A study on biodegradable aliphatic poly(tetramethylene succinate): the catalyst dependences of polyester syntheses and their thermal stabilities

Abstract

In this study, titanium alkoxide catalyst dependences of condensation polymerization, thermal degradation and stability were examined for a biodegradable aliphatic poly(tetramethylene succinate) (PTMS). A series of aliphatic PTMSs were synthesized through polycondensation of 1,4-butanediol and succinic acid in bulk with various amounts of titanium tetraisopropoxide (TTiPO) as the catalyst, and were further characterized by gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. To reveal the presence and effect of catalyst residues, the crude product PTMS samples were precipitated in methanol from their chloroform solution, and were further refluxed in an acid solution to selectively hydrolyse the weak metal alkoxide moieties formed. Results of GPC analysis indicated that the original precipitated polyesters exhibited remarkably increasing molecular weights with a decrease in the catalyst/succinic acid feed molar ratio, and strong catalyst dependence of molecular weight and distribution were detected for the product polyesters. As for the acid deactivated samples, it was found that the higher the catalyst concentration used for polyester synthesis, the more remarkable was the decrease in molecular weight observed as compared with the corresponding original precipitated polyesters. Hence, a weak chain linker structure, such as (RO) n Ti(OP) m with m> 1 was reasonably suggested to be included in the macromolecular architecture of polyester, where RO and P respectively express the alkoxyl moiety and polyester chain. Thermal analysis showed similar melting points and glass transition temperatures for all polyester samples. In contrast, a strong catalyst dependence of thermal degradation and stability was found for the TTiPO catalysed polyesters, and can be interpreted for the formed weak (RO) n Ti(OP) m structures.