Bicomponent Block Copolymers Derived from One or More Random Copolymers as an Alternative Route to Controllable Phase Behavior

Ashraf, Arman; Ryan, J. J.; Satkowski, Michael M.; Lee, Byeongdu; Smith, Steven D.; Spontak, Richard J.

doi:10.1002/marc.201700207

Cited by 18 publications

(22 citation statements)

References 55 publications

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“…This suggests that the relatively thick and diffuse interfaces (and any compositional gradients) of these low-χ diblocks resulted in a less drastic change in the viscoelastic properties at the T ODT and thus a broader transition from order to disorder. Similar observations have been reported for block random and tapered copolymers. − Regardless, the complementary results from DSC and DMA strongly suggest that the diblock polymers with XS ≥ 26 are comprised of well-structured microphase-segregated domains, as is expected for either a fluctuating disordered or an ordered morphology.…”

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confidence: 74%

Molecular Engineering of Nanostructures in Disordered Block Polymers

Hampu

2020

ACS Macro Lett.

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A series of symmetric poly(methyl methacrylate-stat-styrene)-block-polylactide (P(MMA-s-S)-b-PLA) diblock terpolymers with nearly constant molar masses yet varying block interaction parameters were synthesized as a model system to probe the extent and utility of composition fluctuations in the disordered state. A combination of differential scanning calorimetry, dynamic mechanical analysis, and small-angle X-ray scattering revealed that a broad range of segregation strengths ranging from what we ascribe to essentially a mean-field disordered to a fluctuating disordered to an ordered system could be readily obtained by tuning the molar fraction of styrene in these diblocks. The P(MMA-s-S)-b-PLA diblocks were annealed above their order–disorder transition temperatures (T ODT) and rapidly quenched to low temperatures to trap the disordered state via vitrification, as confirmed by scanning electron microscopy. Small-angle X-ray scattering and N2 sorption analysis post-removal of PLA demonstrated that a transition from a very weakly structured, mean-field-like melt to a bicontinuous fluctuating disordered state occurred with increasing segregation strength. This work demonstrates that the extent of microphase segregation as well as the domain continuity of the disordered block polymer melt can be tuned using both synthetic design and thermal stimuli, guiding the design of disordered block polymers with targeted nanostructures that have potential technological utility.

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confidence: 74%

Molecular Engineering of Nanostructures in Disordered Block Polymers

Hampu

2020

ACS Macro Lett.

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“…Overview of reported polymer architectures based on different PS and PI sequences. ,,,, F V,S is the instantaneous volume incorporation of styrene.…”

Section: Introductionmentioning

confidence: 99%

“…Here, the architectures were synthesized by two subsequent random copolymerizations with highly diverging monomer feeds ( f ) for each random block (Figure e). Hence, for these so-called “block random copolymers”, χ eff could be varied by the inherent composition contrast of both blocks . This versatile use of in situ generated, tailored monomer sequences ,,− emphasizes the importance of (co)polymerization kinetics to engineer monomer sequences and tailor material properties.…”

Section: Introductionmentioning

confidence: 99%

Tetrahydrofuran: More than a “Randomizer” in the Living Anionic Copolymerization of Styrene and Isoprene: Kinetics, Microstructures, Morphologies, and Mechanical Properties

et al. 2020

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The statistical anionic copolymerization of isoprene (I) and styrene (S) is commonly used to synthesize tapered block copolymers, enabling control of the phase behavior by adjusting the order–disorder transition temperature, T ODT. Alkyllithium initiation in hydrocarbons is known to afford tapered block copolymers of I and S in one step. The effect of tetrahydrofuran (THF) on the copolymerization kinetics and the resulting copolymers was systematically investigated by increasing the [THF]/[Li] ratio from 0 to 2500 (0 to 29%vol THF). For this purpose, in situ near-infrared (NIR) spectroscopy was employed as a versatile and fast method to track the highly accelerated consumption of the individual monomers. Changes in the I/S comonomer sequence and in the polyisoprene (PI) regioisomers, caused by variation of the THF concentration, were independently determined via NMR and in situ NIR spectroscopy. Reactivity ratios were determined as a function of the [THF]/[Li] ratio. They revealed a gradual reversal from r I ≫ r S over r I ≈ r S to r I ≪ r S. Corresponding changes in the copolymer composition profile up to a complete inversion are evident in thermal properties and morphologies. Although all copolymers possess the same comonomer composition (50%mol = 57%vol polystyrene (PS) units), small-angle X-ray scattering and transmission electron microscopy give evidence of a wide variation in bulk morphologies depending on the gradient profile. Overall, the phase diagram is symmetric, and the succession of phases bears certain similarities to the PI-b-PS case. This is discussed in terms of the increasing incompatibility of PS with 3,4-PI and the more symmetric polymer conformational parameter. The degree of segregation, as well as the nanodomain structure, was found to control the mechanical properties, showing a remarkably different viscoelastic response leading to either hard/brittle or ductile/soft materials. The accessibility of tailored gradient profiles, as well as their in-depth understanding by simply using THF as a microstructural modifier, opens a variety of possible applications. As an example, the synthesis of a PI-selective hydrogenated tapered triblock, possessing a THF-modified, phase-compatibilizing tapered block incorporated in the well-established SIS block architecture, is presented.

