Polymer coupling mechanism

Polyheterocycles. Heterocychc monomers such as pyrrole and thiophene form hiUy conjugated polymers (4) with the potential for doped conductivity when polymerization occurs in the 2, 5 positions as shown in equation 6. The heterocycle monomers can be polymerized by an oxidative coupling mechanism, which can be initiated by either chemical or electrochemical means. Similar methods have been used to synthesize poly(p-phenylenes). 

Jones, F.R., Interfacial aspects of glass fibre reinforced plastics. In Jones, F.R. (Ed.), Interfacial Phenomena in Composite Materials. Butterworths, London, 1989, pp. 25-32. Chaudhury, M.K., Gentle, T.M. and Plueddemann, E., Adhesion mechanism of poly(vinyl chloride) to silane primed metal surfaces. J. Adhes. Sci. Technol, 1(1), 29-38 (1987). Gellman, A.J., Naasz, B.M., Schmidt, R.G., Chaudhury, M.K, and Gentle, T.M., Secondary neutral mass spectrometry studies of germanium-silane coupling agent-polymer interphases. J. Adhes. Sci. Technol., 4(7), 597-601 (1990). 

Redistribution in Polymer Coupling. Monomer-polymer redistribution occurs most easily when the monomeric phenol and the phenol of the polymer are identical or, at least, very similar in reactivity (2). The homopolymers of DMP and MPP obviously redistribute very rapidly with either of the two monomers, so that sequential oxidation of DMP and MPP can produce only random copolymer. The redistribution reaction and its relation to the overall polymerization mechanism have been the subject of many previous investigations (2, 10, 13, 14), but the extraordinary facility of redistribution in the DMP-MPP system leads to results that could not be observed in other systems examined. 

Exactly the same result was obtained when the homopolymers were oxidized at — 25°C with a N,N,N, N -tetraethylethylenediamine-cuprous chloride catalyst, conditions which have been reported to cause coupling of DMP homopolymers solely by rearrangement (14). The NMR spectrum of this polymer is shown in Figure 3, together with the spectra of a mixture of homopolymers and of a random copolymer formed by simultaneous oxidation of the monomers. Apparently, dissociation and redistribution occur often enough to determine the structure of the product in this system, even under conditions that favor coupling of polymer molecules by the rearrangement mechanism. 

The reversibility of the reaction is another important feature of coupling by silanes, titanates, and zirconates. The bond formed in the second stage (see chemical reaction above) is not a permanent bond but is an equilibrium reaction which depends on the amount of water in the system. This is the most important concept in the coupling mechanism. Bonds can form, break, and reform. Water immersion affects the interface, causing bond breakage. Bonds can be reformed again if the internal stress in the polymer matrix does not cause permanent delamination which separates the surfaces. 

Gais, H.J., Rupert, S., Modification and immobilization of proteins with polyethylene glycol tresylates and polysaccharide tresylates evidence suggesting a revision of the coupling mechanism and structure of the polymer-polymer linkage. Tetrahedron Lett. 36, 3837-3838, 1995. 

The evolution of olefin polymerization systems over the last 45 years has involved a prolific coupling of polymer science with organometallic chemistry. Successes include the development of catalysts that rival the activities of enzymes and systems that yield polymers possessing structural fidelities approaching 100%. - Central to this success has been a refined understanding of reaction mechanisms and a translation of this understanding into architectural control with specifically designed catalysts. However, despite... 

The mechanism giving rise to the physisorbed polymer is well understood [4] vinylic monomers are reduced, leading to radical anions which dimerize in solution by means of a Radical Radical Coupling mechanism (RRC), and give a di-anion, initiating an... 

The preparation of conducting polymers in emulsion is generally via an oxidative coupling mechanism in which the active polymerizing species are free-radicals. 

Since the assumption of uniformity in continuum mechanics may not hold at the microscale level, micromechanics methods are used to express the continuum quantities associated with an infinitesimal material element in terms of structure and properties of the micro constituents. Thus, a central theme of micromechanics models is the development of a representative volume element (RVE) to statistically represent the local continuum properties. The RVE is constracted to ensure that the length scale is consistent with the smallest constituent that has a first-order effect on the macroscopic behavior. The RVE is then used in a repeating or periodic nature in the full-scale model. The micromechanics method can account for interfaces between constituents, discontinuities, and coupled mechanical and non-mechanical properties. Their purpose is to review the micromechanics methods used for polymer nanocomposites. Thus, we only discuss here some important concepts of micromechanics as well as the Halpin-Tsai model and Mori-Tanaka model. 

The diffusion of solutes through a porous polymer membrane under the temperature gradient is named thermal diffusion or Soret effect. Few studies deal with this phenomenon. Its importance in the transfer through membranes is often neglected compared to the other coupled mechanisms of transfer. 

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