Small and Medium Amplitude Oscillatory Shear Rheology of Model Branched Polystyrene (PS) Melts

Linear and nonlinear rheological properties of model comb polystyrenes (PS) with loosely to densely grafted architectures were measured under small and medium amplitude oscillatory shear (SAOS and MAOS) flow. This comb PS set had the same length of backbone and branches but varied in the number of branches from 3 to 120 branches. Linear viscoelastic properties of the comb PS were compared with the hierarchical model predictions. The model underpredicted zero-shear viscosity and backbone plateau modulus of densely branched comb with 60 or 120 branches because the model does not include the effect of side chain crowding. First- and third-harmonic nonlinearities reflected the hierarchy in the relaxation motion of comb structures. Notably, the low-frequency plateau values of first-harmonic MAOS moduli scaled with M w − 2 (total molecular weight), reflecting dynamic tube dilution (DTD) by relaxed branches. Relative intrinsic nonlinearity Q0 exhibited the difference between comb and bottlebrush via no low-frequency Q0 peak of bottlebrush corresponding to backbone relaxation, which is probably related to the stretched backbone conformation in bottlebrush.

Synthesis of Well-Defined Three-Arm Star-Branched Polystyrene through Arm-First Coupling Approach by Atom Transfer Radical Polymerization

Here we describe a simple route to synthesize three-arm star-branched polystyrene. Atom transfer radical polymerization technique has been utilized to yield branched polystyrene involving Williamson coupling strategy. Initially a linear polymeric chain of predetermined molecular weight has been synthesized which is further end-functionalized into a primary alkyl bromide moiety, a prime requisition for Williamson reaction. The end-functionalized polymer is then coupled using 1,1,1-tris(4-hydroxyphenyl)ethane, a trifunctional core molecule, to give well-defined triple-arm star-branched polystyrene.

Anode Buffer for Organic Devices Composed of Gold Nanoparticles Prepared by Ark Plasma Deposition

Gold nanoparticles (Au NPs) with mean size of 1 nm were placed on an indium tin oxide (ITO) electrode by ark plasma gun. The hole injection at ITO/organic semiconductor was significantly enhanced by the NPs. Though the hole current was unstable upon the voltage scan, it can be substantially stabilized by the insertion of hyper-branched polystyrene (HPS) thin layer between ITO and Au NPs. The work function of ITO electrode was also increased by NPs. The ITO/HPS/Au NPs structure was applied to the anode of an organic solar cell (OSC) with a bulk heterojunction active layer. The power conversion efficiency was significantly higher than that of OSC without anode buffer layer and almost comparable to that with a representative buffer material.