Characteristics of Lamellar Mesophases in Strongly Segregated Broad Dispersity ABA Triblock Copolymers

We report the synthesis and characterization of a series of 13 strongly segregated poly­(lactide-<i>b</i>-1,4-butadiene-<i>b</i>-lactide) (LBL) triblock copolymers, in which a broad dispersity center B segment (<i><i><i>Đ</i></i></i> = <i>M</i>_w/<i>M</i>_n ∼ 1.7–1.9) is embedded between two narrow dispersity L end blocks (<i><i><i>Đ</i></i></i> ≤ 1.20). Derived from chain transfer ring-opening metathesis polymerization (ROMP-CT) of 1,5,9-cyclododecatriene in the presence of 1,4-diacetoxy-2-butene, α,ω-dihydroxytelechelic poly­(1,4-butadienes) serve as ring-opening transesterification polymerization (ROTEP) macroinitiators for the parallel synthesis of LBL triblock copolymers with <i>M</i>_n = 12.4–28.7 kg/mol and volume fractions <i>f</i>_B = 0.44–0.79. By determining the Flory–Huggins interaction parameter χ_LB = 0.192 at 155 °C from mean-field theory analyses of synchrotron X-ray scattering profiles for a narrow dispersity LB diblock copolymer, we estimate that the segregation strengths associated with the broad dispersity LBL copolymers range χ_LB<i>N</i> = 35.1–83.6. As compared to their narrow dispersity analogues reported herein, broad B segment dispersity shifts the composition-dependent lamellar phase window in LBL triblocks to higher values of <i>f</i>_B = 0.52–0.75. Contrary to previous reports of substantial dispersity-induced, lamellar domain spacing dilation in weakly segregated AB diblock and ABA triblock copolymers, strongly segregated LBL copolymers exhibit surprisingly similar domain sizes and scaling relations (<i>d</i> ∝ <i>N</i>^0.72±0.06) to their narrow dispersity analogues. This finding suggests that the magnitude of χ_AB determines the moment of the molar mass distribution that controls the observed lamellar domain spacing

Unexpected Consequences of Block Polydispersity on the Self-Assembly of ABA Triblock Copolymers

Controlled/“living” polymerizations and tandem polymerization methodologies offer enticing opportunities to enchain a wide variety of monomers into new, functional block copolymer materials with unusual physical properties. However, the use of these synthetic methods often introduces nontrivial molecular weight polydispersities, a type of chain length heterogeneity, into one or more of the copolymer blocks. While the self-assembly behavior of monodisperse AB diblock and ABA triblock copolymers is both experimentally and theoretically well understood, the effects of broadening the copolymer molecular weight distribution on block copolymer phase behavior are less well-explored. We report the melt-phase self-assembly behavior of SBS triblock copolymers (S = poly­(styrene) and B = poly­(1,4-butadiene)) comprised of a broad polydispersity B block (<i>M</i>_w/<i>M</i>_n = 1.73–2.00) flanked by relatively narrow dispersity S blocks (<i>M</i>_w/<i>M</i>_n = 1.09–1.36), in order to identify the effects of chain length heterogeneity on block copolymer self-assembly. Based on synchrotron small-angle X-ray scattering and transmission electron microscopy analyses of seventeen SBS triblock copolymers with poly­(1,4-butadiene) volume fractions 0.27 ≤ <i>f</i>_B ≤ 0.82, we demonstrate that polydisperse SBS triblock copolymers self-assemble into periodic structures with unexpectedly enhanced stabilities that greatly exceed those of equivalent monodisperse copolymers. The unprecedented stabilities of these polydisperse microphase separated melts are discussed in the context of a complete morphology diagram for this system, which demonstrates that narrow dispersity copolymers are not required for periodic nanoscale assembly

Mechanistic Study of Water Droplet Coalescence and Flocculation in Diluted Bitumen Emulsions with Additives Using Microfluidics

Synthetic crude oils derived from mined oil sands processed via the Clark hot water extraction process do not meet current specifications for pipeline transport and are corrosive to upgrader equipment by virtue of the high residual water content (2–5%) and salts. Formulated chemical additives used in this process can improve the oil quality by accelerating and enhancing the separation of water from oil. The identification and selection of these formulated additives is typically based on performance data collected in field testing for each component or blend. Herein, two methods are reported to study the effect of chemical additives on the phase separation behavior of water in diluted bitumen emulsions prepared in microfluidic devices. First, water droplets in diluted bitumen were created in the presence of chemical additives and the kinetics of droplet coalescence were compared for various additives and concentrations. Second, using a custom-made device geometry, water droplets in diluted bitumen were formed and aged prior to the addition of chemical additives. The treated droplets were observed to calculate the kinetics of droplet coalescence. The frequency of coalescence events was the same order of magnitude in both studies. The effectiveness of various additives can be determined by measuring the coalescence time, which is dominated by film drainage in the case of the best chemical additives

