| abstract |
Compounds of formula (I) wherein A, C and D represent (1) or (2), B represents (3) or (4) wherein at least one of the substituents is other than hydrogen and also at least one of the phenylene rings may be replaced by a 1,4-phenylene ring in which one or two non-adjacent CH groups have been replaced by nitrogen; k, l, m are 0 or 1, wherein k+l+m must be equal to 1 or 2; Z1, Z2, Z3 each independently of the others represents a single bond, -CH2CH2-, -CH2O-, -OCH2-, -COO-, -OOC-, -CH=CH-COO-, -OOC-CH=CH-, -(CH2)4-, -O(CH2)3-, -(CH2)3O- or -C=C-; R1, R2 represent crosslinkable groups, and S1, S2 represent spacer units. |