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Soft, conformally shaped thermoplastic elastomer (TPE) hydrogels producible from a moldable precursor material are desirable in many biomedical, surgical, and pharmaceutical applications. An innovative class of hydrogel networks was developed by employing photocurable, moldable solutions of melt-assembled spherical micelles formed from ω-anthracenylpolystyrene-b-poly(ethylene oxide) diblock copolymer. Photoinduced [4 + 4] cycloaddition (λ = 365 nm) of terminal anthracene groups populating the hydrophilic corona of each micelle was used to produce polystyrene-b-poly(ethylene oxide)-b-polystyrene triblock copolymer tethers or network strands among adjacent micelles. Structural uniformity in the micelle population was confirmed by small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM), and dynamic light scattering (DLS). Homogeneous dispersal of the assembled micelle building blocks in water resulted in spreadable or moldable photoactive micelle solutions, studied for their stability in solution and ability to rapidly form elastomeric hydrogels once irradiated. Once in molds, these solutions of varied concentration were irradiated to form soft TPE hydrogels with dynamic shear modulus controllable with irradiation time (triblock copolymer content), exhibiting prescribed shape consistent with high-fidelity conformal fill.

A series of thermally processable, phase-separating diblock copolymers made via sequential ATRP of styrene and styrenic ionic liquid (IL) monomers with various alkyl imidazolium substituents were synthesized to cover a wide range of volume fractions, most notably those on the IL-rich side of the phase diagram. Small-angle X-ray scattering (SAXS) analysis was used to confirm melt-state (and glassy state) phase behavior in which all four classic equilibrium diblock copolymer morphologies – body-centered cubic spheres (SBCC), hexagonally packed cylinders (Hex), lamellae (Lam), and notably, bicontinuous gyroid (Gyr) – were observed. These PS-PIL diblock copolymers were found to have a high degree of conformational asymmetry and/or electrostatic cohesion within the PIL block, highlighted by the shift of the Lam phase window with boundaries falling between fPIL = 0.31 and 0.55. Variation of the alkyl group appeared to influence the strength of the Flory-like interaction parameter of the system, χPS/PIL, such that simple substitution of methyl by n-butyl on the imidazolium IL substituent resulted in the emergence of the (notoriously segregation-sensitive) Gyr phase, superseding the persistent coexistence of Lam and Hex in the methyl-substituted imidazolium diblock copolymer phase diagram.

A simple method for spatially directed mechanical reinforcement and surface feature introduction on a photoactive block copolymer-based thermoplastic elastomer hydrogel is presented. The hydrogel material comprises two primary spherical micelle-forming block copolymer species: photoactive ω-anthracenylpolystyrene-b-poly(ethylene oxide) diblock copolymer (SO-anth) and polystyrene-b-poly(ethylene oxide)-b-polystyrene triblock copolymer (SOS). The PEO midblock of the SOS triblock copolymer species provides a physical tether between adjacent micelles, increasing mechanical robustness (modulus) with addition of bridging SOS chains. The photoactive SO-anth diblock copolymer contains a terminal anthracene unit capable of dimerization by application of 365 nm light to induce a [4 + 4] photocycloaddition. The ability to photocouple chain termini populating the outer shell of the hydrophilic micelle coronas produces additional SOS triblock copolymer in situ. While the initial population of SOS tethers act to form a...

Solvent-free, melt-state self-assembly of sphere-forming polystyrene-b-poly(ethylene oxide) diblock copolymer/polystyrene-b-poly(ethylene oxide)-b-polystyrene triblock copolymer (SO/SOS) blends was used to produce free-standing, room-temperature ionic liquid (RTIL) composite membranes with excellent mechanical properties and CO2/N2 separation performance. Membranes were prepared from vitrified SO/SOS diblock/triblock melts by swelling to greater than 94 wt% 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) ionic liquid. These free-standing composite membranes were evaluated for their CO2/N2 separation performance over a range of transmembrane pressures (26-413 kPa), with results traversing the 2008 Robeson upper bound. Even with such high loadings of neat [EMIM][TFSI], these membranes exhibit the mechanical properties of solid elastomers, evident by the ultimate tensile strength of 250 kPa and the compressive modulus at 40% strain of 348 kPa for the membranes with 46% triblock copolymer content (SOS46). Cyclic loading and unloading in both tension and compression revealed reversible elasticity, with no mechanical property degradation or permanent hysteresis detected. For each composition studied, membrane failure occurred at uniaxial extension ratios of 3.8. The CO2 permeability performance of these membranes was stable for 28 days of testing with no detectable RTIL leakage. Transmembrane pressures exceeding 400 kPa could be accommodated, with cyclic application of transmembrane pressure differentials at 230 kPa producing neither plastic deformation nor diminished performance in gas separations. Such behavior is intimately tied to the highly distensible and elastic nature of the melt-assembled diblock/triblock network underpinning this RTIL-based composite membrane design.

