TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The branched addition copolymer comprises: at least two chains which are covalently linked by a bridge other than at their ends, where the two chains comprise at least one ethylenically monounsaturated monomer, and the bridge comprises at least one ethylenically polyunsaturated monomer; and a residue of a chain transfer agent and optionally a residue of an initiator, where the molar ratio of polyunsaturated monomer(s) to monounsaturated monomer(s) is 1:100-1:4. The branched addition copolymer is prepared from monomers having at least one of hydroxyl, mercapto, amino, carboxylic, epoxy, isocyanate, pyridinyl, vinyl, allyl, (meth)acrylate or styrenyl group. The branched copolymer comprises less than 1% impurity. The branched addition polymer has a weight average molecular weight of 3000-900000 Da. At least one of the monounsaturated monomer(s), polyunsaturated monomer(s) or the chain transfer agent(s) is a hydrophilic or hydrophobic residue. The branched addition copolymer comprises units including styrene, vinylbenzyl chloride, glycidyl methacrylate, 2-vinyl pyridine, 4-vinyl pyridine, methyl acrylate, methyl methacrylate, butyl methacrylate, butyl acrylate, acrylic acid, methacrylic acid, acrylamide, methacrylamide, dimethyl acrylamide, dimethyl(meth)acrylamide, styrene sulfonic acid, 2-acrylamido 2-methylpropane sulfonic acid, divinyl benzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, triethylene glycol dimethacrylate, dodecane thiol, hexane thiol, 2-mercaptoethanol, fragments of azobis isobutyronitrile, di-tert-butyl peroxide or tert-butyl peroxybenzoate (all preferred), ethyl acrylate, ethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxy ethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, allyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, diethylaminoethyl acrylate, vinyl sulfonic acid, vinyl phosphoric acid, tetraethylene glycol dimethacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate or 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione. The film or membrane further comprises: a hardener including dibromopentane, dibromohexane, dibromoheptane, dibromooctane, diiodopentane, diiodohexane, diiodoheptane, diiodooctane, tetramethylhexane-1,6-diaminohexane, tetramethylethylenediamine, tetramethylbutane-1,4-diamine, toluene diisocyanate or hexamethylene diisocyanate; and a support material. Preferred Method: The branched addition copolymer is cured after formation of the branched addition copolymer in the addition polymerization process, where the copolymer is cured: by the addition of a reactive polymer, oligomer or small molecular weight reactive molecule; by means of thermal, photolytic, oxidative, reductive reaction or by the addition of a catalyst or initiator; or by means of the reaction of mutually reactive functional groups provided on the monomers. EXAMPLE - No suitable example given.