Modification with alkyl chains and the influence on thermal and mechanicalproperties of aromatic hyperbranched polyesters

All-aromatic hyperbranchcd polyesters with hydroxy end-groups were function alized with aliphatic n-alkyl carboxylic acids. The length of the n-alkyl c hain as well as the degree of modification were varied and the resulting, p artially amphiphilic polymers were characterized by differential scanning c alorimetry (DSC). With both increasing degree of modification and increasin g length of the alkyl chain the glass transition temperature decreases due to reduced intermolecular hydrogen bonding. When the alkyl chains start to crystallize T-g of the hyper branched polymers increases again. The mechani cal properties of the former brittle hyperbranched polyester were improved by modification with C12 chains and a stable free standing film was obtaine d by compression molding. The film was investigated by means of dynamic mec hanic analysis (DMA) and microscopy, exhibiting a low temperature thermal t ransition and phase separation within the scale of a light microscope. Furt hermore melt rheology measurements were performed on the starting polymer a nd on the C12 modified product. The complex viscosity is reduced strongly b y the modification of the aromatic hyperbranched polyester.