A method of preparing a polymeric transport system, comprising a) reacting a compound of Formula (IXa) ##STR32## with a compound of Formula (X) ##STR33## wherein: Y1-2 are independently O or S;M is selected from either X or Q; wherein X is an electron withdrawing group and Q is a moiety containing a free electron pair positioned three to six atoms from C(???Y2); R2-5 are independently selected fro