An initiator for cationic polymerization comprises a salt of a protic acid as well as a protic acid. The molar ratio of protic acid to salt is in the range from 1:0.01 to 1:2000. The initiator is used for example for cationic homo- or copolymerization of trioxane, and permits stable and flexible operation of the polymerization.
1. A composition for cationic polymerization comprising:
an initiator comprising at least one protic acid and at least one salt of a protic acid, wherein said at least one protic acid is sulfuric acid, tetrafluoroboric acid, perchioric acid, fluorinated alkyl sulfonic acid, chlorinated alkyl sulfonic acid or aryl sulfonic acid, and wherein said salt of protic acid is an alkali metal or alkaline earth metal salt of protic acid and/or a substituted ammonium salt of protic acid, the cations of the ammonium salt having the general formula (I)
where R 1 -R 4 are independently hydrogen, an alkyl group or an aryl group; and
at least one monomer comprising trioxane.
2. The composition according to claim 1 , wherein the organic sulfonic acid is trifluoromethanesulfonic acid, pentafluoroethanesulfonic acid, heptafluoropropanesulfonic acid, nonafluorobutanesulfonic acid, perfluoropentanesulfonic acid, perfluorohexanesulfonic acid or perfluoroheptanesulfonic acid.
3. The composition according to claim 1 , wherein where R 1 -R 4 are independently hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or 4-methoxyphenyl.
4. The composition according to claim 1 , wherein the molar ratio of protic acid to salt is in the range from 1:0.01 to 1:2000.
5. The composition according to claim 1 , wherein the molar ratio of protic acid to salt is in the range from 1:0.5 to 1:10.
6. The composition according to claim 1 , wherein the molar ratio of protic acid to salt is in the range from 1:0.8 to 1:8.
7. The composition according to claim 1 , wherein the molar ratio of protic acid to salt is in the range from 1:1 to 1:4.
8. The composition according to claim 1 , in an amount of 10 −6 % by weight to 1% by weight, based on the total weight of monomers used.
9. The composition according to claim 1 , wherein the composition includes a mixture of monomers.
10. The composition according to claim 9 , wherein trioxane is present in the monomer mixture in the range of from 0.1% to 25% by weight based on the weight of the total mixture.
11. The composition according to claim 1 , wherein the composition produces a polyacetal polymer.