A polymer comprising a repeat unit of formula (I): (I) wherein Ar6 and Ar7 each independently represent a substituted or unsubstituted aryl or heteroaryl group; Sp represents a spacer group comprising a chain of at least 2 aliphatic carbon atoms spacing Ar6 from Ar7; m is at least 1; and if m is greater than 1 then —(Ar7)m forms a linear or branched chain of Ar7 groups in which Ar7 in each occurrence may be the same or different.