Rubbery polyhydroxyesters based on polyethylene glycol diglycidyl ether: reaction and vitrimer-like behavior catalyzed by tin octoate

Abstract

Polyhydroxyesters prepared from epoxy and organic acids are vitrimers that can rearrange their topology from exchange reactions enhanced by catalysts, forming crosslinked networks which can be deformed and remolded. In this work, the curing kinetic and thermal properties of polyhydroxyesters vitrimers based on polyethylene glycol diglycidyl ether (PEGDGE), citric acid (CA) and sebacic acid (SA) in presence and absence of tin octoate (Sn(Oct)2) were investigated. Differential scanning calorimetry (DSC) non-isothermal experiments and Ozawa models were used for the curing kinetic studies and thermogravimetry analysis (TGA) and thermomechanical analyses (TMA) employed to investigate the thermal behavior of the networks. The highest curing enthalpy of these exothermic reactions was observed in the binary system PEGDGE:CA without catalyst (326 J/g). Addition of Sn increases the reaction enthalpy for formulations with SA and decreases for formulations rich in CA. The lowest activation energy was shown for the formulation PEGDGE:CA = 3:2 containing 1 mol% of Sn (56 kJ/mol). The polyhydroxyesters presented Tg ranging from -24 to -48 °C, and the Tg decreases when the proportion of SA was increased in the formulation. The thermal stability was increased when the SA content increased and was decreased when the content of Sn increased from 1 to 5 mol%. Esterification of PEGDGE and organic acids (SA and CA) occurs even in the absence of catalyst, producing rubbery polyesters, but the use of Sn(Oct)2 decreases the curing time. Ternary networks of polyhydroxyesters containing Sn showed a discontinuity in the thermal expansion around 180°C attributed to exchange reactions, similarly to theorized for this class of vitrimer material.