An initiator for cationic polymerization comprises a salt of a protic acid as well as a protic add. 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 process for cationic copolymerization in the presence of an initiator comprising:
i) feeding a monomer and a base to a mixing appliance, the monomer comprising trioxane;
ii) feeding a protic acid in molar excess, based on the base, to the mixing appliance, wherein the protic acid reacts with the base in i) to form a salt such that excess protic acid is present as well as salt;
iii) polymerizing the monomer in the presence of the initiator that comprises the protic acid and the salt;
wherein the salt comprises the alkali metal or alkaline earth metal salts of protic acids and/or substituted ammonium salts of protic acids, wherein the cations of the ammonium salts have the general formula (I)
where R 1 -R 4 are independently hydrogen, an alkyl group selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, and isobutyl, or an aryl group selected from the group consisting of phenyl and 4-methoxyphenyl.
2. The process according to claim 1 , wherein the process is a continuous process.
3. The process according to claim 1 , wherein the protic acid comprises an inorganic acid selected from the group consisting of sulfuric acid, tetrafluoroboric acid, and perchloric acid and/or an organic sulfonic acid.
4. The process according to claim 3 , wherein the inorganic acid comprises sulfonic acid which comprises fluorinated or chlorinated alkyl or aryl sulfonic acids.
5. The process according to claim 4 , wherein the inorganic acid comprises sulfonic acid, the sulfonic acid being selected from the group consisting of trifluoromethanesulfonic acid, pentafluoroethanesulfonic acid, heptafluoropropanesulfonic acid, nonafluorobutanesulfonic acid, perfluoropentanesulfonic acid, perfluorohexanesulfonic acid and perfluoroheptanesulfonic acid.
6. The process according to claim 1 , wherein the molar ratio of the protic acid to the salt in the initiator is from 1:1 to 1:4.
7. The process according to claim 1 , wherein polymerization is at a pressure from 2 to 60 bar.
8. The process according to claim 1 , wherein the monomers are present from 0.5 to 1% by weight.
9. The process according to claim 1 , wherein the initiator is present in an amount of 10 −6 % to 1% by weight, based on the total weight of the monomers.
10. The process according to claim 1 , wherein the protic acid comprises trifluoromethanesulfonic acid and the salt comprises triethylammonium triflate.
11. The process according to claim 1 , wherein the molar ratio of the protic acid to the salt in the initiator is from 1:0.5 to 1:10.
12. A polyacetal polymer made according to the process defined in claim 1 .
13. The process according to claim 1 , wherein the monomer is combined with a comonomer to form a copolymer, the comonomer comprising a cyclic ether.
14. A polyacetal polymer made according to the process defined in claim 13 .
15. A process as defined in claim 12 , wherein the polyacetal polymer comprises a copolymer.