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“…Thermodynamic incompatibility drives BCs to order into an assortment of classical (e.g., spherical, cylindrical, or lamellar) or spatially complex (e.g., gyroid, helical, or Fddd ) morphologies. Judicious chemical design of BCs in terms of factors, such as chemical constitution and molecular composition, weight and architecture, as well as targeted blending with solvents or other macromolecules, yields customized phase behavior and properties, as well as morphologies with specific spatial characteristics. While some BC morphologies are intentionally defective for connectivity purposes, most efforts have endeavored to generate near‐equilibrium nanostructures that can compare directly with theory or establish definitive structure–property relationships .…”

Section: Methodsmentioning

confidence: 99%

Ordering and Grain Growth in Charged Block Copolymer Bulk Films: A Comparison of Solvent‐Related Processes

Ryan

Mineart

Lee

et al. 2018

Adv Materials Inter

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for ubiquitous nanotechnologies. [1][2][3][4] Thermodynamic incompatibility [5][6][7] drives BCs to order into an assortment of classical (e.g., spherical, cylindrical, or lamellar) or spatially complex (e.g., gyroid, [8] helical, [9] or Fddd [10,11] ) morphologies. Judicious chemical design of BCs in terms of factors, such as chemical constitution [12][13][14] and molecular composition, weight and architecture, [15] as well as targeted blending with solvents [16,17] or other macromolecules, [18,19] yields customized phase behavior and properties, as well as morphologies with specific spatial characteristics. While some BC morphologies are intentionally defective for connectivity purposes, [20,21] most efforts have endeavored to generate near-equilibrium nanostructures that can compare directly with theory [22,23] or establish definitive structure-property relationships. [24] More recently, directed self-assembly strategies that rely on BC crystallization, [25,26] chemical coordination, [26] or surface-induced alignment [27] have resulted in nearly monodisperse nanofibers grown in living fashion, designer superstructures with hierarchical features, or nanotemplates with precise spatial modulation, respectively. Another important aspect of morphological control includes orientation, which is crucial in the development of anisotropic mechanical properties, [28] defect-free diffusive pathways, [29] or wavelength-specific photonic guides. [30,31] Methods that promote morphological refinement and orientation in nonpolar BCs rely on thermal [32,33] and solvent [34,35] treatment.Block ionomers (BIs), charged block copolymers possessing at least one block with ionic moieties, combine the ability of BCs to microphase order [36,37] with the hydrophilic/ionophilic nature of polyelectrolytes and are therefore of interest in fuel cells [38] and water purification. [39,40] In addition, they have been utilized as electroactive media, [41] amphoteric gas-separation membranes, [42][43][44] and organic photovoltaics. [45] Unlike their BC analogs, BIs suffer from a significant complication-the formation of ionic clusters, which often trap nonequilibrium morphologies. To avoid degradation issues of BI bulk films induced by thermal annealing, we have previously reported that the nanostructural elements in BIs can be not only solvent templated [46] during film casting but also solvent annealed [47] to promote equilibration of dried films. Here, we consider three poly[While prior efforts have demonstrated that the morphologies of block copolymer (BC) bulk films can be controlled through judicious chemical design and thermal annealing, recent interest has focused on regulating the orientation of BC nanostructures and minimizing defects. Thermal processes developed to achieve this purpose for nonpolar BCs are not, however, suitable for orienting microphase-ordered BCs composed of at least one block with charged moieties that can form thermally stable ionic clusters. To overcome this challenge, we have previously applied solvent-vapor (...

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Bicomponent Block Copolymers Derived from One or More Random Copolymers as an Alternative Route to Controllable Phase Behavior

Cited by 18 publications

References 55 publications

Molecular Engineering of Nanostructures in Disordered Block Polymers

Molecular Engineering of Nanostructures in Disordered Block Polymers

Tetrahydrofuran: More than a “Randomizer” in the Living Anionic Copolymerization of Styrene and Isoprene: Kinetics, Microstructures, Morphologies, and Mechanical Properties

Ordering and Grain Growth in Charged Block Copolymer Bulk Films: A Comparison of Solvent‐Related Processes

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