This paper describes the free radical terpolymerization of maleic anhydride (MSA), trans-anethole (ANE) and vinyl-iso-butylether (VIBE) in chloroform, acetonitrile and tetrachloromethane at 60 degreesC with a,alpha,alpha(1)-azoisobutyronitrile as initiator. All these monomers are non-homopolymerizable under the used conditions, and the binary copolymerizations take place only between MSA and one of the donor monomers but not between the two donor-monomers ANE and VIBE. Their reactivity ratios in the binary copolymerizations are all close to zero. The terpolymerizations result in polymers with always about 50 mol% donor- and 50 mol% acceptor monomer units. Against the common MSA-macroradical, VIBE is a little more reactive than ANE in acetonitrile and in chloroform; but in tetrachloromethane ANE is incorporated into the polymers 1.4 times faster than VIBE at the same concentration. The charge transfer complexes between MSA and two donor monomers have only small equilibrium constants and therefore low concentrations in the monomer feeds. But these complexes are more reactive than the free monomers. Their contribution to the total polymerization rate was kinetically determined for the two binary copolymerizations between MSA and one of the two donor monomers in chloroform. At low monomer concentrations the free monomers dominate the overall polymerization rate. At high monomer concentrations the charge transfer complex participates more to the polymerization process. (C) 2003 Elsevier Ltd. All rights reserved.