Abstract: The present invention concerns a process for preparing a polymer comprising at least one gel polymerization step (E) in which the following are contacted: ethylenically unsaturated water-soluble monomers, the same or different; a source of free radicals adapted to the polymerization of the said monomers, typically a redox system; and a radical polymerization control agent, preferably comprising a thiocarbonylthio —S(C?S)— group; with a concentration of monomers in the reaction medium of step (E) sufficiently high to cause gelling of the medium if polymerization was conducted without the control agent.

Abstract: The present invention relates to a method for preparing a polymer based on N-vinyl lactam monomer units, which comprises a step (E) for controlled radical polymerization of a composition comprising: monomers containing (and most often consisting of) N-vinyl lactam monomers, either identical or different (and generally identical); an agent for controlling the radical polymerization, for example comprising a thiocarbonylthio group —S(C?S)—; and a radical polymerization initiator which is a redox system comprising a reducing agent (Red) and an oxidizing agent (Ox).

Abstract: The present invention relates to a method for preparing a polymer based on N-vinyl lactam monomer units, which comprises a step (E) for controlled radical polymerization of a composition comprising: monomers containing (and most often consisting of) N-vinyl lactam monomers, either identical or different (and generally identical); an agent for controlling the radical polymerization, for example comprising a thiocarbonylthio group —S(C?S)—; and a radical polymerization initiator which is a redox system comprising a reducing agent (Red) and an oxidizing agent (Ox).

Abstract: The present invention concerns a process for preparing a polymer comprising at least one gel polymerization step (E) in which the following are contacted: ethylenically unsaturated water-soluble monomers, the same or different; a source of free radicals adapted to the polymerization of the said monomers, typically a redox system; and a radical polymerization control agent, preferably comprising a thiocarbonylthio —S(C?S)— group; with a concentration of monomers in the reaction medium of step (E) sufficiently high to cause gelling of the medium if polymerization was conducted without the control agent.

Abstract: The present invention relates to a bismuth-type promoter and its use as a Lewis acid catalyst for acylation reactions of aromatic compounds. The promoter corresponds to the formula MY&mgr;−q&xgr;q, where M represents a &mgr;-valent and at least trivalent element in the cationic form, preferably known to give Lewis acids, where Y is a monovalent anion or a monovalent anionic functional group, where &xgr;− represents an anion or an anionic functional group carrying a sulfonyl functional group carried by a perhalogenated atom, preferably a perfluorinated atom, more preferably a perfluoromethylene (—CF2—); and where q is an integer advantageously chosen within the closed range (comprising the limits) ranging from 1 to (&mgr;−1) (that is to say, 1 or 2 when &mgr; is 3). The present application also relates to processes for the preparation of the promoter.