Stabilization modification and thermal degradation behaviors of hydroxyl-terminated hyperbranched polyesters

A series of hydroxyl-terminated hyperbranched polyesters with 1, 1, 1-trimethylolpropane as the core and 2, 2-bis(hydroxymethyl)propionic acid as the AB2-monomer were end-capped with long-chain n-alkyl carboxylic acids. The modification degree of hyperbranched polyesters was confirmed by titration of hydroxyl values and proton nuclear magnetic resonance (1H-NMR). The influence of generation number, end-group type, and degree of modification on thermal stability and thermal degradation behavior of hyperbranched polyesters was investigated by thermogravimetric-derivative thermogravimetric analysis (TG-DTG). The results show that the thermal stability of hyperbranched polyesters is highly improved after modification. The increase of modification degree or the shortening in the alkane chain length of the end groups enhances the thermal stability of hyperbranched polyesters. The decomposition process of hyperbranched polyesters is composed of two stages, i. e. damage of the shell (composed of numerous end groups) and collapse of the sheleton (core" composed of lots of C-C single bonds). This study indicates that the first weightlessness peak becomes negligible with the decrease of polar hydroxyl-terminated groups or with the increase of nonpolar alkyl-terminated groups."