Qing Ge

Hard and soft confinement effects on polymer crystallization in microphase separated cylinder-forming PEO-b-PS/PS blends

Abstract A lamellae-forming poly(ethylene oxide)-b-polystyrene (EOS) has been blended with a polystyrene homopolymer (PS) and a PS oligomer (PSO), respectively, to obtain miscible polymer blends (denoted as EOS/PS-32 and EOS/PSO-32, respectively). Both blends exhibit cylindrical microphase morphologies, with the PEO volume fractions being 0.32. The order–disorder transition temperatures (TODT) of both blends are 175 and 84°C, respectively, as determined by temperature-dependent small angle X-ray scattering experiments. The glass transition temperature of the PS matrix (TgPS) for the EOS/PS-32 blend is 64°C as determined by differential scanning calorimetry (DSC), while that for the EOS/PSO-32 blend is only 16°C. Thus, by controlling the crystallization temperatures (TcPEO), two kinds of nano-confined PEO crystallizations have been achieved in these blends: when TODT≫TgPS>TcPEO in the EOS/PS-32 blend, the PEO-block crystallization is confined under a hard PS confinement, while for TODT>TcPEO≳TgPS in the EOS/PSO-32 blend, the PEO-block crystallization is confined under a soft PS confinement. DSC and wide-angle X-ray experiments show that the crystallizations of the PEO blocks in these two confinement environments behave differently. The PEO-block crystallization kinetics in the hard confinement is much slower than that in the soft confinement. The DSC kinetics studies show that for Tc

Functionalization of Poly(styryllithium) with 1‐Butene Oxide

Functionalization of poly(styryllithium) with 1-butene oxide (BO) was studied in benzene at room temperature. The hydroxyl-functionalized polymer was characterized by size exclusion chromatography (SEC), titration, 1 H NMR, 13 C NMR, DEPT- 13 C NMR (distortionless enhancement by polarization transfer) spectroscopy, MALDI-TOF mass spectrometry and flash column chromatography. The ω-hydroxylated polystyrene was obtained in 99% yield with quantitative regioselectivity (addition to the methylene carbon of 1-butene oxide) to form the secondary alcohol without oligomerization. The amount of unfunctionalized polystyrene formed (<1%) was much less than that found for functionalization with propylene oxide (PO, 6-7%) consistent with reduced proton transfer from the ethyl group in BO versus the corresponding methyl group in PO

Epitaxial Phase Transformation between Cylindrical and Double Gyroid Mesophases

Complex phase transformation between the hexagonal cylinder (Hex) and double gyroid (G) phases in a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer was investigated using two-dimensional (2D) synchrotron small-angle X-ray scattering (SAXS), and transmission electron microscope (TEM). The PS-b-PEO sample contained a small population of another bicontinuous cubic phase having an m Im3 symmetry. These two bicontinuous cubic phases (G and m Im3 ) had the same unit cell dimensions. Under a large-amplitude reciprocating shear, the bicontinuous cubic phases transformed into a “single-crystal”-like Hex phase. When annealed at 150 °C for 40 min, the Hex phase partially transformed into well-oriented twinned structures of the G and m Im3 phases without significant loss of orientation in 2D SAXS measurements. Epitaxial phase transformation relationships between the Hex/G and Hex/ m Im3 phases were identified. The mechanism of the Hex → G transformation was examined by TEM.