Patent GB-1354982-A (GB)
Title: Neutral membrane and process for making same
IPC: C25B13/08
Filed: 1971-05-26
Abstract: 1354982 Neutral porous polymer membrane ASAHI KASEI KOGYO KK 26 May 1971 [24 July 1970] 17248/71 Headings C3P and C3C [Also in Division B1] A neutral porous membrane comprises a polymer derived from (1) 20-99 wt per cent of one or more monovinyl monomers having non- ionic hydrophilic functional groups; (2) 0-79 wt. percent of one or more non-ionic monovinyl monomers not having hydrophilic functional groups; (3) 1-50 wt. per cent of one or more non-ionic polyvinyl monomers not having hydrophilic functional groups, and (4) 0-90 wt. per cent of a support and (5) 0-50 wt. per cent of one or more reinforcing linear polymers, the percentages being based on the weight of the polymerizable components, the membrane having uniformly distributed therein interconnected micro-pores which are substantially uniform in size. Monomer (1) is preferably vinyl pyrrolidone, hydroxystyrene, 2 - hydroxyethyl (meth)acrylate or a polyoxyethylene mono- (meth)acrylate or combinations thereof; monomer (2) is preferably styrene or methyl methacrylate and monomer (3) is preferably divinyl benzene. The support (4) if present, may be in the form of a woven fabric, fibre cloth or sheet and may be formed from an addition polymer or copolymer, polyvinylalcohol, cellulose, polyamide, polyester wool, silk or mixture thereof. Particularly preferred reinforcing polymers (5) are polystyrene, and styrene/butadiene rubber. The membranes may be prepared by polymerizing so as to form a membrane (e.g. in a cell or in situ on a support, which may be the support (4)), a composition comprising, based on the weight of the polymerizable components; (a) 20-99 wt. per cent of one or more monovinyl monomers having non-ionic hydrophilic functional groups, (b) 0-79 wt. per cent of one or more non-ionic monovinyl monomers not having hydrophilic functional groups, (c) 1-50 wt. per cent of one or more non-ionic polyvinyl monomers not having hydrophilic functional groups, (d) 30-500 wt. per cent of a non-polymerizable diluent or filler which is removable to form interconnected micropores, (e) 0À001-10 wt. per cent of a polymerization initiator, (f) 0-90 wt. per cent of a support and (g) 0-50 wt. per cent of one or more reinforcing linear polymers, and then eliminating 40-100 wt. per cent of the diluent or filler (d) by volatilization or extraction with solvents. A large number of removable components (d) are specified, such as benzene, toluene, ethanol, propanol, butanol, cyclohexanol, glycerine, benzyl alcohol, dioxane, diethyl ether, methethyl ketone, acetone, esters (especially dimethylphthalate), dimethyl formamide, dimethyl sulphoxide, aqueous solutions of NaCl, KCl, MgCl 2  or Na 2 SO 4 , water (all of which are removed by volatilization), and solid substances such as solvent soluble synthetic addition polymers in particulate form. In the example a laminate of a woven polypropylene cloth between two polyester films was impregnated with a monomer composition comprising vinyl pyrrolidone, polyethylene glycol monomethacrylate and divinyl benzene together with azodiisobutyronitrile and dioctylphthalate (as the pore forming component). The assembly was polymerized between glass plates, the polyester films stripped off, and the dioctyl phthalate removed using methanol. The resulting reinforced membrane was a porous semi-permeable membrane.