Miscible Blends of Cyclic Poly(oxyethylene) in Linear Polystyrene

Cyclic poly(oxyethylene) (POE) was prepared from hydroxyl-terminated linear POE with molecular weights from 400 to 1500 g/mol using a dilute-solution end-coupling route. These cyclic and linear POEs were solution-mixed with linear polystyrene (PS, 15 kg/mol) to prepare binary blends with POE concentrations from 1.5 to 40 wt %. To assess the effect of end groups, PS was also blended with methoxyl-terminated linear POE with molecular weights from 500 to 2000 g/mol. Thermal analysis was conducted using differential scanning calorimetry to measure the glass transitions (T g) in the blends. Using the Fox equation and the blend T g, we estimated the fraction of POE dissolved into the PS. Across the entire concentration and molecular weight ranges studied, cyclic POE exhibited significantly enhanced miscibility compared to the linear POEs. For the smallest POE additives at concentrations ≤10 wt %, completely miscible blends were formed with cyclic POE, partially miscible blends were formed with the methoxyl-terminated linear POE, and the hydroxyl-terminated linear POE was completely immiscible. 1H solid-state NMR spectroscopy was used to examine the POE dynamics and domain sizes in these dynamically asymmetric blends. In the completely miscible blends, the dissolved POE is characterized by typical smallest diameters of 1−1.5 nm and exhibits reduced segmental mobilities compared to pure POE. In the partially miscible blends, two dynamically distinct POE domains are detected, representing the dissolved POE and phase-separated POE. The phase-separated POE exhibits higher segmental mobilities in larger domains (>∼20 nm).