Sulfonium initiators, process for production and use in cationic polymerizable compositions

1. An initiator comprising at least one structural element characterized by the following formula:

wherein

X − is a non or low coordinating anion, R1, R2, R3, R4 are each independently selected from the group consisting of linear, cyclic or branched C 1 -C 20 alkyl or alkylene groups, wherein one or more of the methylene groups contained in the alkyl or alkylene group can be substituted by —CO—, —CONH—, —CON(CH 3 )—, —S— and/or —O—, and wherein R1, R2, R3 and/or R4 can act as a bridging element connecting two or more structural elements,

2. The initiator according to claim 1 having a molecular weight in the range of about 250 to about 25,000 g/mol, wherein the molecular weight is expressed by MW for monomers and Mn (number average molecular weight) for oligomers and/or polymers.

3. The initiator according to claim 1 with a sulfonium equivalent weight Eq in the range of about 300 to about 800 g/mol, wherein Eq is determined as molecular mass of the initiator divided by number of sulfonium groups present in the initiator.

4. The initiator according to claim 1 , wherein X − is selected from the group consisting of BF 4 − , CF 3 SO 3 − , SbF 6 − , AsF 6 − or 2,5-di-chloro-benzolsulfonate.

5. The initiator according to claim 1 , wherein

R1 and R2 are each independently from the group consisting of methyl, ethyl, n-propyl, 2-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl or n-octyl and wherein one or more methylene groups of R1 and R2 can be substituted by —CO—, —CONH—, —CON(CH 3 )—, —S— and/or —O—,

R3 is methyl, ethyl, n-propyl, 2-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl or n-octyl,

R4 is R3, n-nonyl, n-decyl, n-undecyl or n-dodecyl, wherein one or more of the methylene groups of this alkyl chain can be substituted by —CO—, —CONH—, —CON(CH 3 )—, —S— and/or —O—.

6. A curable composition comprising:

(A) at least one cationic polymerizable compound as component (A),

(B) at least one initiator as described in claim 1 as component (B),

(C) optionally a filler as component (C), and

(D) optionally other additives as component (D).

7. The curable composition according to claim 6 , wherein the cationic polymerizable compound contains aziridine groups.

8. The curable composition according to claim 7 , wherein components (A) to (D) are contained in the following amounts:

Component (A): about 10 wt.-% to about 90 wt.-%

Component (B): about 1 wt.-% to about 30 wt.-%

Component (C): about 0 wt.-% to about 80 wt.-%

Component (D): about 0 wt.-% to about 89 wt.-%.

9. The curable composition according to claim 8 having at least one of the following properties:

A shore A hardness (DIN 53505, measured 24 h after mixing) above about 40 to 80;

A tensile strength according to DIN EN 53504, (MPa) above about 0.4; and/or

An elongation at break according to DIN EN 53504 (%) above about 50.

10. A process of producing a curable composition, the process comprising the steps of:

providing at least one cationic polymerizable compound as component (A), and at

least one initiator as described in claim 1 as component (B),

mixing components (A) and (B),

11. A method of curing a cationically polymerizable substance, comprising the step of adding an initiator as described in claim 1 to start the curing process of a cationic polymerizable substance.

12. The curable composition of claim 7 , wherein the composition is a coating, sealing, moulding, adhering, or material impression.

13. The curable composition of claim 7 , wherein the composition is a dental material selected from the group consisting of precision impression materials, situation impression materials, bite registration materials, duplicating materials, and modelling materials.