Order−Disorder Transition Temperature Depression of a Diblock Copolymer Induced by the Addition of a Random Copolymer

Abstract

The change in the order−disorder transition temperature (T ODT) of a diblock copolymer, induced by the addition of a random copolymer, was investigated with synchrotron small-angle X-ray scattering and differential scanning calorimetry techniques. The studied block copolymer was poly(styrene-b-butadiene) containing 52 wt % styrene, and the added random copolymer was a small amount of poly(styrene-r-butadiene) containing 50 wt % styrene. The observed transition from the isotropic melt to the lamellar ordered structure appeared as a pronounced discontinuity in the peak's height and shape, and the estimated T ODT was found to decrease as the fraction of a random copolymer increased within the solubility limit (about 15 wt %). It was noted that the interdomain distance (D) decreased slightly upon the addition of a random copolymer, suggesting that the added random copolymer may have dissolved into the interfacial region of the microdomain. The plot of the reciprocal scattering maximum S-1(q*) as a function of the reciprocal absolute temperature T -1 can be fitted satisfactorily to the theoretical prediction based on the work of Fredrickson and Helfand. Also, the shift of T ODT in the blend is calculated with the theoretical prediction developed by Whitmore and Noolandi. The spinodal temperature (T S) and the T ODT decreased along a similar slope with the addition of a random copolymer.

Effect of composition of added random copolymer on the phase behavior of block copolymer

“…Styrene-butadiene diblock copolymer (denoted by S-B50) is the same material used in the previous study [19,20], which contains 52 wt% of styrene as determined by the NMR technique, and its M n and M w are 25,000 and 26,000, respectively. The blend samples were prepared by first dissolving a predetermined amount of each copolymer in toluene in the presence of an antioxidant (Irganox 1010, Ciba-Geigy Group) and then by slow evaporation of the solvent at room temperature.…”

“…8, the transition temperatures obtained with the SAXS, LS, and DSC experiments are plotted as a function of the weight fraction of SBR50 and SBR60 [19,20]. The 'L' phase above the transition line indicates the homogeneous mixed phase of S-B50 and SBR in a disordered state.…”

“…It was also found that the fraction of ABR solubilized into the A-B was very limited due to endothermic mixing between ABR and each block of A-B. An experimental study [19,20] on A-B/ABR blends was subsequently carried out, where the composition and molecular weight of ABR were similar to those of A-B. We showed that the T ODT and the interdomain distance (D) almost linearly decreased as the ABR fraction increased within the solubility limit.…”

“…[5]. There have also been some studies [16][17][18][19][20] on block copolymer/ block copolymer blends, or block copolymer/random copolymer blends, which are expected to exhibit different phase behavior from diblock copolymer/homopolymer blends.…”

Temperature-dependent location of a weakly segregated block copolymer in binary blends of block copolymers

“…Moreover, the thermal expansion effects, which could enlarge the domain spacing, would arise due to the delocalization of SB25 at higher temperatures while increasing temperature reduces the chain stretching. Considering that the thermal expansion effects were insufficient to overcome the effect of chain relaxation with increasing temperature in PS‐PBd or PS‐PI blends, it was deduced that the unusual domain spacing behavior was mainly caused by the effect of location of the dissolved SB25. Figure shows a schematic illustration of the domain spacing changes.…”