This report introduces a unique method of significantly improving toughness in highly swollen block copolymer-based thermoplastic elastomer (TPE) hydrogels by converting an intrinsically large population of dangling chain ends into a mechanically active second network. In one form, the TPE hydrogels developed by our group are based on swelling of a vitrified melt-blend of two amphiphilic block copolymer species, sphere-forming polystyrene-poly(ethylene oxide) (SO-H) diblock and triblock (SOS) copolymers. Here, the PEO midblock in the SOS triblock copolymer serves to tether adjacent PS spherical aggregates, producing hydrogel networks that are incredibly elastic and mechanically robust, preserving their shape even at the very high intrinsic swelling ratios produced at low SOS concentrations (e.g, 37 g of H2O/(g of polymer) at 3.3 mol % SOS). In this report, we advance the utility of this framework by exploiting the hundreds of dangling PEO chain ends per spherical aggregate to form a second, mechanically a...

Using a unique one-pot convergent anionic polymerization strategy, 18 (polystyrene)star-b-(polyisoprene)linear-b-(polystyrene)star (SnISn) pom-pom triblock copolymers were synthesized varying a range of architectural parameters including PS arm molecular weight (Mn,star), the number of arms contained in the star (n), and the PI midblock molecular weight (Mn,PI). A selected series of five of these 18, in which Mn,star was held approximately constant between 14.3 and 16.5 kDa, but with the numbers of arms in the star and PI midblock molecular weight varied, were selected for detailed characterization using rheology, AFM, and SAXS. The five selected all shared PS as the minority component, with star volume fractions (fPS) varying between 0.11 and 0.22. All samples showed clear phase separation, with three of the five adopting a highly ordered hexagonal packing of cylinders (HPC) confirmed through SAXS and AFM. The remaining two systems were limited to liquid-like packing of cylindrical domains (LLP). Longer ...

Tethered micelle hydrogel networks based on the solution assembly of amphiphilic ABA-type block copolymers are prevalent throughout the hydrogel literature. However, the mechanical response of such systems is often determined largely by the integrity of the micellar core produced during solution assembly, not by the elements of the network structure upon which it is based. Using a solvent-free fabrication method based on the melt-state self-assembly of sphere-forming polystyrene-b-poly(ethylene oxide) (SO) diblock and SOS triblock copolymers blends, we have been able to produce tethered micelle hydrogel networks with fully vitrified cores that enable the elements of the network structure to determine the mechanical response. Here, we explore the impact of using PEO midblocks of different lengths within the SOS tethers, in an effort to elucidate the role played by water content, tether concentration, and tether length in mechanical property determination. In doing so, we were able to establish coronal layer overlap as the primary contributing factor in regulating the dynamic elastic moduli exhibited by tethered micelle systems. Variation of either tether concentration or tether length could be used to tune the degree of coronal layer overlap, enabling direct and accurate control over hydrogel mechanical response. While such control is likely a unique feature of the melt-state fabrication approach applied here, the conclusions with respect to the role of coronal layer overlap and tether (bridging) concentration in determining the mechanical potential of the network should be applicable to all ABA-type tethered micelle systems, regardless of fabrication methodology.

