Epoxide cross-linking

Roumanet, PJ Lafleche, F Jarroux, N Raoul, Y Claude, S Guegan, P. Novel aliphatic polyesters from na oleic acid based monomer. Synthesis, epoxidation, cross-linking and biodegradation. European Polymer Journal, 2013, v. 49 (4), 813-822. 

Since the CTBN and DGEBA are reacted end-on-end-on-end, an ABA block copolymer is formed. Of course, the ordinary epoxide cross-linking reactions are taking place at the same time, so that, in effect, the linear CTBN is joined conterminously with the epoxy network, forming an ABCP-semi-IPN. 

These monomers provide a means for introducing carboxyl groups into copolymers. In copolymers these acids can improve adhesion properties, improve freeze-thaw and mechanical stability of polymer dispersions, provide stability in alkalies (including ammonia), increase resistance to attack by oils, and provide reactive centers for cross-linking by divalent metal ions, diamines, or epoxides. 

AH of the amine hydrogens are replaced when MDA or PMDA reacts with epoxides to form amine based polyols. These polyols can be used in reactions with isocyanates to form urethanes or with additional epoxide to form cross-linked thermo set resins. 

The first type includes vulcanising agents, such as sulphur, selenium and sulphur monochloride, for diene rubbers formaldehyde for phenolics diisocyanates for reaction with hydrogen atoms in polyesters and polyethers and polyamines in fluoroelastomers and epoxide resins. Perhaps the most well-known cross-linking initiators are peroxides, which initiate a double-bond... 

Their main point of difference is that the phenoxies are of much higher molecular weight ( 25 000). The phenoxies are also said to be slightly branched. Like the epoxide resins they are capable of cross-linking via the pendant hydroxyl groups, in this instance by di-isocyanates and other agents. 

As indicated in the preceding section, amine hardeners will cross-link epoxide resins either by a catalytic mechanism or by bridging across epoxy molecules. In general the primary and secondary amines act as reactive hardeners whilst the tertiary amines are catalytic. 

The linear polymer formed is cured hy cross-linking either with an acid anhydride, which reacts with the -OH groups, or hy an amine, which opens the terminal epoxide rings. Cresols and other hisphenols are also used for producing epoxy resins. 

When the epoxide is to be used, a basic curing agent such as a tertiary amine, R3N, is added to cause the individual prepolymer chains to link together. This "cross-linking" of chains is simply a base-catalyzed epoxide... 

FIGURE 3.23 Plots of storage modulus against variable strain for the cross-linked mbber-silica hybrid nanocomposites (a) (ACM)-silica and (b) epoxidized natural mbber (ENR)-silica at different tetraethoxysilane (TEOS) concentrations. (Erom Bandyopadhyay, A., De Sarkar, M., and Bhowmick, A.K., J. Polym. Set, PartB Polym. Phys., 43, 2399, 2005. Courtesy of Wiley InterScience.)... 

FIGURE 3.25 Visual appearance of the pre- and post-aged cross-linked rubber-silica hybrid nanocomposites synthesized from 30 wt% tetraethoxysilane (TEOS) (a) acrylic rubber (ACM)-silica and (b) epoxidized natural rubber (ENR)-silica films of average thickness 0.25 mm. (From Bandyopadhyay, A. and Bhowmick, A.K., Plastic Rubber Comp. Macromol. Eng., 35, 210, 2006. Courtesy of Maney Publishers.)... 

We have cited the case of epoxidation with peracids earlier in this book. A cross-linked polymethacrylic acid can, in principle, be treated with a sulphonic acid catalyst and H2O2 to give the peracid, which will allow epoxidation to be carried out in a convenient way, while the polymer can be reused. The key advantage is that the product stream does not contain an acid, which may be harmful in several ways. 

A chiral diphosphine ligand was bound to silica via carbamate links and was used for enantioselective hydrogenation.178 The activity of the neutral catalyst decreased when the loading was increased. It clearly indicates the formation of catalytically inactive chlorine-bridged dimers. At the same time, the cationic diphosphine-Rh catalysts had no tendency to interact with each other (site isolation).179 New cross-linked chiral transition-metal-complexing polymers were used for the chemo- and enantioselective epoxidation of olefins.180... 

An important factor in all these experiments is the choice of bead used to immobilize the probe. Biochemists have considered cross-linked agarose beads to be exceptionally hydrophilic with a low tendency to bind proteins nonspecifically, and these beads have the further attraction of being commercially available in activated forms (succinimidyl esters, epoxides, and maleimides, for example). However, early trials of bead-based chemical proteomics have shown that many proteins in mammalian cell lysates bind tenaciously to agarose beads. This was unimportant in many studies in which protein-protein interactions were detected by coimmunoprecipitation with immunochemical... 

Kureshy developed a polymer-based chiral Mn-salen complex (Figure 21). Copolymerization of styrene, divinylbenzene, and 4-vinylpyridine generated highly cross-linked (50%) porous beads loaded with pyridine ligands at 3.8 mmol g-1. Once the polymer was charged with the metal complex catalyst, enantioselective epoxidation of styrene derivatives was achieved with ee values in the range 16 46%. 79... 

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