Method of preparing di(ketene acetals)

1. A method for preparing a di(ketene acetal) comprising photoisomerizing a di(vinyl acetal).

2. The method of claim 1 comprising photoisomerizing the di(vinyl acetal) in the presence of a transition metal organometallic compound.

3. The method of claim 2 where the transition metal organometallic compound is an iron organometallic compound.

4. The method of claim 3 where the iron organometallic compound is iron pentacarbonyl.

5. The method of claim 2 where the concentration of the transition metal organometallic compound is 0.001-10.0 mol % based on the di(vinyl acetal).

6. The method of claim 5 where the concentration of the transition metal organometallic compound is 0.01-1.0 mol % based on the di(vinyl acetal).

7. The method of claim 1 comprising photoisomerizing the di(vinyl acetal) in an inert solvent.

8. The method of claim 7 where the inert solvent comprises an alkane.

9. The method of claim 8 where the inert solvent consists essentially of an alkane.

10. The method of claim 8 where the alkane is a C 5 -C 7 alkane or a mixture of such alkanes.

11. The method of claim 1 where the di(vinyl acetal) is a compound of formula I:

where R 1 is hydrogen or a C 1 -C 2 alkyl.

12. The method of claim 11 where the di(vinyl acetal) is 3,9-divinyl-2,4,8,10-tetraoxaspiro[5,5]undecane.

13. The method of claim 1 where the di(vinyl acetal) is a compound of formula II:

where:

R is a bond, —(CH 2 ) a —, or —(CH 2 ) b —O—(CH 2 ) c —; where a is an integer of 1 to 10, and b and c are independently integers of 1 to 5;

R 1 is hydrogen or a C 1 -C 2 alkyl, and

R 2 is hydrogen or a C 1 -C 2 alkyl.

14. The method of claim 13 where the di(vinyl acetal) is di[(5-ethyl-2-vinyl-[1,3]dioxan-5-yl)methyl]ether.

15. The method of claim 1 where the di(vinyl acetal) is a compound of formula III:

where:

R is a bond, —(CH 2 ) a —, or —(CH 2 ) b —O—(CH 2 ) c —; where a is an integer of 1 to 10, and b and c are independently integers of 1 to 5; and

R 1 is hydrogen or a C 1 -C 2 alkyl.