Comprehensive Phase Behavior of Poly(isoprene-b-styrene-b-ethylene oxide) Triblock Copolymers

Abstract

The phase behavior of 44 poly(isoprene-b-styrene-b-ethylene oxide) (ISO) linear triblock copolymer melts was investigated at weak to intermediate segregation strengths and spanning a comprehensive range of compositions. Phases were characterized by a combination of experimental techniques, including small-angle X-ray scattering, dynamic mechanical spectroscopy, transmission electron microscopy, and birefringence measurements. Combined with our previous results, six different stable ordered state symmetries have been identified: lamellae (LAM), Fddd orthorhombic network (O 70 ), double gyroid (Q 230 ), alternating gyroid (Q 214 ), hexagonal (HEX), and body-centered cubic (BCC). The phase map of ISO specimens was found to be somewhat asymmetric around the f I ) f O isopleth. This work provides a guide for theoretical studies and gives insight into the intricate effects of various parameters on the self-assembly of ABC triblock copolymers. Experimental SAXS data evaluated with a simple scattering intensity model show that local mixing varies continuously across the phase map between states of two-and three-domain segregation. IntroductionMore than four decades of research has established quantitative and predictive theoretical tools for anticipating the phase behavior of AB diblock copolymers, which complement a rich collection of experimental data. 1-7 Addition of a third chemically distinct C block to an AB diblock expands the phase complexity and the number of experimentally adjustable parameters, resulting in a fascinating, yet largely unpredictable, array of morphologies. Nearly three dozen ordered phases have been discovered in ABC triblocks 2,8-23 compared to just four well-established equilibrium phases in AB diblocks. This expanded scope is both stimulating and intimidating. Three different polymer blocks offers desirable features such as increased molecular design opportunities and increased functionality. However, additional blocks imply additional variables, with a geometrically expanding degree of complexity with each new element.Self-assembly of block copolymers in the bulk liquid state is governed by three sets of parameters: composition, interfacial tension, and sequencing. (The block statistical segment lengths constitute a fourth, less critical, set of variables.) For AB diblocks there is one composition variable, f A ) 1 -f B , one segment-segment interaction parameter, AB , and one sequence. Linear ABC triblocks are governed by two independent composition variables, three ij 's, and three distinct sequences. Choosing among these parameters in order to target a specific morphology for a particular application represents a daunting task, complicated by a lack of theoretical guidance and relatively few comprehensive experimental phase portraits.Different types of ABC triblock copolymers (specifically referring to those in linear architectures and in the bulk liquid state) have been investigated by a host of research groups, such as Hashimoto et al., 29,30 Matsushita et al.,15,16,31,32 Stadler et al...

Manipulating the ABCs of self-assembly via low-χ block polymer design

“…Both the relative and absolute magnitudes of each χ ij , convolved with the molecular sequence, underpin the self-assembly of multiblock polymers. For example, given I, S, and O blocks with χ IO > χ IS ≈ χ SO (47,48), SIO connectivity imposes costly high-χ interactions between adjacent blocks (χ BC > χ AB ≈ χ AC ), whereas ISO connectivity alleviates this penalty by not inherently requiring I/O (A/C) interfaces. ISO and SIO phase diagrams are consequently distinct due to so-called frustration.…”

Ordered Three- and Five-ply Nanocomposites from ABC Block Terpolymer Microphase Separation with Niobia and Aluminosilicate Sols

“…The equilibrium morphologies of ISO3 and ISO4 were previously determined to be 2-domain lamellar and O 70 , respectively 14. The O 70 is a tricontinuous orthorhombic network structure which was first identified in 2002 and has been detailed elsewhere 14, 18, 26, 28. ISO polymers are amphiphilic, having a hydrophilic O block and two hydrophobic blocks, I and S. The hydrophilic oxide sol particles are expected to selectively swell the O block.…”

Dynamic Assembly of Block-Copolymers

“…Playing with the flexibility/rigidity of the polymer segments, various new morphologies could be discovered and some of them have been confirmed experimentally [110][111][112]. A series of papers [113][114][115][116][117] In this case, the morphology seems to be governed by the relatively weak incompatibility of the end blocks PS and PMMA rather than the strong incompatibility of the polybutadiene (PB) or poly(ethylene-co-butylene).…”