Two poly(3-hexylthiophene) (P3HT) macromers containing a donor polymer with a polymerizable methacrylate (MA) end group, P3HT-CH2-MA and P3HT-(CH2)2-MA, have been synthesized, and P3HT-(CH2)2-MA has been successfully homopolymerized and copolymerized with methyl methacrylate (MMA) into stereoregular brush polymers and graft copolymers, respectively, using chiral ansa-zirconocene catalysts. Macromer P3HT-CH2-MA is too sterically hindered to polymerize by the current Zr catalysts, but macromer P3HT-(CH2)2-MA is readily polymerizable via either homopolymerization or copolymerization with MMA in a stereospecific fashion with both C2-ligated zirconocenium catalyst 1 and Cs-ligated zirconocenium catalyst 2. Thus, highly isotactic (with mm% ≥ 92%) and syndiotactic (with rr% ≥ 93%) brush polymers, it-PMA-g-P3HT and st-PMA-g-P3HT, as well as well-defined stereoregular graft copolymers with different grafted P3HT densities, it-P(M)MA-g-P3HT and st-P(M)MA-g-P3HT, have been synthesized using this controlled coordination-addition polymerization system under ambient conditions. These stereoregular brush polymers and graft copolymers exhibit both thermal (glass and melting) transitions with Tg and Tm values corresponding to transitions within the stereoregular P(M)MA and crystalline P3HT domains. Acceptor molecules such as C60 can be effectively encapsulated inside the helical cavity of st-P(M)MA-g-P3HT to form a unique supramolecular helical crystalline complex, thus offering a novel strategy to control the donor/acceptor solar cell domain morphology.

A series of imidazolium-based noncharged-charged diblock copolymers (1) was synthesized by the direct, sequential ATRP of styrene and styrenic imidazolium bis(trifluoromethyl)sulfonamide monomers with methyl, n-butyl, and n-decyl side-chains. Small-angle X-ray scattering studies on initial examples of 1 with a total of 50 repeat units and styrene:imidazolium-styrene repeat unit ratios of 25:25, 20:30, and 15:35 showed that their ability to form ordered nanostructures (i.e., sphere and cylinder phases) in their neat states depends on both the block ratio and the length of the alkyl side-chain on the imidazolium monomer. To our knowledge, the synthesis of imidazolium-based BCPs that form ordered, phase-separated nanostructures via direct ATRP of immiscible co-monomers is unprecedented. (C) 2014 Elsevier Ltd. All rights reserved.

The development of nanostructured polymeric systems containing directionally continuous poly(ionic liquid) (poly(IL)) domains has considerable implications toward a range of transport-dependent, energy-based technology applications. The controlled, synthetic integration of poly(IL)s into block copolymer (BCP) architectures provides a promising means to this end, based on their inherent ability to self-assemble into a range of defined, periodic morphologies. In this work, we report the melt-state phase behavior of an imidazolium-containing alkyl–ionic BCP system, derived from the sequential ring-opening metathesis polymerization (ROMP) of imidazolium- and alkyl-substituted norbornene monomer derivatives. A series of 16 BCP samples were synthesized, varying both the relative volume fraction of the poly(norbornene dodecyl ester) block (fDOD = 0.42–0.96) and the overall molecular weights of the block copolymers (Mn values from 5000–20 100 g mol–1). Through a combination of small-angle X-ray scattering (SAXS) ...

Direct access to nanostructured hydrogel networks through high fidelity photocuring of sphere-forming block copolymer melts is demonstrated. Hydrophobic junction points within the hydrogel network are based on an underlying lattice of body-centered cubic spheres (SBCC), produced via melt-state self-assembly of blended AB diblock and ABA triblock copolymer amphiphiles. Integrated thermally stable photocuring chemistry allows for in situ trapping of these spherical domains, independent from the required melt processing necessary to achieve the highly ordered BCC lattice. Swelling of the photocured solids in aqueous (and organic) media afforded highly elastic gels exhibiting excellent mechanical properties (G′ ∼ 103 Pa) and complete preservation of the cured solid shape. The hydrogels fabricated in this study were produced from partially epoxidized (19.6%, relative to diene repeat units) blends of polybutadiene-b-poly(ethylene oxide) diblock (PB–PEO, fPB = 0.13, Mn = 29 500 g mol–1, 88.5 mol %) and PB–PEO–PB...

In this work, we report the novel application of thermally stable photocuring chemistry toward high fidelity translation of block copolymer based melt-state morphologies into their equivalent solid analogues. The thermal stability of the cationic photcuring chemistry allows for both extended thermal processing prior to cure, as well as precise trapping of selected morphologies afforded by the temperature independent initiation mechanism. We demonstrate this powerful approach using a model polyisoprene-b-poly(ethylene oxide) (PI−PEO, fPEO = 0.39, Mn = 10 120 g mol−1) block copolymer, prepared by two step anionic polymerization and subsequent partial epoxidation (7.3−16.8 mol % relative to diene repeat units) with 3-chloroperoxybenzoic acid. Small angle X-ray scattering (SAXS) and dynamic rheology were used to determine morphological behavior of the block copolymers synthesized. The targeted PI−PEO parent block copolymer exhibited multiple melt-state morphologies including crystalline lamellae (Lc), hexagon...

