Patent ID: 7105689

Claim:
A compound of formula (I): L 1 -X-L 2 (I) in which X is a lower alkylene group, an arylene group or an alkarylene group; L 1 is in which Y 1 is oxygen, sulfur or N—R 17 , R 12 , R 14 , R 15 , R 16 and R 17 independently of one another being hydrogen, alkyl or aryl; and R 11 and R 13 independently of one another being alkyl or ayrl, L 2 is in which Y 2 is oxygen, sulfur or N—R 27 , R 22 , R 24 , R 25 , R 26 and R 27 independently of one another being hydrogen, alkyl or aryl, R 21 and R 23 independently of one another being alkyl or aryl, it being possible for L 1 and L 2 to be identical or different.