Epichlorohydrin, cross-linker

Organic cross-linkers, which include glyoxal (48) and formaldehyde (qv), have also been used. Use of hypohaUte salts (49) and epichlorohydrin (50) promotes gel stabiUty. Phenol—formaldehyde cross-linking systems have been used to produce stable acrylamide copolymer gels at temperatures above 75°C and brine hardness levels above 2000 ppm (51). 

Zhu and coworkers have reported the synthesis of functionalized poly(vinyl alcohol) resins for use as scavengers [13]. This was achieved via inverse suspension polymerization along side epichlorohydrin as a cross-linker. These resins were found to have excellent swelling characteristics in DMF, CH3OH, dioxane, THF, CH2C12 and H20. These were then functionalized with glutaric aldehyde to provide a polymer-supported aldehyde (Scheme 8.8). 

Modification of the CDs either with glucosyl, maltosyl, hydroxypropyl, hydrox-yethyl, methyl or sulfate groups increases their aqueous solubihty. Modification of CDs with low aqueous solubility or those that are insoluble in water can be achieved by adding aliphatic groups or short nonpolar groups to the cyclodextrin or by cross-linking CDs with a suitable cross-linker, such as epichlorohydrin, to form spherical beads of polymers. These modified CDs have the same functional properties as the immodified CDs such as stabilization of guests, etc. [3]. 

The most conunonly used cross-linkers for CS membranes are epichlorohydrin (ECH) and glutaraldehyde (GA, Rgure 16.11). In literature, one can also find the other cross-linkers like toluene isocyanate and sodium tripolyphosphate (TPP). Most recently, Mio et al. [55] prepared amphoteric thin film NF membrane using sulfated CS as the active layer on to the surface of PSf UF support followed by cross-linking using ECH. The membranes were tested for salt rejection application. The membranes showed a maximum of 90.8% Na2S04 (with 22.9 kg h permeate flux) and 32.5% NaCl (with 58.4 kg-2 h- permeate flux) rejection, respectively, at 0.4 MPa pressure for 1000 mg/L feed concentrations. Thus, they concluded that the resultant cross-linked SCS/PSf membranes... 

Ether cross-linker Polyether CD-based polymers are mostly prepared from epoxides opening in basic conditions [7]. The most widely used epoxides are epichlorohydrin (EPI) and its nontoxic equivalent, the ethylene glycol diglycidyl ether (EGDE) (Scheme 2.3). 

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