Characterisation of a hyperbranched polyesterin solution

Abstract

The hyperbranched polyester based on poly dimethyl 5-(4 hydroxybutoxy) isophthalate ate has been successfully fractionated and a complete analysis of the solution properties has been carried out. Fractions with an average polydispersity of 1.8 over a range of molecular weight from 5x10(^3) g mol(^-1) were produced starting from an initial polymer with an approximate polydispersity of 7 and average molecular weight of l.3x10(^5) g mol(^-1). A linear analogue of the hyperbranched polyester has been also synthesised and different molecular weight samples were obtained by the use of a transesterification reaction. The hyperbranched fractions were investigated in the dilute regime by size exclusion chromatography, viscometry and light scattering techniques, while the semi-dilute regime has been studied by small-angle neutron scattering. Dilute solution properties in chloroform and in THF have been investigated, whilst D-THF was the solvent for the semi-dilute regime. In the dilute solution regime a whole range of physical parameters have been determined for the hyperbranched fractions and compared, where possible, with the linear analogues. From these results it is concluded that chloroform is a good solvent and THF a poor solvent for the hyperbranched polyester. The molar mass dependence of the radii of gyration has been interpreted by fractal dimension analysis and for the hyperbranched polyester the exponents obtained gave a fractal dimension d(_f)=2.5 ± 0.3 in both the solvents. The exponents obtained by the molar mass dependence of the radius of gyration in the semi-dilute regime have confirmed these values. These exponents also fit with those obtained from analysis of the intermediate g range of the small-angle neutron scattering cross sections, where an average slope 2.5 ± 0.1 was obtained. The values suggested the hyperbranched polymer is a mass fractal object with a rough surface.