Tetrakis(triphenyl phosphite)nickel(0)+ maleic anhydride: ligand exchange and free-radical formation
Tetrakis(triphenyl phosphite)nickel(0)(Ni(tp)4) reacts reversibly with maleic anhydride (man) in methyl methacrylate (mma) or styrene (st) solution to form the species Ni(tp)2(man)(III). Kinetic studies based on absorbance measurements are consistent with a rate-determining dissociation of Ni(tp)4; the intermediate compound Ni(tp)3(man)(formed by complexing of Ni(tp)3 and man) reacts by an SN1 process to generate the final product(III). The equilibrium constant for the overall ligand exchange has been evaluated.
Reaction between Ni(tp)3 and man generates free-radicals capable of initiating the copolymerization of man and mma or st; the efficiency is extremely low on account of the predominance of competitive ligand exchange reactions. The copolymerization has been studied over a range of conditions and rates of initiation have been calculated by a method that does not involve a knowledge of the monomer reactivity ratios.
The kinetics of both ligand exchange and initiation reactions have been examined and there is satisfactory agreement with experiment under a variety of conditions.