The lattice disordering transition (LDT) and the domain dissolution transition (DDT) of a highly asymmetric polystyrene-block-poly(ethylene-co-but-1-ene)-block-polystyrene (SEBS-8) triblock copolymer with a volume fraction of polystyrene (PS) block of 0.084 have been investigated by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and rheology. The PS spheres formed in the SEBS-8 sample exhibited a body-centered cubic (bcc) lattice at lower temperatures and underwent disordering in the bcc lattice (so-called LDT) at ∼150 °C. Above this temperature (T LDT), spheres in liquidlike short-range order (LSO) with relatively thin interface between the PS domain and the poly(ethylene-co-but-1-ene) (PEB) matrix were detected up to ∼210 °C, above which the spherical domains started to dissolve into the PEB matrix. Finally, the spherical domains were completely dissolved into a homogeneous state at ∼232 °C. The starting and the final dissolution temperatures are referred to as the T DDT and the order-to-disorder transition temperature (T ODT). The LDT was verified by the SAXS results that the higher order diffraction peaks from the bcc lattice disappeared above the T LDT, while particle scattering of spheres due to the intraparticle interference as well as the interparticle interference of spheres in LSO was clearly observed between the T LDT and the T DDT. The spheres in LSO were further elucidated by rheology and TEM observation. It was found that a precipitous decrease in storage modulus (G‘) and a dramatic change in the Bragg spacing occurred at the same temperature of the T LDT. It was also observed that the slope in the plots of G‘ versus frequency (ω) and that in the plots of loss modulus (G‘ ‘) versus ω in the terminal region were two and one, respectively, at temperatures above the T LDT. This is attributed to the fact that because of the absence of the bcc lattice in long-range order, spheres in LSO do not contribute significantly to the shear moduli in the terminal region. Therefore, even if the terminal behavior observed generally for a homogeneous mixture (namely the slopes in the plots of G‘ versus ω and G‘ ‘ versus ω are two and one) is exhibited at a temperature, this temperature is not necessarily above the T ODT. The characteristic domain spacing in LSO did not change much with temperature, but it increased between the T DDT and the T ODT due to the dissolution of spheres.

We report an experimental result for a lamellar orientation in cross-linked polystyreneblock-polybutadiene-block-polystyrene (SBS) triblock copolymer that was uniaxially drawn at 130 °C (above the glass transition temperature of polystyrene; T g(PS)). The lamellar orientation was examined using two-dimensional small-angle X-ray scattering (2d-SAXS) experiments. It was revealed that the lamellar normal preferentially oriented perpendicular to the stretching direction such that the microdomain interface between polystyrene and polybutadiene lamellae is more or less parallel to the stretching direction, where the lamellar normal denotes the direction normal to the lamellar interface. On the other hand, a herringbone structure was induced by the uniaxial stretching for a sample drawn at room temperature (below T g(PS)) without the lamellar orientation. Therefore, it is concluded that the straininduced orientation of lamellae can be only attained above Tg(PS) and that the uniaxial stretching above Tg(PS) was found to be an effective way to induce the preferential orientation of lamellae. The lamellar orientation was found to be improved by the thermal annealing at a stretched state and more by increasing the extent of the stretching, as well as cross-linking density.

The kinetics and mechanism of morphological transition from nonequilibrium lamella to cylinder microdomain in a polystyrene-block-poly(ethylene-co-but-1-ene)-block-polystyrene (SEBS) triblock copolymer were studied by using time-resolved synchrotron small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and rheology. The sample cast from toluene solution formed a nonequilibrium morphology of the alternating lamellae (LAM) of polystyrene (PS) and poly(ethylene-co-but-1-ene) (PEB) blocks because toluene is a good solvent for PS chains but a poor solvent for PEB chains. LAM of PS and PEB blocks was transformed into the hexagonally close packing (HEX) of PS cylinders in PEB matrix when the as-cast sample was annealed above 140 °C, which is above the glass transition temperature of the PS block. From the time-resolved SAXS and TEM, the coexistence of the LAM and HEX microdomains was clearly confirmed during the entire process of the order-to-order transition (OOT) from LAM to HEX, and the lamellar fraction in the coexisting phase decreased with increase of the annealing time. It was also found that the storage modulus during the transition linearly decreased with the lamellar fraction. The temporal change in the LAM fraction in the coexisting phase was fitted by the Avrami-type exponential decay function. The mechanism of the OOT was discussed on the basis of the evaluated Avrami exponent (n). We found that the value of n was ∼1 at higher annealing temperatures (above 160 °C), whereas it was ∼0.5 at lower annealing temperatures. Thus, it is concluded that at higher temperatures the nucleation and growth of the HEX microdomains from LAM phase result from both interlayer correlation of the modulation and in-layer modulation of LAM layers (2-dimensional growth). On the other hand, at lower temperatures, one-dimensional growth from the in-layer modulation induced the nucleation and growth of HEX microdomains.