Interchain Hydrogen Bonding\nInteraction Induced phase\nBehaviors of Poly(ethylene oxide)-<i>b</i>-poly(<i>N</i>-vinylcarbazole)/Poly(acrylic acid) Blend

Abstract

In this paper, we study an αβ/C blend system\ncomposed\nof a diblcok copolymer of poly­(ethylene oxide)₁₁₃-<i>b</i>-poly­(<i>N</i>-vinylcarbazole)₇₇ (PEO₁₁₃-<i>b</i>-PVK₇₇) and a homopolymer\nof poly­(acrylic acid) (PAA) with a weight-average molecular weight\nof 1900 g/mol. The phase behavior of the blend was characterized using\nvarious techniques including Fourier transform infrared spectroscopy,\ndifferential scanning calorimetry, small-angle X-ray scattering, and\ntransmission electron microscopy. The experimental results indicate\nthat while the PEO and PVK blocks are miscible in bulk state, adding\nPAA into the diblock can lead to microphase separation of the blend\ndue to the interchain hydrogen bonding complexation between PEO and\nPAA. The phase morphology of the blend is strongly dependent on the\nPAA composition. Only with sufficiently high weight fraction of PAA\n(<i>wt</i>_PAA), the blends can present ordered\nmicrophase-separated structures, although the long-range order is\nnot well developed. For 40% < <i>wt</i>_PAA < 70% (corresponding to the PVK volume fraction between 44% and\n22%), the ordered phase is changed from lamella to cylinder to cubic\nphase with increasing <i>wt</i>_PAA. Further increase\nof PAA content results in spheres with the core of PVK dispersed in\nthe matrix of PAA. The diameters of the PVK cores of cylinders and\nspheres are very close to the twice of the unperturbed end-to-end\ndistance of the PVK block, indicating that the rather rigid PVK block\nis hard to be deformed during microphase separation. The PAA composition\ndependence of the blend phase behavior illustrates that the degree\nof PEO/PAA complexation dominates the segregation strength. After\nthe microphase separation occurs, the phase morphology can be adjusted\nby varying the PAA content.