Piperazine-terminated oligomers

In conclusion, some of the high salt rejection properties found with interfacial polypiperazineamide membranes in the laboratory could not be attained by a machine-made membrane. However, the machine-formed membrane may still find applications where high rejection of monovalent salts is not required but where high flux and rejection of larger solutes are useful. A limited effort to replace piperazine in the reaction with piperazine-terminated oligomers did not appear to resolve the membrane reproducability problem. Recent studies made on the use of piperazine terminated oligomers in composite membrane preparation were reported by R. Sudak et al at Membrane Systems, Inc. (46) and by J.F. Wolfe et al at Stanford Research Institute (47). 

Synthesis of piperazine-terminated oligomers as prepolymers for interfacial membrane formation was also examined.46 48 Excess piperazine was reacted with di- and triacyl chlorides in an inert solvent such as 1,2-dichloroethane. The resulting amine-terminated polyamide oligomers had low solubility in the solvent system and precipitated. This served to limit the degree of polymerization of the oligomer. Even so, a portion of the product was insoluble in water and was filtered out during preparation of the aqueous oligomeric amine solution for the interfacial reaction step. 

Piperazine Capping of Epoxy Terminated Siloxane Oligomers... 

An additional way to produce a secondary amine group utilized the reaction of 8 moles of piperazine with 1 mole of the epoxy terminated siloxane oligomer. This reaction was conducted in di-oxane at 60° for about 24 hours. Excess piperazine was removed by washing the oligomer extensively with distilled water. Since the piperazine is water soluble and the oligomer is not, the final system was easily purified to very low levels of residual piperazine in this manner. The product was characterized by titration of the amine endgroups. 

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