A lamella-forming poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer has been blended with a low molecular weight polystyrene (PS) homopolymer to form a miscible polymer blend. The PEO volume fraction is 0.32, and the order-disorder transition temperature (T ODT) of this blend is 175 °C. Therefore, the PEO blocks form nanocylinders surrounded by a PS matrix below the TODT. Since the glass transition temperature of the PS is 64 °C and the PEO crystal melting occurs at ∼50 °C, the PEO-block crystallization takes place in a two-dimensionally confined glassy environment. The cylinder diameter is determined to be 13.7 nm, based on small-angle X-ray scattering (SAXS) and transmission electron microscopy results. Using simultaneous two-dimensional SAXS and wide-angle X-ray scattering techniques, the crystal orientation (the c-axes of the PEO crystals) within the nanocylinders is found to change simply depending upon the crystallization temperature (T c). At very low Tc (<-30 °C), PEO crystals are randomly oriented within the confined cylinders. Starting at Tc ) -30 °C, the crystal orientation changes to be inclined with respect to the cylinder axis, a ˆ. The tilt angle from a ˆcontinuously increases with increasing Tc, and finally it becomes 90°when Tc g 2 °C. Crystallographic analysis indicates that the crystal c-axis orientation at each Tc corresponds to a uniform crystal orientation.

We proposed an approach to precisely control the density of tethered chains on solid substrates using PEO-b-PS and PLLA-b-PS. As the crystallization temperature Tx increased, the PEO or PLLA lamellar crystal thickness d(L) increased as well as the reduced tethering density sigma; of the PS chains. The onset of tethered PS chains overcrowding in solution occurs at sigma(*) approximately 3.7-3.8 as evidenced by an abrupt change in the slope between (d(L))(-1) and Tx. This results from the extra surface free energy created by the tethered chain that starts to affect the growth barrier of the crystalline blocks.

A series of poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymers were designed and synthesized to study the change in crystal orientation of PEO blocks under different confinement sizes. The volume fraction of PEO blocks (f PEO) in these copolymers was kept almost identical (the f PEO values were between 0.45 and 0.48) but with different number-average molecular weights for the PS and PEO blocks (M̄ n PEO and M̄ n PS). Therefore, the phase morphology of these copolymers was a lamellar structure with different PEO and PS layer thicknesses (d PEO and d PS) detected by synchrotron small-angle X-ray scattering (SAXS) experiments. Since the melting temperature of these PEO crystals is lower than the glass transition temperature of the PS layers, the PEO block crystals could be melted and recrystallized under one-dimensional (1D) confinement at different crystallization temperatures (T c). The PEO block crystal orientation changes were monitored using synchrotron wide-angle X-ray diffraction (WAXD) experiments. It was found that the crystalline PEO chain orientation (the c-axis in the crystals) underwent a change from being perpendicular (homogeneous) to the layer normal direction (n̂) at low T cs to parallel (homeotropic) at high T cs in these 1D confined samples with the d PEO ranging from 8.8 to 23.3 nm. However, with the gradual release of this 1D confinement, i.e., increasing the d PEO, a broad T c region in which the inclined c-axis orientation was originally observed in the PEO-b-PS with the low M̄ n PEO (8.7K g/mol) and M̄ n PS (9.2K g/mol) became increasingly narrowed by pushing the starting T c where the tilting initiates toward higher T c and reducing the ending T c where the parallel orientation of the c-axis with n̂ starts. In the PEO-b-PS sample with the highest M̄ n PEO (57K g/mol) and M̄ n PS (61.3K g/mol) in this study, this T c region was narrowed to less than 5 °C, suggesting the confinement size effect on the crystal orientation of the PEO crystals. The homogeneous to homeotropic orientation change of the c-axis in the PEO crystals with increasing T c was explained to be largely governed by the primary nucleation and crystal growth processes of the PEO blocks for developing the maximum crystallinity. A semiquantitative calculation was attempted to illustrate why the homogeneous orientation of the PEO crystals takes place in the 1D confinement based on the SAXS, WAXD, and differential scanning calorimetric results. It was expected that when the d PEO becomes large enough, the homogeneous orientation of the c-axis in the PEO crystals would disappear.