Nanoporous materials with inherently tunable surface chemistries are poised to have a considerable impact in catalysis, separations, and nanopatterning. Using core−shell cylinder forming polystyrene-b-polyisoprene-b-polylactide (PS−PI−PLA) triblock terpolymers as templates, we were able to prepare aligned PI-coated nanoporous PS monoliths via the degradative removal of the cylindrical PLA cores. PS−PI−PLA precursors were synthesized using a combination of anionic (PS, PI) and ring-opening (PLA) polymerizations. The degree of order, alignment, and PLA degradation achievable was a strong function of molecular weight at a given triblock terpolymer composition. For intermediate molecular weight samples (25−28 kg mol-1), greater than 95% of the PLA was hydrolyzed through exposure of the monolith to a 0.1 wt % sodium dodecyl sulfate (SDS) solution in 0.5 N NaOH. However, low (17.5 kg mol-1) and high (46.8 kg mol-1) molecular weight samples of identical composition showed considerable resistance to PLA degradati...

The equilibrium phase behavior of 43 linear poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock copolymer melts, with molecular weights that place these materials near the order−disorder transition, is reported. Ordered phase morphologies were characterized using small-angle X-ray scattering, transmission electron microscopy, dynamic mechanical spectroscopy, and static birefringence measurements. Interpretation of these results was aided by a modeling technique that facilitates resolution of reciprocal and real-space experimental data, leading to definitive three-dimensional morphological structures. Three distinct multiply continuous network morphologies are identified across a range of compositions between 0.1 ≤ fO ≤ 0.3, situated between two-domain and three-domain lamellae, where fO represents the volume fraction of O blocks. Two cubic network phases, Q230 (core−shell double gyroid, Ia3d space group symmetry) and Q214 (alternating gyroid, I4132 space group symmetry), flank an orthorhombic networ...

We compare the phase behavior of a series of lithium perchlorate-doped poly(isoprene-b-styrene-b-ethylene oxide) (ISO) and poly(styrene-b-isoprene-b-ethylene oxide) (SIO) triblock copolymers. Complete phase diagram isopleths (fI = fS) are described for the lithium-doped ISO system and the previously reported lithium-doped SIO system. We examine the effects of block sequencing on the microstructures present in the doped SIO and ISO diagrams using small-angle X-ray scattering. Three phases were identified in the doped ISO phase diagram isopleth: two-domain lamellae (LAM2), core−shell cylinders (CSC), and three-domain lamellae (LAM3). The order−disorder transition temperatures increase dramatically upon doping and salt loadings up to [O]:[Li] concentrations of 3:1 are accomplished without macrophase separation. The increase in segregation strength in the ISO system upon doping leads to a disappearance of the more geometrically elaborate network phase in favor of the CSC phase as a result of the imbalance in...

We present characterization data for linear poly(isoprene-b-styrene-b-ethylene oxide) (PI−PS−PEO) triblock copolymers containing equal volume fractions of PI and PS (fPI = fPS) and varying amounts of PEO, 0 ≤ fPEO ≤ 1/3. Detailed characterization by TEM, SAXS, dynamic mechanical spectroscopy, static birefringence, and DSC indicates three distinct morphologies: two-domain lamellae, a three-domain noncubic triply periodic network structure, and three-domain lamellae with increasing PEO content. This phase behavior is in striking contrast with the homologous PS−PI−PEO triblock phase diagram, reported earlier, which contains four different morphologies between the limiting two- and three-domain lamellae phases. Preliminary analysis suggests the noncubic network structure contains elementary units of 3-fold coordination, yet fundamentally distinct from the cubic core−shell gyroid topology previously demonstrated in PS−PI−PEO. This tentatively assigned model is a structural hybrid of the gyroid and perforated ...

We report on the phase behavior of a system of lithium perchlorate-doped poly(styrene-b-isoprene-b-ethylene oxide) (SIO) triblock copolymers. Two complete phase diagrams are described along the isopleth formed by equal volume fractions of polystyrene and polyisoprene and varying poly(ethylene oxide) contents at ether oxygen-to-lithium ratios of 48:1 and 24:1 between 70 and 200 °C. Our results, based primarily on small-angle X-ray scattering (SAXS) data, reveal four phases as a function of PEO and salt content: two-domain lamellae (LAM2), a pillared lamellar structure (PLS), core−shell cylinders (CSC), and three-domain lamellae (LAM3). Two microstructures present in the neat material, core−shell gyroid (CSG), and semiperforated lamellae (SPL), are replaced by the CSC phase in the doped systems. In addition, the order−disorder transition temperatures at low PEO content increase dramatically with the addition of salt. Within the CSC phase, LiClO4 can be dispersed up to a loading of 3:1 without inducing macr...

