Facile and solvent-free synthesis of a novel bio-based hyperbranched polyester with excellent low-temperature flexibility and thermal stability

Abstract In this work, a novel biobased hyperbranched polyester (HBPE) with excellent low-temperature flexibility (low Tg) and thermal stability, was prepared from the self-polycondensation of AB2 monomer based on methyl ricinoleate (MR), a commercially available derivative from castor oil. The AB2 monomer was facilely synthesized by UV-initiated thiol-ene addition between MR and 2-mercaptoethanol in the absence of solvents. The reaction parameters were systematically optimized, and the highest yield up to 98 % was achieved with almost complete conversion of double bond within 2 h. A series of HBPEs were then obtained via bulk polymerization of the AB2 monomer under different conditions. Among the four transesterification catalysts investigated, Ti(OBu)4 was demonstrated to be the most efficient one due to the higher polymerization efficiency and molecular weight (Mn = 13,000∼17,000 g/mol) of as-obtained HBPEs. And the degree of branching (DB) was estimated to be in the range of 0.30∼0.42. Notably, the HBPEs with dangling chains exhibited a low glass transition temperature (Tg) of ―42.8∼―59.2 °C, indicative of excellent low-temperature flexibility. TGA results indicated that the onset thermal degradation temperature under nitrogen exceeded 310 °C for all the HBPEs. In comparison to the polyrincinoleate as a linear polyester analogue, the HBPE behaved like Newtonian fluid behaviors with lower complex viscosities.