Carboxy/epoxy

Other immobilization methods are based on chemical and physical binding to soHd supports, eg, polysaccharides, polymers, glass, and other chemically and physically stable materials, which are usually modified with functional groups such as amine, carboxy, epoxy, phenyl, or alkane to enable covalent coupling to amino acid side chains on the enzyme surface. These supports may be macroporous, with pore diameters in the range 30—300 nm, to facihtate accommodation of enzyme within a support particle. Ionic and nonionic adsorption to macroporous supports is a gentle, simple, and often efficient method. Use of powdered enzyme, or enzyme precipitated on inert supports, may be adequate for use in nonaqueous media. Entrapment in polysaccharide/polymer gels is used for both cells and isolated enzymes. 

The carboxy/epoxy system displays a very fast lacquer type dry but, in comparison to a 2 pack polyurethane, relatively slow through cure. Tertiary amines can be used to enhance the cure of the coating. However, careful selection of the catalyst is critical since some amines can also make the coating water sensitive. There is also the potential to catalyse the system internally by incorporating an amine functional monomer onto the backbone of the acrylic resin by copolymeiisation of amine functional acrylic or vinyl monomers. 

The market development of these products has had to depend on specific performance improvements offered by each of the technologies. For example, the very fast dry and high durability of the carboxy/epoxy and amine/epoxy technologies have been successfully developed in the transport, ACE, machinery enamel and heavy duty areas. 

Epoxy/Carboxy Cure Sites. Epoxy/carboxy cure sites probably represent the most important alternative to labile chlorine containing monomers. There has been increasing interest in them due to the discovery of the highly efficient quaternary ammonium salt-based accelerators (29—34). The reaction between the epoxy ring and carboxyUc acid can happen in the following three ways ... 

This low viscosity resin permits cure at low (70°C) temperatures and rapidly develops excellent elevated temperature properties. Used to increase heat resistance and cure speed of bisphenol A epoxy resins, it has utihty in such diverse appHcations as adhesives, tooling compounds, and laminating systems. A moleculady distilled version is used as a binder for soHd propellants (see Explosives and propellants) and for military flares (see Pyrotechnics). Its chief uses depend on properties of low viscosity and low temperature reactivity, particularly with carboxy-terminated mbbers. 

Dihydroxy-16a-carboxy- 157 3/3,21 -Dihydroxy-16a, 17a-epoxy- 779 3,20-Dioxo-16 -carboxy- 157 3/3-Hydroxy-16a-acetoxy-20-oxo- 514 17a-Hydroxy-3/ ,21-diacetoxy-20-oxo- 778 3/3-Hydroxy-16a, 17a -epoxy-20-oxo- 779... 

Poly(unsaturated ester)-siloxane segmented copolymers have been prepared by the polycondensation of epoxy-terminated polydimethylsiloxanes and carboxy-terminated poly(ethylene adipate-co-maleate) oligomers 243). Reactions have been conducted in cellosolve solvent, at 140-150 °C, in the presence of 2% by weight potassium hydroxide catalyst. The molecular weights reported were fairly low. The same group has also prepared poly(hexamethylene adipate)-polydimethylsiloxane copolymers con-... 

Polybutadiene-polydimethylsiloxane segmented copolymers were prepared by the reaction of epoxy-terminated PDMS and carboxy-terminated polybutadienes, in refluxing toluene under catalytic action of potassium hydroxide 243). Molecular weights of the copolymers obtained were usually in the low range. No other characterization data were available. 

Furthermore, marked substrate selectivity was noted, such that the rate of reaction decreased the series in the order 14,15-epoxy > 11,12-epoxy > 8,9-epoxy > 5,6-epoxy. In other words, the more removed the oxirane ring was from the carboxy group, the faster its enzymatic hydration. It was suggested that the low reactivity of 5,6-EET is related to its possible physiological functions. 

Hydroxy-terminated polybutadiene (HTPB) is considered to be the best binder for obtaining high combustion performance, superior elongation properties at low temperatures, and superior mechanical strength properties at high temperatures. This combination of properties is difficult to achieve in double-base propellants. HTPB is characterized by terminal -OH groups on a butadiene polymer. The other type of butadiene polymer used is carboxy-terminated polybutadiene (CTPB), which is cured with an imine or an epoxy resin. It should be noted that CTPB is somewhat sensitive to humidity, which has an adverse effect on its ageing charac-... 

Compatibility. Owing to the high reactivity of the isocyanate group, polyurethane propellants require a more sophisticated processing technique than the rather foolproof, carboxy-terminated polybutadiene aziri-dine and/or epoxy-cured propellant systems. Processing is even more complicated if bonding agents (see below) are present, which are used to bolster mechanical properties in practically any modern propellant. 

An evaluation was conducted to identify the benefits that might accrue when ZAs were used in high solid polyesters, high solid epoxies, and conventional alkyds, in each instance the coating being applied to two or more different surfaces. Recognizing that alkyds and polyesters are both characterized by available carboxy and hydroxy groups, the decision was made to evaluate amino and carboxy ZAs in these systems (Table 3). 

Thus, in alkyd, polyester, and epoxy coatings applied to CRS, phosphatized steel, and aluminum, the use of ZAs APG (aminofunctional) and CPG (carboxy-functional) has allowed for the virtual elimination of blister formation and corrosion after 300 h of salt fog exposure. The use of multifunctional ZAs in a Kraton base adhesive has allowed for a 52% increase in T-peel strength on EPDM rubber when compared with the same adhesive containing aminofunctional silane. Incorporation of mercaptofunctional ZA into crosslinkable elastomers has... 

In the first step (Eq. (8)), a binary complex of the proton donor and epoxy oxygen is formed. On addition of the anhydride, a ternary transition complex is formed which decomposes to a diester bearing a secondary hydroxy group (Eq. (9)). If the proton donor is a carboxy group, a monoester is formed and the carboxy group is... 

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