abstract |
A compound of formula (I): (I) wherein p is at least 1, n is at least 1 and less than or equal to p; Ar is a polycyclic aromatic moiety, R 1 is hydrogen or an optionally substituted hydrocarbyl group and each of R 2 , R 3 and R 4 is independently an optionally substituted hydrocarbyl group, provided that at least one of R 2 , R 3 and R 4 has at least 6 carbon atoms. |