A Robust Oil-in-Oil Emulsion for the Nonaqueous Encapsulation of Hydrophilic Payloads

Compartmentalized structures widely exist in cellular systems (organelles) and perform essential functions in smart composite materials (microcapsules, vasculatures, and micelles) to provide localized functionality and enhance materials’ compatibility. An entirely water-free compartmentalization system is of significant value to the materials community as nonaqueous conditions are critical to packaging microcapsules with water-free hydrophilic payloads while avoiding energy-intensive drying steps. Few nonaqueous encapsulation techniques are known, especially when considering just the scalable processes that operate in batch mode. Herein, we report a robust oil-in-oil Pickering emulsion system that is compatible with nonaqueous interfacial reactions as required for encapsulation of hydrophilic payloads. A major conceptual advance of this work is the notion of the partitioning inhibitora chemical agent that greatly reduces the payload’s distribution between the emulsion’s two phases, thus providing appropriate conditions for emulsion-templated interfacial polymerization. As a specific example, an immiscible hydrocarbon–amine pair of liquids is emulsified by the incorporation of guanidinium chloride (GuHCl) as a partitioning inhibitor into the dispersed phase. Polyisobutylene (PIB) is added into the continuous phase as a viscosity modifier for suitable modification of interfacial polymerization kinetics. The combination of GuHCl and PIB is necessary to yield a robust emulsion with stable morphology for 3 weeks. Shell wall formation was accomplished by interfacial polymerization of isocyanates delivered through the continuous phase and polyamines from the droplet core. Diethylenetriamine (DETA)-loaded microcapsules were isolated in good yield, exhibiting high thermal and chemical stabilities with extended shelf-lives even when dispersed into a reactive epoxy resin. The polyamine phase is compatible with a variety of basic and hydrophilic actives, suggesting that this encapsulation technology is applicable to other hydrophilic payloads such as polyols, aromatic amines, and aromatic heterocyclic bases. Such payloads are important for the development of extended pot or shelf life systems and responsive coatings that report, protect, modify, and heal themselves without intervention

Bulk and Thin Film Morphological Behavior of Broad Dispersity Poly(styrene-<i>b-</i>methyl methacrylate) Diblock Copolymers

We describe the morphological implications of broad molecular weight dispersity on the bulk and thin film self-assembly behavior of seven model poly­(styrene-<i>block</i>-methyl methacrylate) (SM) diblock copolymers. Derived from sequential nitroxide-mediated polymerizations, these unimodal diblock copolymers are comprised of narrow dispersity S blocks (<i>Đ</i> ≤ 1.14) and broad dispersity M blocks (<i>Đ</i> ∼ 1.7) with total molecular weights <i>M</i>_n,total = 29.2–42.9 kg/mol and M volume fractions <i>f</i>_M = 0.35–0.63. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses demonstrate that these diblock copolymers microphase separate into lamellar and cylindrical morphologies with substantially larger microdomain spacings at lower overall molecular weights as compared to their narrow dispersity analogues. The observed microphase-separated melt stabilization is also accompanied by a substantial shift in the lamellar phase composition window to higher values of <i>f</i>_M. In thin films, these polydisperse copolymers form perpendicularly oriented morphologies with modest degrees of lateral order on substrates functionalized with P­(S-<i>ran</i>-MMA) neutral polymer brush layers

Phase Behavior of Poly(4-hydroxystyrene-<i>block</i>-styrene) Synthesized by Living Anionic Polymerization of an Acetal Protected Monomer

We have synthesized a series of poly­(4-(2-tetrahydropyranyloxy)­styrene) [P­(OTHPSt)] homopolymers by living anionic polymerization of the protected monomer (OTHPSt) in tetrahydrofuran at −78 °C, with excellent control over molecular weight and dispersity. The high <i>T</i>_g of P­(OTHPSt) led to facile purification and isolation of the polymer as a powder. Characterization of the POTHPSt homopolymer by nuclear Overhauser effect spectroscopy confirms the strong preference for the axial position of the relatively sterically demanding alkoxy phenyl group. By sequential monomer addition, a series of low to high molecular weight P­(OTHPSt-<i>b</i>-styrene) BCPs with narrow dispersities were synthesized. Quantitative deprotection of the THP groups yielded poly­(4-hydroxystyrene-<i>b</i>-styrene) with tunable molecular weights and compositions. The solid-state and melt-phase self-assembly of these diblocks was investigated using synchrotron small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Mean-field theory analysis of the temperature-dependent correlation-hole scattering for a disordered diblock was used to determine the interaction parameter as χ_HS/S(<i>T</i>) = (4.39 ± 0.83)/<i>T</i> + (0.109 ± 0.002), which is approximately 4 times larger than that of poly­(styrene-<i>b</i>-methyl methacrylate) with the same disproportionately high contribution of entropy to the free energy of mixing