We report on the characterization of the morphological behavior expressed between the symmetric AB diblock and ABC triblock copolymer states. Experimentally, a gradual transformation between these states was achieved through systematic addition of PEO to a single symmetric PS−PI diblock copolymer (MW ∼ 18 800 g/mol), resulting in a series of 10 poly(styrene-b-isoprene-b-ethylene oxide) triblock copolymers varying only in the amount of PEO added. Final compositions ranged from 2.9 to 33.2 vol % (experimentally symmetric) PEO, with the remaining volume necessarily divided equally between the PS and PI segments. The molecular weight of the parent diblock was chosen such that resulting triblocks would undergo order−disorder transitions (ODTs) at experimentally accessible temperatures over much of the composition range studied. Our results focus on the detection and characterization of six morphologies observed to form between these two symmetric states and some of the kinetic and directional (heating vs cooli...

We describe the preparation of polystyrene−polyisoprene−polylactide and polyisoprene−polystyrene−polylactide ABC triblock terpolymer thin films followed by removal of one or both sacrificial components (i.e., polylactide and polyisoprene) to give large area arrays of nanopores and more complex “nanobushing” structures, respectively.

Asymmetric polystyrene-polylactide (PS-PLA) bottlebrush block copolymers have been shown to self-assemble into a cylindrical morphology with large domain spacings. PLA cylinders can be selectively etched out of the shear-aligned polymer monoliths to generate nanoporous materials with an average cylindrical pore diameter of 55 nm. The remaining bottlebrush backbone provides a functional, hydrophilic coating inside the nanopores. This methodology significantly expands the range of pore sizes attainable in block copolymer based nanoporous materials.

Ordered nanoporous plastics with hydrophilic pore surfaces were prepared by the degradative removal of polylactide from a self-organised, multi-component composite containing two block copolymers: polystyrene-polylactide and polystyrene-polyethylene oxide. The solid-state characterization of blends containing up to 12 wt.% polyethylene oxide was consistent with nanoscopic cylinders of mixed polyethylene oxide and polylactide hexagonally packed in a polystyrene matrix. Orientation of these materials through simple channel die processing resulted in good cylinder alignment. Subsequent methanolysis/hydrolysis of the polylactide component gave nanoporous polystyrene with polyethylene oxide coated pores. The resulting nanoporous materials were able to imbibe water, in contrast to nanoporous polystyrene with no polyethylene oxide component.

Novel ABC triblock copolymers containing hydrophobic, imidazolium ionic liquid (IL)-based ionic, and non-charged hydrophilic blocks were synthesized by direct sequential, ring-opening metathesis polymerization (ROMP) of three chemically immiscible norborene monomers. The resulting ABC triblock copolymers were found by small-angle X-ray scattering to phase-separate into different nanostructures in their pure melt states, depending on their block sequence and compositions. Supported composite membranes of these triblock copolymers were successfully fabricated with defect-free, ≤20 microns thick top coatings. Preliminary CO2/light gas transport studies demonstrated the potential of this new type of IL-based block copolymer material for gas separation applications.

A new structural motif for the generation of highly distensible, highly elastic, nanostructured hydrogels is presented. Based on the swelling of vitrified melt-phase blends of sphere-forming polystyrene–poly(ethylene oxide) diblock and polystyrene–poly(ethylene oxide)–polystyrene triblock copolymers, the equilibrium swelling ratio (3.8–36.9 g H2O per g polymer) and dynamic elastic modulus (G′ = 1700–160 000 Pa) of these novel hydrogel systems were found to be remarkably tunable through simple manipulation of temperature (10–50 °C) and triblock copolymer content (3.3–72.0 mol%). Mechanical properties were found to be almost exclusively a function of triblock copolymer content, independent of temperature induced changes in swelling ratio. The resulting hydrogels were highly elastic at all swelling ratios with G′/G″ ≈ 102 for the range of triblock copolymer concentrations examined. Hydrogel samples exhibited excellent preservation of dry polymer shape upon swelling, with complete recovery of both shape and mechanical performance following repeated compression–decompression cycles.