Forming a treated switchable polymer and use thereof in a forward osmosis system

A process of forming a treated switchable polymer, comprising:

• providing a switchable polymer that is switchable between a first form and a second form, the switchable polymer comprising switchable moieties, each switchable moiety being switchable between a neutral form associated with the first form of the switchable polymer, and an ionized form associated with the second form of the switchable polymer, the switchable polymer:
• having ≥3 mmol switchable moieties per gram of switchable polymer,
• having a pKaH of about 7 to about 14, and
• being resistant to hydrolysis;
• and
• treating the switchable polymer to remove non-polymeric and oligomeric contaminants to form the treated switchable polymer;
• the treated switchable polymer is switchable between a third form and a fourth form, the neutral form of each switchable moiety being associated with the third form of the treated switchable polymer, and the ionized form of each switchable moiety being associated with the fourth form of the treated switchable polymer, the third form of the treated switchable polymer having a first osmotic pressure in aqueous solution, and the fourth form of the treated switchable polymer having a second osmotic pressure in aqueous solution, the ratio of the second osmotic pressure to first osmotic pressure being at least 6:1;
• the treated switchable polymer being substantially water soluble in the fourth form;
• wherein the switchable polymer is poly(N-methyl-N,N-diallylamine) (PDMAAm), poly(N-methylpropenimine) (PMPI), poly(diallylmethylamine) (PDAMAm), poly(N-[3-(dimethylamino)propyl]-methacrylamide), poly(N,N-dimethylallylamine) (PDMAPMAm), poly(1,4-bis(dimethylamino)-2-butene), poly(N,N-di(N′,N′-dimethylbutylamine)allylamine), poly(N,N,N′,N′-tetramethyl-1,2-ethylenediamine), poly(N-methylbutyleneimine), poly(N-tertbutylallylamine), or a copolymer thereof.