A series of poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymers were used to generate nucleation sites for the crystal growth of a homo-PEO fraction in solution. The numberaverage molecular weights of the PEO blocks (M n PEO ) were similar, and the number-average molecular weights of the PS blocks (Mn PS ) ranged from 4.6K to 17K g/mol. In PEO-b-PS/(chlorobenzene/octane) solutions, square-shaped single crystals bounded by four {120} planes were isothermally grown and observed with transmission electron and atomic force microscopy. A "sandwich" lamellar structure, constructed by a PEO single crystal layer covered by two tethered PS block layers on the top and bottom crystal basal surfaces, was found. These diblock copolymer single crystals were used as seeds to grow homo-PEO (M n PEO ) 56K g/mol) single crystals in amyl acetate. When the Mn PS in the block copolymer was 4.6K g/mol, the edges and corners of the {120} bounded PEO-b-PS single crystals served as nucleation sites to initiate the further growth of the homo-PEO single crystal. As the Mn PS of the block copolymers increased, the homo-PEO crystal growth was increasingly hampered along the {120} edges of the PEOb-PS single crystals. When the Mn PS of the block copolymer was 17K g/mol, only the four corners of the PEO-b-PS single crystal could still act as nucleation sites. The four edges were chemically "shielded" by the tethered PS blocks. This indicates that increasing the Mn PS led to a higher reduced tethering density of the PS blocks on both the basal surfaces of the PEO-b-PS single crystals. The repulsion generated among the tethered PS blocks caused the PS blocks located near and at the edges to advance along the [120] direction. Interestingly, this local environment only accepted the PEO-b-PS molecules but rejected the homo-PEO molecules from further growth. As a direct result of this study, novel channel-wire arrays on a submicrometer length scale having chemical and geometric recognitions could be fabricated via alternating crystal growth of PEO-b-PS and homo-PEO. This fabrication provided robustly controlled arrays with spacing down to 50 nm.

Halogen-free flame-retarded polyethylene materials have been prepared by using magnesium hydroxide (MH) as a flame retardant combined with red phosphorous (RP) and expandable graphite (EG) as synergists. The effects of these additives on the combustion behavior of the filled linear low density polyethylene (LLDPE), such as a limiting oxygen index (LOI), the rate of heat release (RHR), the specific extinction area (SEA), etc., have been studied by the LOI determination and the cone calorimeter test. The results show that RP and EG are good synergists for improving the flame retardancy of LLDPE/MH formulations. In addition, a suitable amount of ethylene and vinyl acetate copolymer (EVA) added in the formulations can increase the LOI values while promoting the char formation and showing almost no effect on the RHR and SEA values.

Small angle x-ray analyses show that the shear-induced hexagonal perforated layer phase in a poly(ethylene oxide)- b-polystyrene diblock copolymer consists of trigonal (R3;m) twins and a hexagonal (P6(3)/mmc) structure, with trigonal twins being majority components. Transmission electron microscopy reveals that the hexagonal structure is generated through sequential intrinsic stacking faults on the second layer from a previous edge dislocation line, while the trigonal twins are formed by successive intrinsic stacking faults on neighboring layers due to the plastic deformation under mechanical shear.

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Nanoscale tailored polymer crystalline morphology is studied in a polystyrene-b-poly-(ethylene oxide) (PS-b-PEO) diblock copolymer with number-average molecular weights for the PS and PEO blocks being 17 000 and 11 000 g/mol, respectively. The PEO volume fraction is 0.39. After large amplitude planar reciprocating shear, a hexagonally perforated layer (HPL) structure is obtained. Since the glass transition temperature of the PS blocks (72 °C) is higher than the PEO crystal melting temperature (∼51 °C when the crystallization temperature, T c, is lower than 40 °C), the PEO block crystallization is confined within the HPL structure. The PEO crystal (the c axis) orientation within this complex confined environment is investigated using simultaneous synchrotron two-dimensional smallangle and wide-angle X-ray scattering (SAXS and WAXS) methods. The PEO crystal orientations with respect to the layer plane (or the {000l}) of the HPL structure have been found to be dependent upon T c. At very low Tcs (below -50 °C), the PEO crystals have a random orientation. Between -50 °C e Tc e -10 °C, the PEO crystal c axes preferentially orient parallel to the layer plane. Above Tc ) 0 °C, the crystal c axes orient inclined to the layer plane of the HPL structure, and the tilt angle with respect to the layer plane increases with Tc. Contrary to the confined polymer crystallization in nanolamellar structure, however, the c axis orientation perpendicular to the layer plane is not found at least up to Tc ) 40 °C in this HPL confined environment. Meanwhile, the ribbonlike PEO crystal growth is specifically tailored along the {101 h0} planes of the hexagonal PS perforations. Apparent crystallite size analyses using the Scherrer equation confirm the one-dimensional crystal growth at high Tcs. Using time-resolved WAXS experiments, the crystal orientation is observed to occur in the early stage of crystallization with a crystallinity of ∼7 wt %. Based on the results of specifically designed self-seeding experiment, the crystal orientation is determined by the crystal growth (surface nucleation) in the confined HPL phase rather than the preorientation of primary nuclei.