Studies on the synthesis of hydroxyl-terminated isophthalate-based oligoesters via transesterification reaction

A series of isophthalate-based oligoesters was synthesized via the transesterification reaction of dimethyl isophthalate (DI) with various aliphatic diols under different diol(s)/diester molar ratios. The effect of a series of reaction parameters, such as the diols/diester molar ratio, the molar ratio of the diols in the reaction mixture, the species of the diol, the reaction time, the heating procedure, and the species and the amount of the Lewis acid catalyst, on the physical state, the polydispersity, the Mn, the viscosity and the non-volatiles by weight (NVW) of the synthesized oligoesters was studied. A new synthetic procedure for the synthesis of high-solids liquid oligoesters in high yields and high conversions via the transesterification reaction is proposed. The properties of a reference solid oligoester (RefOL) derived from the reaction of DI with the 1,6-hexanediol (HD) (mol ratio DI/HD=1/1.43), were compared to those of a high-solids liquid oligoester (L-311) prepared from the transesterification of DI with a mixture of HD and 2-methyl-1,3-propanediol (MP) (mol ratio DI/HD/MP=1/1.50/1.50). The new high-solids liquid oligoester (L-311) presented more enhanced physical properties than its solid counterpart and owing to its improved processability is expected to be a very promising candidate when used as a binder for the preparation of mar-resistant clearcoats or pigmented coatings.