Nineteen oxybutylene/oxyethylene/oxybutylene triblock copolymers [Bn/2EmBn/2, E ) oxyethylene, OCH2CH2; B ) oxybutylene, OCH2CH(CH2CH3)] were prepared and characterized. Twelve of the copolymers microphase-separated in the melt. Investigation of this microphase-separation behavior using small-angle X-ray scattering (SAXS) yielded values of the domain spacing (d-spacings) in the ordered phases and of the temperature of the order-disorder transition (TODT). In several cases the ordered phase structure was deduced from a combination of 1D and 2D SAXS and rheology. Values of TODT for the triblock copolymers were ca. 100 °C lower than those for EmBn diblock copolymers of identical composition and chain length but 30 °C higher if compared with diblock copolymers of half the triblock length. Values of the d-spacings indicated that the triblock copolymers were 10% more stretched than corresponding diblock copolymers. Determination of the Flory-Huggins parameter (χ) for the diblock and triblock systems gave identical results. The experimental results are compared with the prediction of mean-field theory.

Three poly(oxyethylene-block-oxybutylene) diblock copolymers, E76B38, E114B56, and E155B76, were blended with poly(oxybutylene) homopolymer, B14 and B28, such that lamellae (lam), gyroid (gyr), hexagonally packed cylinders (hex), and body-centered-cubic (bcc) spheres were obtained in the melt. The nonisothermal crystallization on cooling of the blends was investigated with synchrotron smallangle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). In general, two classes of behavior are observed. In confined crystallization the morphology of the melt is retained, and crystals have limited dimensions. In breakout crystallization the melt morphology is destroyed, and a new lamellar morphology is formed. The morphological state (confinement in or breakout of melt morphology) during crystallization was evaluated by the change of the position of the first-order peak (q*) in SAXS and the crystallization temperature (T c). Breakout of morphology was observed in all E76B38/B14 blends and E114B56/ B28 and E155B76/B28 blends with lam morphology, while confined crystallization occurred in E155B76/B28 blends with hex and bcc morphologies and E114B56/B28 blends with bcc morphology. Confined crystallization was also observed in low E content E114B56/B28 blends with hex morphology. These findings lead to two conclusions: (i) the tendency of confined crystallization varies with morphology and decreases in the order bcc > hex > lam, and (ii) confinement on crystallization tends to increase with the extent of segregation between the two blocks. The DSC results show that the crystallization temperature of the blends varies with morphology and chain length of the block copolymers. A much lower T c was observed for the blends exhibiting confined crystallization behavior, and this phenomenon is explained by a homogeneous nucleation mechanism. The morphology over a larger scale was also examined by polarized light microscopy, and spherulite formation was only observed in the blends where the morphology was easily broken out during crystallization.

Twenty-six poly(oxyethylene)-poly(oxybutylene) diblock copolymers were prepared by anionic polymerization. The phase behavior of these copolymers was studied near the order−disorder transition over the composition range from 0.21 to 0.84 poly(oxyethylene) volume fraction. Small-angle X-ray scattering was used to characterize phase transition temperatures and ordered state symmetries. Four distinct microstructures were observed:  body-centered cubic, hexagonally packed cylinders (hex), lamellae (lam), and a bicontinuous cubic phase with Ia3̄d symmetry, together with a less well-defined region of the phase diagram comprising either hexagonally perforated layers or biphasic hex and lam. The Flory−Huggins parameter as a function of temperature was estimated using both the mean-field approximation and a fluctuation correction to the mean-field theory. The experimental microphase behavior is compared with the exact mean-field phase diagram calculated using self-consistent-field theory.

The crystallization of shear oriented oxyethylene/oxybutylene ͑E/B͒ diblock copolymers has been studied by simultaneous small and wide angle x-ray scattering. Crystallization of ordered melts can be accompanied by a change in length scale and retention of the melt orientation. Lamellar melts crystallize with an increase in length scale with multiply folded E blocks and the B blocks slightly stretched from their melt conformation. Crystallization from oriented gyroid melts leads to an increase in length scale with preferred melt directions being selected. The retention of layer planes on crystallization from an ordered melt is caused by the local stretching of chains and the locally one-dimensional structure, despite the relative strength of the structural process. We demonstrate that an interfacial preordering effect can cause crystallographic register to jump length scales in a soft matter system showing epitaxial crystallization.

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EBE and BEB triblock copolymers were prepared and characterized. Microphase separation in the melt state was studied, and the results combined with those for EB and BEB copolymers reported previously. The microphase separation temperature (MST) was determined from the temperature dependence of SAXS. There was a large difference in MST between the diblock and triblock copolymers as expected from theory. The Flory‐Huggins parameter (χ) was independent of block architecture for all three series provided that the E block lengths in the EBE copolymers exceeded 65.

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