Process for the isolation of sulfonyl fluoride polymers and polymers obtained therefrom
The invention relates to a process for the isolation of (per)fluorinated polymers containing sulfonyl fluoride functional groups from a polymerization latex. The process comprises adding the polymerization latex to an aqueous electrolyte solution under high shear stirring at a temperature equal to or lower than the glass transition temperature of the polymer. The invention further relates to the (per)fluorinated polymers containing sulfonyl fluoride functional groups isolated by the process and characterised by a loss of weight at 200° C. lower than 1% as determined by thermogravimetric analysis.
1 . A polymer comprising recurring units derived from at least one ethylenically unsaturated (per)fluorinated monomer (A) containing at least one sulfonyl fluoride group said polymer having a loss of weight at 200° C. lower than 1% as measured by thermogravimetric analysis according to ASTM E1131-86.
2 . The polymer according to claim 1 further comprising recurring units of at least one ethylenically unsaturated (per)fluorinated monomer (B).
3 . The polymer according to claim 1 wherein said monomer (A) is present in an amount such that the equivalent weight of the polymer when converted into its acid form is less than 750 g/eq.
4 . The polymer according to claim 3 wherein the equivalent weight is at least 400 g/eq.
5 . The polymer according claim 1 having a melt flow rate measured according to ASTM D1238-04 at 200° C./5 kg of less than 50 g/10 min.
6 . The polymer according to claim 1 wherein said monomer (A) is CF 2 ═CFOCF 2 CF 2 —SO 2 F and said monomer (B) is tetrafluoroethylene.
7 . Process for the isolation of a polymer of claim 1 from a polymerization latex comprising adding said latex under high shear stirring to an aqueous electrolyte solution held at a temperature equal to or lower than the glass transition temperature of the polymer.
8 . The process of claim 7 wherein the rate of stirring is such that the Reynolds number Re=ρ·N·d I 2 /μ wherein ρ is the density of water (kg/m 3 ), N the number of revolutions per second of the impeller (1/s), d I the diameter of the impeller (m) and μ the dynamic viscosity of water (Pa·s) is greater than 10,000.
9 . The process of claims 7 wherein the electrolyte is selected from the group consisting of HNO 3 , Al(NO 3 ) 3 , Al 2 (SO 4 ) 3 , Ca(NO 3 ) 2 , Zn(NO 3 ) 2 , ZnSO 4 , CaCl 2 , MgSO 4 .
10 . An extruded film comprising the polymer of claim 1 .
11 . A membrane comprising the film of claim 10 in hydrolysed form.
12 . A process for preparing a polymerization latex comprising the polymerization of at least one ethylenically unsaturated (per)fluorinated monomer (A) containing at least one sulfonyl fluoride group in a liquid phase in the presence of a free radical initiator, at least a portion of said free radical initiator being added to the liquid phase held at a temperature T1, said process characterised in that after an incubation time the temperature of the liquid phase is brought to a temperature T2 lower than T1.
13 . The process according to claim 12 wherein the incubation time is at least 5 seconds.
14 . The process according to claim 12 wherein T1 is at least 0° C. and does not exceed 150° C.
15 . The process according to claim 12 wherein T2 is at least 5° C. lower than T1.