Influence of polycarbonate flexibility on the annealing-induced phase separation of the hole transport molecule TPD in a model charge transport composite

The depression of glass transition temperature, annealing-induced phase separation, and morphology were investigated in a binary solid solution of N,N‘-diphenyl-N,N‘-bis(3-methylphenyl)-[1,1‘-biphenyl]-4,4‘-diamine (TPD) in bisphenol A polycarbonate (BPAPC) and cyclohexyl polycarbonate (PCZ) with three different molecular weights. Differential scanning calorimetry, X-ray diffraction, microscopy, and FTIR were used to characterize these composites. Molecularly doped TPD in polymers significantly depressed the Tg of the host polymers. Although it could be expected that the TPD would disperse well in a flexible polymer and cause a substantial decrease in Tg, we find that the extent of depression is more pronounced with the rigid polymer. FTIR studies indicate that a molecular level interaction exists between TPD and the polycarbonates, as shown by the frequency shifts in the aromatic region. Upon annealing, the phase separation and crystallization of TPD lead to a recovery of the Tg of the polymer, by 10−20 ...