We investigated the order−order transition (OOT) and the order−disorder transition (ODT) in a polystyrene-block-polyisoprene-block-polystyrene copolymer (Vector 4111, Dexco Polymers Co.), which has a weight-average molecular weight of 1.4 × 105 and a 0.183 weight fraction of polystyrene (PS) blocks, using small-angle X-ray scattering (SAXS) and rheological measurements. Specifically, SAXS experiments reveal that Vector 4111 undergoes an OOT at 179−185 °C with (i) hexagonally-packed cylindrical microdomains of PS at T ≤ 179 °C, (ii) the coexistence of cylindrical and spherical microdomains of PS at 180 °C ≤ T ≤ 185 °C, and (iii) spherical microdomains of PS in a cubic lattice at 185 °C < T ≤ 210 °C, and (iv) the cubic lattice of the spheres is distorted with a further increase of temperature so that the lattice disordering transition occurs at temperatures between 210 (onset) and 214 °C (completion) and the spherical microdomain structure of PS with a liquidlike short-range order persists even up to 220 °C, the highest experimental temperature employed. The SAXS results are confirmed by independent rheological measurements. Transmission electron microscopy (TEM) was employed to investigate the microdomain structures of Vector 4111 at elevated temperatures by rapidly quenching specimens, which had been annealed at a predetermined temperature, into ice water. TEM results reveal that (i) at 170 °C Vector 4111 has hexagonally-packed cylindrical microdomains of PS, (ii) at 185 °C the cylindrical and spherical microdomains of PS coexist, and (iii) as the temperature is increased further to 220 °C, only spherical microdomains of PS persist; i.e., the order−disorder transition temperature (T ODT) of Vector 4111 is higher than 220 °C. We found from the present study that the dynamic temperature sweep experiment under isochronal conditions failed to accurately determine the T ODT of Vector 4111 having a low volume fraction of PS blocks, while log G‘ vs log G‘‘ plots were very effective to investigate both OOT and ODT in Vector 4111.

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We have investigated the ordering dynamics of a triblock copolymer of a polystyrene-block-polyisoprene-block-polystyrene with asymmetric composition from the disordered sphere phase, where spherical microdomains exist but they have only a short-range liquidlike order, to the cylindrical and spherical microdomains with a long-range order. The ordering process was explored in situ by time-resolved small-angle X-ray scattering (SAXS), and the microdomain structures during the ordering process were observed by transmission electron microscopy (TEM) on specimens frozen at particular times in the ordering process. The SAXS observations show that there is an incubation period before the formation of the cylindrical and spherical microdomains with a long-range order. The coexistence of the ordered grains and the disordered spheres was observed in the TEM pictures taken during the ordering of both cylinders and spheres. The coexistence of the ordered grains and disordered spheres together with the existence of the incubation period suggests that this ordering proceeds via a nucleation and growth process. Moreover, it is revealed that the shape of the ordered grains in the matrix of the disordered spheres highly depends on the microdomain structures.

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We investigated the order−order and order−disorder transitions in a solution consisting of polystyrene-block-polyisoprene-block-polystyrene copolymer (Vector 4111 having weight-average molecular weights of 26 × 103 and 117 × 103 for polystyrene and polyisoprene block chains, respectively) and dioctyl phthalate (DOP), using small-angle X-ray scattering (SAXS), rheology, and transmission electron microscopy (TEM). SAXS results obtained in a heating process show (a) that, in the 85.5/14.5 weight fraction Vector 4111/DOP solution, (1) an order−order transition (OOT) takes place at 130−140 °C, (2) a lattice-disordering transition (LDT) takes place at 150−155 °C, and (3) an order−disorder transition (ODT) takes place at ca. 205 °C and (b) that, in the 73.2/26.8 Vector 4111/DOP solution, (1) an OOT takes place at 80−90 °C, (2) no LDT takes place because the structure formed after the OOT contains a considerable amount of lattice distortion, and (3) an ODT takes place at ca. 130 °C. Both SAXS and TEM results show that, in the 85.5/14.5 Vector 4111/DOP solution, hexagonally-packed cylindrical microdomains of polystyrene transform into spherical microdomains at the OOT temperature (T OOT). Comparison of SAXS results with rheological results indicates that the addition of 14.5 wt % DOP lowered both the T ODT and the lattice-disordering transition temperature of bulk Vector 4111 by ca. 50 °C. By assuming that DOP strictly plays the role of diluent, we estimated the ODT temperature (T ODT) of bulk Vector 4111 to be ca. 280 °C, which supports the conclusion drawn in our previous study that the T ODT of bulk Vector 4111 is much higher than 220 °C.

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We have investigated the morphology developed in the ordering process for a nearly symmetric polystyrene-block-polyisoprene diblock copolymer when the copolymer is rapidly brought from a disordered state to an ordered state. The ordering process was explored as a function of time and temperature primarily by transmission electron microscopy (TEM):  the microdomain structures formed during the ordering process were observed on specimens frozen at particular times in the ordering process. Complementary small-angle X-ray scattering experiments on the specimens before and after freezing assured that the structures existed before freezing were really conserved in the frozen specimens. The TEM observations showed that the ordered grains of the lamellar microdomain were developed in the matrix of the disordered phase and that the grains grew at the expense of the disordered phase at all the temperatures covered in this study. The coexistence of the ordered and disordered phases suggests that this ordering is a nucleation and growth process. We found that the shape of the lamellar grains developed in the disordered phase were very anisotropic at all stages and temperatures covered in this study:  the size along the lamellar normals was much larger than that parallel to the lamellar interfaces. Furthermore in the early stage of the ordering, the lamellae formed in the ordered grains were perforated but they eventually become solid lamellae.