Characterizations of hyperbranched polymer thin films

Thermo-mechanical properties in hyperbranched polystyrene (HBPS) films were studied by dynamic mechanical analysis (DMA). The samples for DMA were spin-coated from toluene solutions onto polyimide film (PI) substrates. In case of the proton-terminated HBPS (HBPS-H) film with the thickness of about 400 nm, the α_a-absorption peak corresponding to the segmental motion appeared at a temperature lower than that for the corresponding linear PS film due mainly to the large number density of chain ends. As the HBPS-H film became thinner than about 70 nm, the α_a-absorption peak became broader than that for the thicker one because of the contribution from the free surface and the substrate interface. Moreover, the α_a-relaxation temperature for the HBPS films with dithiocarbamated end groups further decreased, indicating that thermal molecular motion in HBPS films could be controlled by chain end chemistry.