Influence of the Activity of Transesterification Catalysts on the Phase Behavior of PC-PET Blends

Samples of PC/PET blends, prepared by reactive blending in the presence of different catalysts, were analyzed by 1H NMR and DSC, in order to evidence the effects of the transesterification reactions on the molecular structure and thermal properties. The 1H NMR analysis evidences the formation of copolymers whose degree of randomness increases with the mixing time. The thermal analysis shows that the melting peak, due to the crystalline phase of PET, tends to disappear with increasing mixing time and, then, with decreasing block length in the PC-PET copolymers. At the same time, the two amorphous phases (PET and PC rich phases), characterized by two glass transitions, tend to originate only one glass transition which is observed when the block length is 15 monomeric units or lower. This copolymer structure is reached rapidly in the presence of catalysts based on titanium and samarium, at intermediate times for catalysts based on europium, cerium, calcium/antimony, erbium and does not occur at all with terbium catalyst.