Isopropenyl isocyanate was shown to have electron-donating properties in free radical copolymerization with the electron-deficient monomer maleic anhydride. Alternating copolymers were obtained over a wide range of composition in the monomer feed. The reactivity ratios were found to be 0.01 or less for each mononer. Formation of a charge transfer complex could be proven by NMR spectroscopy. The alternating behavior is also favored by the very low tendency of both monomers to undergo homopolymerization. Analysis of the configuration of building blocks revealed random incorporation of 2-isocyanatopropene,while maleic anhydride was incorporated preferentially in one diastereomeric sequence, which is in agreement with the formation of a charge transfer complex taking part in the propagation reaction. The new poly(2-propenyl isocyanate-alt-maleic anhydride) [IUPAC name : poly(tetrahydro-2,5-dioxo-3,4-furandiyl)(1-isocyanato-1-methylethylene))] polymers are glassy and the functional groups are stable toward reaction with each other up to approximately 150 degrees C.