Lactone polymers. IV. Glass transition temperatures of monomeric lactones and their polymers

Glass transition temperatures were determined for a homologous series of unsubstituted lactone monomers varying in ring size from four to sixteen atoms. Examination of these transitions as a function of ring size shows a maximum in T g for the seven‐atom ε‐caproalctone ring. This behavior is interpreted on the basis of a conformational change in lactones which occurs in rings containing seven to nine atoms. The T g values of polylactones derived from these cyclic esters were determined and correlated with T g values of the monomers. Except for the anomolous ε‐caprolactone and the strained fourmembered lactone, an apparently constant difference between monomer and polymer T g is observed. Treatment of the polylactones as methylene copolymers permits extrapolations of the T g values to obtain that of polyethylene. Two values suggesting the γ and β transitions of polyethylene are obtained.