Surface active initiators Applications

Tauer, K. and Kosmella, S. (1993) Synthesis, characterisation and application of surface active initiators. Polym. Int., 30, 253. 

To realize surface-bonded initiating sites or their precursors, a variety of methods are applicable. Either organic (polymer) surfaces are irradiated or plasma treated to yield suitable functional groups [187, 195] or inorganic supports are covered with an interlayer of functional polymers bearing the desired groups. However, to gain control over the quantity of surface reaction sites and define the surface chemistry, interlayers of low molar mass a,co-functionalized surface active compounds are suit-... 

Cyanoacrylate adhesives (Super-Glues) are materials which rapidly polymerize at room temperature. The standard monomer for a cyanoacrylate adhesive is ethyl 2-cyanoacrylate /7085-85-0], which readily undergoes anionic polymerization. Very rapid cure of these materials has made them widely used in the electronics industry for speaker magnet mounting, as well as for wire tacking and other applications requiring rapid assembly. Anionic polymerization of a cyanoacrylate adhesive is normally initiated by water. Therefore, atmospheric humidity or the surface moisture content must be at a certain level for polymerization to take place. These adhesives are not cross-linked as are the surface-activated acrylics. Rather, the cyanoacrylate material is a thermoplastic, and thus, the adhesives typically have poor temperature resistance. 

Lecithin has some catalytic or cocatalytic effects in multiphase systems because of its surface-active properties. Lecithin is reported to be useful as an emulsifier in the curing of aqueous dispersions of unsaturated polyesters (337). The products are more easily removed from their molds and have improved mechanical properties when lecithin is used. In a fermentation application, 1.5% soybean lecithin acts as an inducer in the preparation of cholesterol esterase using a strain of Pseudomonas bacteria (338). Aside from its role as a catalyst, initiator, or modifier, lecithin may have ancillary uses in catalyst systems as part of a protective coating (339). 

The fact that the gaseoues reactants react very quickly means that, in practice and according to model B, the reaction takes place at the phase boundary or in an interfacial layer with a relatively small thickness [30, 32], The latter has been proven which - via process modeling on the basis of appropriate kinetic models -made possible a more optimal reactor and mixing design [43], Additionally, there is much (industrially initiated) work underway to check the addition of counterions or surface active ligands (Sections 3.2.4 and 3.2.6) or to test measures which increase the widths of the interfacial layers or the consequences of micelle/vesicle-forming devices (Section 4.5) [45]. The dependence of the reactivity of aqueous systems on the solubility of the reactants in the aqueous catalyst solutions is of appreciable importance for the problem of universal applicability (cf., e.g., Sections 4.1, 4.2, 6.1.3.2, and Chapter 7). 

The most common methnd of manufacturing activated carbons for vapor-phase applications is by gas activation. This method is employed for granular forms of activated carbon, The material is formed and initially calcined at 400-500 C, This material is then selectively oxidized ai 8DO-IOOO°C to develop porosity and surface activity. The higher temperature in combination with steam, carbon dioxide, Or flue gas is preferred since ihe reaction is less exothermic and easier to control than low-temperature oxidation with air. 

Other examples of peroxy inisurfs can also be found in Russian scientific papers. As for instance in Ref. [41] Voronov et al. describe a polymeric surfactant with peroxy side chains for application as inisurfs in emulsion polymerization. They obtained the polymeric inisurf (Inisurf 2) by copolymerization of a peroxide containing monomer (dimethyl-vinylethinyl-methyl-tm-butyl-peroxide) with acrylic or methacrylic acid or 2-methyl-5-vinyl pyridine with benzoyl peroxide as initiator in the presence of dodecylmercaptan as chain transfer agent. The resulting copolymers are water soluble at appropriate pH-values, surface active, and exhibit a critical micelle concentratioiL... 

Some examples of monomeric surface-active azo initiators as well as their synthesis, application in emulsion polymerization, and resulting latex properties are described in Refs. [43, 44]. These inisurfs are symmetrical and exhibit a methylene chain as hydrophobic part of the molecule and an ionic hydrophilic group (Inisurf 4, Inisurf 5). The main residts of these investi tions may be summarized as follows ... 

Association of Textile Chemists and Colorists recently [3] described the incorporation of small amoimts of fluorocarbon derivative in a polymeric material normally used to treat textiles for water repellency. They observed that the fluorocarbon preferentially adsorbed at the interfaces and decreased the values to 16 to 18 dynes per cm. Their films clearly showed the ability to self-heal, for when the initially adsorbed layer was deliberately scraped off, additional molecules quickly adsorbed at the interface when the polymer matrix was recured at an elevated temperature. The usefulness of adsorbed films of surface active molecules is thus apparent, and one may expect wide application of this technique to specific problems. The present study, in combination with previous investigations of wettability and surface activity in organic liquids, forms an excellent guide for the design and synthesis of further surface active agents for polymeric systems. 

Both alloy electrodes were reported to be quasi-reversible with respect to the dissolution of the surface atoms of the less noble components, that is, they establish partial equilibrium between the solution and the surface atoms (rather than with the bulk atoms) of the less noble components, Cu and Ag, respectively. Thus, by application of the Nemst equation, the normalized surface activities of these components that result from galvanostatic anodic pulses could be determined from the chronopotentiograms and were shown to be lower than the initial activities prior to anodic current flow. In addition to this, it could be shown that upon an interruption of the appKed current the initial potential, and hence the initial activity of the less noble alloy component, is reestablished, in the course of time, due to relaxation processes that induce a reorganization of the atoms in the electrode surface [4,112]. 

Since bases are catalysts for the curing reaction and acids are stabilizers for the cyanoacrylates, the pH value of the surface will control the cure speed. Surfaces that tend to be acidic will cure slowly compared to a neutral surface, which in turn will cure more slowly than an alkaline surface. In most applications the objective is to speed the cure therefore, all the commercially available activators are weak bases dissolved in a volatile carrier. Applying an activator to a surface places a layer of the weak base in position to initiate the cure. Since they are stronger bases than moisture, they are able to neutralize the stabilizer systems in the adhesive more effectively, and thus they can tolerate larger gaps than would be possible with moisture alone. In general, the fixturing time is 10 times faster with activator than without it. Even with activator, the effect of the gap is clear (see Table 4). 

A wide variety of natural and synthetic materials have been used for biomedical applications. These include polymers, ceramics, metals, carbons, natural tissues, and composite materials (1). Of these materials, polymers remain the most widely used biomaterials. Polymeric materials have several advantages which make them very attractive as biomaterials (2). They include their versatility, physical properties, ability to be fabricated into various shapes and structures, and ease in surface modification. The long-term use of polymeric biomaterials in blood is limited by surface-induced thrombosis and biomaterial-associated infections (3,4). Thrombus formation on biomaterial surface is initiated by plasma protein adsorption followed by adhesion and activation of platelets (5,6). Biomaterial-associated infections occur as a result of the adhesion of bacteria onto the surface (7). The biomaterial surface provides a site for bacterial attachment and proliferation. Adherent bacteria are covered by a biofilm which supports bacterial growth while protecting them from antibodies, phagocytes, and antibiotics (8). Infections of vascular grafts, for instance, are usually associated with Pseudomonas aeruginosa Escherichia coli. Staphylococcus aureus, and Staphyloccocus epidermidis (9). 

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