Process crosslinking

It is a characteristic feature of this copolymerization, as in general of binary systems in which one of the monomers is a diene, that with the progress of the reaction a secondary crosslinking process becomes possible. 

Polyester-based networks are typically prepared from polyester prepolymers bearing unsaturations which can be crosslinked. The crosslinking process is either an autoxidation in the presence of air oxygen (alkyd resins) or a copolymerization with unsaturated comonomers in the presence of radical initiators (unsaturated polyester resins). It should also be mentioned that hydroxy-terminated saturated polyesters are one of the basis prepolymers used in polyurethane network preparation (see Chapter 5). 

Another commercially important crosslinking process that involves unsaturated polymer precursors is the so-called drying of alkyd resins in paints. This process is not drying at all, at least not in the sense of mere loss of solvent to leave behind a solid residue. Instead, the main process is the conversion of high relative molar mass molecules to a crosslinked structure via... 

The products of the chemical degradation of PETP with triethylene tetramine and triethaneolamine can be used as epoxy resin hardeners, it is demonstrated. Products of PETP aminolysis with triethylene tetramine and aminoglycolysis with triethanolamine, were characterised using NMR and rheometric measurements. Characteristics of the crosslinking process for the system epoxy resin/ PETP/amine degradation product, and epoxy resin/TETA for comparison were investigated by DSC. Three classes of liquid epoxy resins based on bisphenol A, bisphenol F and epoxy novolak resins were used in the experiments. 16 refs. 

Copolymerization and crosslinking processes are very important in the paint and coating industry. The theoretical description of such processes is helpful in understanding the essential parameters in these complex operations and in improving process conditions and product specifications with a minimum of time-consuming systematic experiments. 

Finally, a new water-soluble polyphosphazene was recently synthesized that has the structure shown in 36 (46). This polymer has two attributes as a biomedical macromolecule. First, the pendent carboxylic acid groups are potential sites for condensation reactions with amines, alcohols, phenols, or other carboxylic acid units to generate amide, ester, or anhydride links to polypeptides or bioactive small molecules. Second, polymer forms ionic crosslinks when brought into contact with di- or trivalent cations such as Ca or Ai3+. The crosslinking process converts the water-soluble polymer to a hydrogel, a process that can be reversed when the system... 

The structural changes that occur at 90<>C are again indicative of steric constraints. We find no evidence that the N-H bonds in the -[PhSiHNH]x backbone participate in the crosslinking process observed in (30) which is in keeping with our observation concerning piperidine s lack of reactivity. We also observe similar behavior for reactions of n-hexylsilane with N1I3 (23). 

The crosslinking process should not be considered to be completely homogeneous. Several phenomena might cause inhomogeneities. On a molecular scale, we... 

Summary Catalytic crosslinking processes of organosilicon preceramic polymers using transition metal complexes as well as stoichiometric reactions between such polymers and transition metal complexes and powders that lead to new ceramic phases are reviewed. 

For all calculations, the factor / has been set to unity, since the crosslinking process occured in bulk.)... 

This process involves the suspension of the biocatalyst in a monomer solution which is polymerized, and the enzymes are entrapped within the polymer lattice during the crosslinking process. This method differs from the covalent binding that the enzyme itself does not bind to the gel matrix. Due to the size of the biomolecule it will not diffuse out of the polymer network but small substrate or product molecules can transfer across or within it to ensure the continuous transformation. For sensing purposes, the polymer matrix can be formed directly on the surface of the fiber, or polymerized onto a transparent support (for instance, glass) that is then coupled to the fiber. The most popular matrices include polyacrylamide (Figure 5), silicone rubber, poly(vinyl alcohol), starch and polyurethane. 

Glutaraldehyde was one of the first and still is one of the most commonly used crosslinking agents available for creating antibody-enzyme conjugates. The crosslinking process using... 

Avoid covalently linking the A and B chains together during the crosslinking process. This can be done by using heterobifunctional crosslinkers that are more controllable in their reactivity than homobifunctional reagents. 

The crosslinking process must minimize polymerization of either the antibody or the toxin. Low molecular weight, 1 1 or 1 2 conjugates of antibody-to-toxin are best. 

React for 2 hours at room temperature. If liposome aggregation or protein precipitation occurs during the crosslinking process, scale back the amount of EDC added to the reaction. 

Mass spec analysis of the peptide fragments formed by this process yields pairs of MS peaks differing only by the mass change caused by the substitution of deuterium atoms for hydrogen atoms in half of the crosslinks. Thus, searching for MS peaks in the data that differ by the number of deuterium substitutions immediately will identify peptides from the interacting proteins that have been captured by the crosslinking process. 

Figure 28.7 Reaction of a PIR compound with a protein sample can result in several products, all of which can be identified by mass spec analysis. A true inter-protein crosslink can occur that links two interacting proteins together, which is the desired product. However, the crosslinking process also may result in intra-protein crosslinks or dead ends wherein only one end of the PIR reagent has coupled to a protein.

Therefore, in a crosslinking process which is governed by the intramolecular crosslinking, the structure of the microgels is important. Currently, gel formation is qualitatively quite well understood by using the knowledge about the properties of microgels. However, a satisfactory quantitative treatment is still desirable. 

Figure 4. Crosslinking process via electrophilic aromatic substitution.

By interactive in this context we mean that the filler can adsorb network polymer and thereby become involved in the crosslinking process, creating a larger number of network links. In some cases the polymer-particle interaction may be the main crosslinking mechanism. 

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