Rheological characterization of multiarm star copolymers

• Addition of PCL to BH40 increases molar mass and decreases viscosity of copolymer.
• High amounts of PCL change the structure of the copolymer.
• Rheology provides deeper insight into structural changes of thermal process.
• Rheological results strongly coincide with the results of thermal characterization.

Detailed rheological characterization has been performed for star-shaped graft copolymers, prepared from polycaprolactone (PCL) and hyperbranched polyester Boltorn H40 (BH40). As the reactant ratio increased from BH40:PCL = 1:1 to 1:10 the molar mass of the copolymer increased as well. Flow behavior has been determined under destructive shear conditions for the polymer melts at 75 °C, at which Cox–Merz rule has been applied for all the copolymers used. The results show that the addition of PCL to BH40 decreases the viscosity of copolymer with increasing molar mass, but only to the ratio BH40 vs. PCL = 1:4. Above that ratio a slight increase in viscosity is observed for the ratio 1:5, while viscosity significantly increases for the copolymer with the highest reactant ratio. Temperature dependence of viscoelastic properties has been performed in linear viscoelastic range at cooling/heating rate of 10 °C min−1. The results strongly coincides with the results of DSC measurements, moreover, the combination of rheological and thermal characterization provides a deeper insight into structural changes during cooling/heating process.

Figure optionsDownload as PowerPoint slide