abstract |
A compound having formula (I) n nwherein R 1 and R 2 independently represent C 1 -C 6 alkyl; R 3 is C 1 -C 6 alkyl; R 4 is C 1 -C 18 alkyl or C 4 -C 18 heteroalkyl; m is zero, one, two or three; n is one, two or three; and j, k, p, q, r and s independently are zero, one or two; provided that at least one of j, k, p, q, r and s is not zero. |