The present invention relates to novel co-polymers and their use in the manufacture of porous membranes for haemodialysis application. In particular, such a co-polymer comprises a first segment comprising recurring units poly(aryl ether sulfone) [PAES recurring units], and a second segment comprising-recurring units poly(vinyl pyrrolidone) [PVP recurring units], wherein said first segment and said second segment are linked together via a group of formula O-Ph-NHC(O)C(CH.sub.3).sub.2CH.sub.2.

Composite porous hydrophobic membranes are prepared by forming a perfluorohydrocarbon layer on the surface of a preformed porous polymeric substrate. The substrate can be formed from poly(aryl ether ketone) and a perfluorohydrocarbon layer can be chemically grafted to the surface of the substrate. The membranes can be utilized for a broad range of fluid separations, such as microfiltration, nanofiltration, ultrafiltration as membrane contactors for membrane distillation and for degassing and dewatering of fluids. The membranes can further contain a dense ultra-thin perfluorohydrocarbon layer superimposed on the porous poly(aryl ether ketone) substrate and can be utilized as membrane contactors or as gas separation membranes for natural gas treatment and gas dehydration.

A method for producing a porous polyimide film comprises: forming a first un-burned composite film wherein the first film is formed on a substrate using a first varnish that contains (A1) a polyamide acid or a polyimide and (B1) fine particles at a volume ratio (A1):(B1) of from 19:81 to 45:65; forming a second un-burned composite film wherein the second film is formed on the first film using a second varnish that contains (A2) a polyamide acid or a polyimide and (B2) fine particles at a volume ratio (A2):(B2) of from 20:80 to 50:50 and has a lower fine particle content ratio than the first varnish; burning wherein an un-burned composite film composed of the first film and the second film is burned, thereby obtaining a polyimide-fine particle composite film; and a fine particle removal step wherein the fine particles are removed from the polyimide-fine particle composite film.

A method of manufacturing a porous fluorine-containing polymer membrane is provided, which includes mixing a fluorine-containing polymer, a pore creating agent, and a solvent to form a mixture; forming a membrane of the mixture, and removing the pore creating agent and the solvent in the membrane to form the porous fluorine-containing polymer film. The pore creating agent has a chemical formula of

##STR00001##

wherein R.sup.1 is a C.sub.1-8 alkyl group, a C.sub.2-8 alkenyl group, a C.sub.2-8 alkynyl group, or a C.sub.6-12 aromatic group, and A.sup. is hydrogen sulfite ion, dihydrogen phosphate ion, nitrate ion, halogen ion, or a combination thereof. The solvent has a chemical formula of

##STR00002##

Composite porous hydrophobic membranes are prepared by forming a perfluorohydrocarbon layer on the surface of a preformed porous polymeric substrate. The substrate can be formed from poly (aryl ether ketone) and a perfluorohydrocarbon layer can be chemically grafted to the surface of the substrate. The membranes can be utilized for a broad range of fluid separations, such as microfiltration, nanofiltration, ultrafiltration as membrane contactors for membrane distillation and for degassing and dewatering of fluids. The membranes can further contain a dense ultra-thin perfluorohydrocarbon layer superimposed on the porous poly (aryl ether ketone) substrate and can be utilized as membrane contactors or as gas separation. membranes for natural gas treatment and gas dehydration.

Composite membranes comprising a layer having first and second microporous surfaces and a bulk between the surfaces, the bulk comprising a first set of pores having outer rims, and a second set of pores connecting the rims, and a polymer matrix supporting the first set of pores; and, a second layer having first and second porous surfaces and a second bulk between the porous surfaces, wherein the second bulk comprises a fibrous matrix; or, first and second microporous surfaces and a second bulk between the microporous surfaces, the second bulk comprising: a third set of pores having outer rims and a fourth set of pores connecting the rims, and a polymer matrix supporting the third set of pores; a third set of pores prepared by phase inversion; or, a fibrous matrix; or, a third set of pores prepared by stretching, track etching or e-beam, are disclosed.

A filtration filter used for filtering a liquid chemical for lithography, provided with a polyimide resin porous membrane; a filtration method including allowing a liquid chemical for lithography to pass through the filtration filter; and a production method of a purified liquid chemical product for lithography, including filtering a liquid chemical for lithography by the filtration method.

A method for producing a porous polyimide film comprises: forming a first un-burned composite film wherein the first film is formed on a substrate using a first varnish that contains (A1) a polyamide acid or a polyimide and (B1) fine particles at a volume ratio (A1):(B1) of from 19:81 to 45:65; forming a second un-burned composite film wherein the second film is formed on the first film using a second varnish that contains (A2) a polyamide acid or a polyimide and (B2) fine particles at a volume ratio (A2):(B2) of from 20:80 to 50:50 and has a lower fine particle content ratio than the first varnish; burning wherein an un-burned composite film composed of the first film and the second film is burned, thereby obtaining a polyimide-fine particle composite film; and a fine particle removal step wherein the fine particles are removed from the polyimide-fine particle composite film.

Disclosed is a charged hollow fiber membrane having hexagonal voids for use in high throughput applications. The membrane includes: (i) an inner surface; (ii) an outer surface; (iii) a porous bulk disposed therebetween, wherein the porous bulk comprises at least a first region including: a) a first set of pores having a controlled pore size and having outer rims; b) a second set of pores connecting the outer rims of the first set of pores, wherein the pore size of the first set of pores is greater than the pore size of the second set of pores; and c) a polymer matrix supporting the first set of pores; and (iv) at least one charged zone disposed on the inner surface, on the outer surface, and/or in the porous bulk hollow fiber membrane. Also disclosed is a method for preparing such hollow fiber membranes, which involves coating a filament with a coating composition that includes a membrane-forming polymer, a charged polymer, and dissolvable nanoparticles, followed by phase invention, dissolving of the nanoparticles, and removal of the filament.

A double-skinned membrane that includes a polymeric support having a thickness of 20 to 500 nm, a first surface and a second surface opposed to each other; a polymeric thin film layer having a thickness of 1 to 1000 nm and covering the first surface; and a sulfonated pentablock copolymer layer having a thickness of 1 to 1000 nm and covering the second surface. Also disclosed is a method of preparing the above-described double-skinned membrane.