Polymerization process of sulphonic monomers

A polymerization process in aqueous emulsion of:

• (I) one or more fluorinated monomers containing at least one ethylene unsaturation;
• (II) one or more fluorinated monomers containing sulphonyl groups —SO2F;
• said process comprising:
• reactor purging, monomer (II) introduction in liquid form into the reactor, reactor pressurization with gaseous monomers (I);
• addition of at least one surfactant of formula:
• Rf—X−M+
• wherein:
• X is equal to —COO, —SO3;
• M is selected from H, NH4, alkaline metal;
• Rf represents a (per)fluoropolyether chain, preferably having number average molecular weight comprised between about 230 and about 1,800, preferably from 300 to 750, said (per)fluoropolyether chain comprising repeating units selected from one or more of the following:
• a) —(C3F6O)—;
• b) —(CF2CF2O)—;
• c) —(CFL0O)—, wherein L0=—F, —CF3;
• d) —CF2(CF2)z′CF2O—, wherein z′ is an integer 1 or 2;
• e) —CH2CF2CF2O—;
• Rf is monofunctional, and has a (per)fluorooxyalkyl end group T, optionally in the (per)fluoroalkyl end groups one fluorine atom is substituted by one chlorine or hydrogen atom;
• addition of the initiator, and during the polymerization feeding of monomers (I) so as to maintain constant the reactor pressure;
• optionally further addition of monomer (II) and chain transfer agents.