Screening of high-efficiency crosslinking agents for poly(N,N-dimethylaminoethyl methacrylate) and performance of its nanofiltration membranes

Poly(N,N-dimethylaminoethyl methacrylate) (PDM) is a water-soluble polymer that can be crosslinked via a quaternization reaction that takes 4–20 h. Polyhalogenated hydrocarbons with different structures were screened to identify high-efficiency crosslinking agents for PDM. For this purpose, the gelation time of bulk crosslinked PDM and the separation performance of interfacially crosslinked PDM membranes were investigated. Use of bromohydrocarbons with benzylic and allylic types and high functional group density can afford the rapid quaternization reaction of PDM. PDM nanofiltration membranes were prepared via interfacially crosslinking PDM with 1,3,5-tris(bromomethyl)benzene (TBB), and the effects of membrane preparation conditions (including PDM concentration, coating time, TBB concentration, and crosslinking time) on the permeation and separation performances of as-prepared membranes were investigated. The PDM membrane prepared at a PDM concentration of 6 g/L, TBB concentration of 40 mmol/L, coating time of 30 s, and crosslinking time of 30 s exhibited a water flux of 20.3 L/(m2·h) and a salt rejection of 90%, when the membrane was treated with a 1000 mg/L MgSO4 aqueous solution at 0.8 MPa pressure. The PDM membrane was positively charged and the extent of salt rejection followed the order MgCl2 > NaCl ≈ MgSO4 > Na2SO4. The membrane also exhibited good antifouling properties and chlorine resistance.