Reverse Osmosis Membrane with Branched Poly(Alkylene Oxide) Modified Antifouling Surface

Abstract

Composite membranes that exhibit long-term resistance to biofouling comprise a porous support and a crosslinked polyamide discriminating layer having an external surface, the discriminating layer comprising a branched poly(alkylene oxide) (PAO) polymer attached to its external surface. The branched PAO polymer typically has the structure of a molecular comb or brush, and is made by polymerization of a PAO macromonomer of the following formula: RO—[(CHR′) n —O] m -V in which R is hydrogen or a C 1-20 aliphatic or aromatic group, V is any group containing a polymerizable site, each R′ is independently hydrogen or a short chain alkyl group, n is an integer of 1-6, and m is an integer of 1 to about 200. The α end group can be either polymerized or copolymerized.

1 . A composite membrane comprising a porous support and a crosslinked polyamide discriminating layer having an external surface to which are attached crosslinkced, branched poly(alkylene oxide) (PAO) polymers, the polymers having a relative weight average molecular weight before crosslinking, as measured by size exclusion chromatography against a linear PEO standard, of at least about 5,000.  
   
   
       2 . The composite membrane of  claim 1  in which the branched PAO polymers comprise derivatives of PAO macromonomers of the formula:  
       RO—[(CHR′) n —O] m V  (I)  
     in which R is hydrogen or a C 1-20  aliphatic or aromatic group, V is any group containing a polymerizable site, each R′ is independently hydrogen or a short chain alkyl group, n is an integer of 1-6, and m is an integer of 1 to about 200.  
   
   
       3 . The composite membrane of  claim 2  in which R is a C 1-20  alkyl group, V is a derivative of at least one of p- and m-vinyl benzene, p- and m-vinyl benzoic acid, methacryloyl chloride, acryloyl chloride and isopropenyl oxazoline, R′ is hydrogen or methyl, n is 2 or 3, and m is an integer between about 3 and about 50.  
   
   
       4 . The composite membrane of  claim 3  in which R is a C 1-12  alkyl group, V is a derivative of methacryloyl chloride, R′ is hydrogen, n is 2, and m is an integer between about 7 and about 25.  
   
   
       5 . The composite membrane of  claim 4  in which the relative weight average molecular weight of the PEO brush is at least about 10,000.  
   
   
       6 . A branched poly(alkylene oxide) polymer having a relative weight average molecular weight, as measured by size exclusion chromatography against a linear PEO standard, of at least about 5,000, the polymer prepared by the copolymerization of poly(alkylene oxide) and glycidyl methacrylate under atom transfer radical polymerization (ATRP) conditions.  
   
   
       7 . The branched polymer of  claim 6  in which the ATRP conditions include an organic solvent as the polymerization medium.  
   
   
       8 . The branched polymer of  claim 6  in which the ATRP conditions include water as the polymerization medium.  
   
   
       9 . The branched polymer of  claim 6  in which the ATRP conditions include CuBr/2,2′-bipyridine/ethyl 2-bromoisobutyrate as a polymerization initiator.  
   
   
       10 . A branched poly(alkylene oxide) polymer having a relative weight average molecular weight, as measured by size exclusion chromatography against a linear PEO standard, of at least about 5,000, the polymer prepared by the copolymerization of poly(alkylene oxide) and glycidyl methacrylate with a free radical initiator.  
   
   
       11 . The branched polymer of  claim 10  in which the free radical initiator is azobisisobutyronitrile.  
   
   
       12 . A branched poly(alkylene oxide) polymer having a relative weight average molecular weight, as measured by size exclusion chromatography against a linear PEO standard, of at least about 5,000, the polymer prepared by the copolymerization of poly(alkylene oxide) and 2-isopropenyl-2-oxazoline under ATRP or free radical initiator conditions.  
   
   
       13 . A method of desalting brine, the method comprising passing the brine through a composite membrane comprising a porous support and a crosslinked polyamide discriminating layer having an external surface to which are attached branched, crosslinked poly(alkylene oxide) polymers, the polymers having a relative weight average molecular weight before crosslinking, as measured by size exclusion chromatography against a linear PEO standard, of at least about 5,000.  
   
   
       14 . A method of treating unpurified water to produce purified water, the method comprising passing the unpurified water through a composite membrane comprising a porous support and a crosslinked polyamide discriminating layer having an external surface to which are attached branched, crosslinked poly(alkylene oxide) polymers, the polymers having a relative weight average molecular weight before crosslinking, as measured by size exclusion chromatography against a linear PEO standard, of at least about 5,000.  
   
   
       15 . A method of preparing a branched poly(alkylene oxide) polymer having a relative weight average molecular weight, as measured by size exclusion chromatography against a linear PEO standard, of at least about 5,000, the method comprising copolymerizing poly(alkylene oxide) and glycidyl methacrylate under atom transfer radical polymerization (ATRP) conditions.  
   
   
       16 . A method of preparing a composite membrane comprising a porous support and a crosslinked polyamide discriminating layer having an external surface to which are attached branched, crosslinked poly(alkylene oxide) polymers, the method comprising coating the external surface of the discriminating layer with a branched, crosslinked PAO polymer having a relative weight average molecular weight before crosslinking, as measured by size exclusion chromatography against a linear PEO standard, of at least about 5,000.  
   
   
       17 . A method of preparing a composite membrane comprising a porous support and a crosslinked polyamide discriminating layer having an external surface to which are attached branched, crosslinked poly(alkylene oxide) polymers, the method comprising coating the external surface of the discriminating layer with a branched PAO polymer having a relative weight average molecular weight before crosslinking, as measured by size exclusion chromatography against a linear PEO standard, of at least about 5,000, and then subjecting the branched PAO polymer attached to the external surface of the discriminating layer to crosslinking.  
   
   
       18 . A composite membrane that exhibits a performance level at least as effective removal of debris accumulated during use in a biofouling environment as before its use in such an environment, the membrane comprising a porous support and a crosslinked polyamide discriminating layer having an external surface to which are attached crosslinked, branched poly(alkylene oxide) polymers, the polymers having a relative weight average molecular weight before crosslinking, as measured by size exclusion chromatography against a linear PEO standard, of at least about 5,000.  
   
   
       19 . The membrane of  claim 18  in which the crosslinked, branched PAO polymer is a copolymer of PEO and glycidal methacrylate.