polyethylene oxide, polyvinyl acetate and polymethyl methacrylate. Using X-ray photoemission spectroscopy we measured significant variations in the core binding energies and lineshapes as we varied both the metal and the substrate atoms. These changes can be related to both differences between the intrinsic properties of the metal atoms as well as to differences in the interactions with the substrates. In the following sections we describe the details of... 

The interfaces formed by evaporating copper, nickel and chromium layers on polystyrene, polyvinyl alcohol, polyethylene oxide, polyvinyl methyl ether, polyvinyl acetate and polymethyl methacrylate have been studied with X-ray photoemission spectroscopy (XPS). At submonolayer coverages of the metals, the peak positions and widths of the metallic electron core levels vary significantly from one polymer substrate to another. Most of... 

A few polymers can be converted back to their monomers for purification and repolymerization. Polymers formed by ring-opening polymerization fall in this class, as shown in the foregoing by the conversion of nylon 6 back into caprolactam. When ethyl cyanoacrylate is used as a binder for metal and ceramic powders, it can be recovered for reuse by pyrolysis at 180°C.184 The monomer can be obtained by pyrolysis of polymethyl methacrylate in 92-100% yield,185 poly(a-methylstyrene) in 95-100% yield, and polytetraflu-oroethylene in 97-100% yield.186 Polystyrene can be de-polymerized to styrene containing some styrene dimer by heating with solid acids or bases at 350 400°C.187 It is pos sible that the dimer could be recycled to the next run to produce more monomer. The best yield (> 99% styrene) was obtained by passing polystyrene through a fluidized bed of a solid catalyst at 400 700°C, with a contact time of more than 60 s.188... 

To modify polycarbonates and derivatives of polymethyl methacrylate dichloroethane and dichloromethane media are used. To modify pol5winyl chloride compositions and compositions based on phenolformaldehyde and phenolrubber polymers alcohol or acetone-based media are applied. The FS of metal/carbon nanocomposites are produced using the above media for specific compositions. In IR spectra of all studied suspensions the significant change in the absorption intensity, especially in the regions of wave numbers close to the corresponding nanocomposite oscillations, is observed. At the same time, it is found that the effects of nanocomposite influence on liquid media (FS) decreases with time and the activity of the corresponding suspensions drops. 

Chrysler specified a modified polymethyl methacrylate (PMMA) laminating resin for the body panels of the high-performance sports car, the 400 bhp 10 cylinder Dodge Viper, which went on sale in January 1992. The transition from styling to production took only three years. The decision to use glass fiber reinforced PMMA resin, molded by resin transfer, was a fundamental departure from established Chrysler practice, where previously all main exterior bodywork had been in sheet metal. However, at expected sales of 3000 a year and a unit price of about 50,000, sheet metal would not have been viable and the annual volume was too low to justify injection or compression molded plastics. 

The acrylic polymer which offers the best all-round properties for a metal-coating lacquer exposed to the weather, is the hardest acrylic polymer, polymethyl methacrylate (molecular weight 80 000-150 000). It is hard, clear, scarcely coloured, very little affected by ultra-violet light, insoluble in commercial petrols and resistant to acids and alkalis. Marked deviations from the homopolymer reduce one or... 

Because it is more corrosive than fresh water, salt water not only attacks metals but also degrades even the so-called inert polymers polyethylene, polypropylene, polystyrene, polymethyl methacrylate, etc. (26). Indeed, salt water is very corrosive to adhesive joints. For example, it was reported (27) that exposure to a 5% salt spray for three months had a more severe effect on aluminum joints (stressed DCB) than exposure to a semi-tropical environment for three years. In Table 1, McMillan (27) compares the severity of salt spray with a natural, semi-tropical environment and various in-service conditions. 

Polymethyl methacrylate particles of colloidal dimensions are rather unstable under an electron beam in high vacuum, presumably because of free radical chain depolymerization. Shadowing is thus required. However they even appear to degrade under shadowing by metals such as Pt-Pd alloy, probably as a result of the heat released upon condensation of the metal vapor. Thus electron micrographs of PMMA particles less than 0.30 ym diameter have not been published. This is partly due to background noise due to support films or metal shadowing of various kinds which otherwise would be useful for small PMMA particles. 

The materials originally used in joint replacements were ivory, metals, and glass, but they are fast being replaced by polymeric plastics and ceramics. Polymethyl methacrylate (PMMA), which was the subject of Practice Problem 25.1 B in Section 25.1, and polyethylene have been used in many total joint replacements. However, these joints tend to fail over time when they are implanted in younger, more active patients, so efforts are under way to improve the wear quality of the PMMA and polyethylene parts. 

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