Common cross-linker

The moisture-reactive cross-linkers used in sihcones are of the form R Si(OR )4 where n = 0 or 1 and R may be any organic group, such as methyl, ethyl, or vinyl. R also varies acetoxy, alkoxy, oxime, and propenoxy are among the most typical. Common cross-linkers are hsted in Table 1, and a typical formulation for a one-part sihcone sealant is given in Table 2. 

Figure 5 Selection of common cross-linkers used in molecular imprinting protocols. Both ethyleneglycol dimethacrylate (EDMA) and divinylbenzene (DVB) are very common crosslinkers in molecular imprinting. Other acrylate-based cross-linking monomers conunonly used include the branched cross-linker trimethylolpropane trimethacrylate (TRIM)-[24]. Among the water-soluble cross-linkers, there are phenylene-diacrylamide, V,V-methylene diacrylamide [22], and Z w-acryloylpiperazine [92], which have been used in aqueous systems for the imprinting of, e.g., enzymes.

Table 2 Most common cross-linkers in molecular imprinting, classified according to their nature...

The role of the cross-linker is also important as it will control the morphology of the polymer matrix and also fix the functional group of the monomers around the template. They also stabilize the binding sites and give mechanical stability to the polymers. The type and amount of the cross-linkers have a deep impact on the selectivity and the binding capability of the MIPs. Common cross-linkers are showed in Fig. 2.7. 

Divinyl benzene, with two vinyl groups, is a common cross-linker for chain polymerizations,... 

Small amounts of specially functionalized monomers are often copolymerized with acryUc monomers in order to modify or improve the properties of the polymer. These functional monomers can bring about improvements either directiy or by providing sites for further reaction with metal ions, cross-linkers, or other compounds and resins. Table 9 Hsts some of the more common functional monomers used in the preparation of acryUc copolymers. 

Fillers (qv) are occasionally used in flexible slab foams the two most commonly used are calcium carbonate (whiting) and barium sulfate (barytes). Their use level may range up to 150 parts per 100 parts of polyol. Various other ingredients may also be used to modify a flexible foam formulation. Cross-linkers, chain extenders, ignition modifiers, auxiHary blowing agents, etc, are all used to some extent depending on the final product characteristics desired. 

Moisture-Curing Silicones. The formulation of moisture-curing sHicones includes a sHicone polymer, filler, a moisture-reactive cross-linker, and sometimes a catalyst. The most common sHicone polymer used in sealant formulations is an alternating sHicon—oxygen backbone with methyl groups attached to the sHicon such as the sHicone polymer (1). 

Table 1. Common One-Part Silicone Cross-Linkers and Their Leaving Groups...

Table 5 Commonly Used Monomers, Comonomers, and Cross-Linkers in Contact Lens Polymers... 

In the most succinct sense, a hydrogel is simply a hydrophilic polymeric network cross-linked in some fashion to produce an elastic structure. Thus any technique which can be used to create a cross-linked polymer can be used to produce a hydrogel. Copolymerization/cross-linking free radical polymerizations are commonly used to produce hydrogels by reacting hydrophilic monomers with multifunctional cross-linkers. Water-soluble linear polymers of both natural and synthetic origin are cross-linked to form hydrogels in a number of ways ... 

Free radical copolymerization of a monovinyl compound and a divinyl cross-linker is by far the most commonly employed mode of polymerization for the preparation of organic monoliths. 

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