NUCLEOPHILE-INITIATED POLYMERIZATION OF ALPHA,ALPHA-DISUBSTITUTED BETA-LACTONES

The rate constants for reactions of α,α-dialkyl-β-lactones with quaternary ammonium carboxylates in organic solvents were measured. The heat of polymerization of pivalolactone was –20.1 kcal mol-1, allowing calorimetric determination of the rate constants. The rates were much higher in acetonitrile or tetrahydrofuran than in water and correspond to the fastest ring opening polymerizations recorded. Polar substituents in the alkyl groups accelerated the rates, whereas branched alkyls or bridged rings retarded. Pivalate ion was the most reactive nucleophile, followed by acetate, fluoride, and benzoate. Other halide ions and p-toluenesulfonate were extremely slow. Chloropivalolactone reacted with carboxylates to generate chloride ion and an intermediate acyloxypivalolactone, a reaction which can lead to branching. © 1969, American Chemical Society. All rights reserved.