Showing papers by "Marc A. Hillmyer published in 2015"

Mechanically Activated, Catalyst-Free Polyhydroxyurethane Vitrimers

Abstract: Vitrimers are polymer networks whose cross-links undergo associative exchange processes at elevated temperature, usually in the presence of an embedded catalyst. This design feature enables the reshaping of materials with mechanical properties similar to thermoset resins. Here we report a new class of vitrimers consisting of polyhydroxyurethanes (PHUs) derived from six-membered cyclic carbonates and amines. PHU networks relax stress and may be reprocessed at elevated temperature and pressure in the absence of an external catalyst. The as-synthesized networks exhibit tensile properties comparable to those of leading thermosets and recover ca. 75% of their as-synthesized values following reprocessing. Stress relaxation occurs through an associative process involving nucleophilic addition of free hydroxyl groups to the carbamate linkages and exhibits an Arrhenius activation energy of 111 ± 10 kJ/mol, which is lower than that observed for molecular model compounds (148 ± 7 kJ/mol). These findings suggest that...

High χ–Low N Block Polymers: How Far Can We Go?

Abstract: Block polymers incorporating highly incompatible segments are termed “high χ” polymers, where χ is the Flory–Huggins interaction parameter. These materials have attracted a great deal of interest because low molar mass versions allow for the formation of microphase-separated domains with very small (<10 nm) feature sizes useful for nanopatterning at these extreme dimensions. Given that well-established photolithographic techniques now face difficult challenges of implementation at scales of 10 nm and below, the drive to further develop high χ block polymers is motivated by trends in the microelectronics industry. This Viewpoint highlights our perspective on this niche of block polymer self-assembly. We first briefly review the relevant recent literature, exploring the various block polymer compositions that have been specifically designed for small feature size patterning. We then overview the now standard method for the benchmarking χ values between different pairs of polymers and the consequences of low...

Hierarchically porous polymers from hyper-cross-linked block polymer precursors

Abstract: We report synthesis of hierarchically porous polymers (HPPs) consisting of micropores and well-defined 3D continuous mesopores by combination of hyper-cross-linking and block polymer self-assembly. Copolymerization of 4-vinylbenzyl chloride (VBzCl) with divinylbenzene (DVB) in the presence of polylactide (PLA) macro-chain-transfer agent produced a cross-linked block polymer precursor PLA-b-P(VBzCl-co-DVB) via reversible addition-fragmentation chain transfer polymerization. A nanoscopic bicontinuous morphology containing PLA and P(VBzCl-co-DVB) microdomains was obtained as a result of polymerization-induced microphase separation. While a basic treatment of the precursor selectively removed PLA to yield a reticulated mesoporous polymer, hyper-cross-linking of the precursor by FeCl3 generated micropores in the P(VBzCl-co-DVB) microdomain via Friedel-Crafts alkylation and simultaneously degraded PLA to produce the HPP containing micropores in the mesoporous framework. The mesopore size of the HPP could be precisely controlled from 6 to 15 nm by controlling the molar mass of PLA. We demonstrate acceleration in adsorption rate in the HPP compared to a hyper-cross-linked microporous polymer.

Bottlebrush Block Polymers: Quantitative Theory and Experiments.

Abstract: The self-assembly of bottlebrush block polymers into a lamellar phase was investigated using a combination of experiment and self-consistent field theory (SCFT). Nine diblock bottlebrush polymers were synthesized with atactic polypropylene side chains (block A) and polystyrene side chains (block B) attached to poly(norbornene) backbones of various contour lengths, L, and the resulting lamellar structures were analyzed using small-angle X-ray scattering. The scaling of the lamellar period, d0 ∼ Lγ, exhibited an increasing exponent from γ ≈ 0.3 at small L to γ ≈ 0.9 at large L. The small exponents occurred for starlike molecules where the size of the side chains is comparable to L, while the larger exponents occurred for the more brushlike molecules where the side chains extend radially outward from the backbone. The bottlebrushes were then modeled using flexible side chains of types A and B attached to a semiflexible backbone with an adjustable persistence length, ξb. The resulting SCFT predictions for d0 ...

Linear Rheology of Polyolefin-Based Bottlebrush Polymers

Abstract: Two series of polyolefin-based bottlebrush polymers were synthesized using ring-opening metathesis polymerization of norbornenyl-functionalized macromonomers to compare the rheology of systems with and without the presence of side chain entanglement. The first series of bottlebrushes includes atactic polypropylene (aPP) branches with a fixed length of Mbranch = 2.05 kg/mol and variable backbone degree of polymerization ranging from 11 to 732 (Mw = 22–1500 kg/mol). The branches in this series are shorter than the entanglement molecular weight of aPP (Mbranch/Me ≈ 0.5). The second series utilizes poly(ethylene-alt-propylene) (PEP) branches with Mbranch = 6.7 kg/mol and variable backbone degree of polymerization ranging from 13 to 627 (Mw = 89–4200 kg/mol). The branches in this series exceed the entanglement molecular weight of PEP (Mbranch/Me ≈ 3.5). The linear viscoelastic responses of each sample were examined using small-amplitude oscillatory shear measurements, and dynamic master curves were constructed...

Hierarchically Porous Polymer Monoliths by Combining Controlled Macro- and Microphase Separation.

Abstract: The ability to tune polymer monolith porosity on multiple length scales is desirable for applications in liquid separations, catalysis, and bioengineering. To this end, we have developed a facile synthetic route to nanoporous polymer monoliths based on controlled polymerization of styrene and divinylbenzene from a poly(lactide) macro-chain transfer agent in the presence of nonreactive poly(ethylene oxide) (PEO). Simple variations in the volume fraction and/or molar mass of PEO lead to either polymerization-induced microphase separation or simultaneous macro- and microphase separation. These processes dictate the resultant morphology and allow for control of the macro- and microstructure of the monoliths. Subsequent selective etching produces monoliths with morphologies that can be tailored from mesoporous, with control over mesopore size, to hierarchically meso- and macroporous, with percolating macropores. This convenient synthetic route to porous polymer monoliths has the potential to be useful in appli...

Reactive Compatibilization of Polylactide/Polypropylene Blends

Abstract: Polylactide (PLA) was melt blended with either polypropylene (PP) or a polypropylene based elastomer (PBE, Vistamaxx) in an effort to improve its mechanical properties. An ethylene–glycidyl methacrylate–methyl acrylate terpolymer (PEGMMA, Lotader) was utilized as compatibilizer through coupling to the end groups of PLA. Graft copolymers formed enhanced the adhesion between PLA and polyolefin phases and lowered the interfacial tension. The morphological, mechanical, and rheological properties of the PLA/polyolefin compatibilized blends were investigated, and the blends exhibited substantial improvement in elongation at break and tensile toughness as compared to the corresponding binary blends. The remarkable efficacy of PEGMMA as a reactive compatibilizing agent allows the bridging of two immiscible but important classes of thermoplastics, polylactide and polypropylene, and the production of ductile PLA/PP blend materials.

Evolution of morphology, modulus, and conductivity in polymer electrolytes prepared via polymerization-induced phase separation

Abstract: Polymer electrolytes are alternatives to liquid electrolytes traditionally used in electrochemical devices such as lithium-ion batteries and fuel cells. In particular, block polymer electrolytes are promising candidates because they self-assemble into well-defined microstructures, in which orthogonal properties can be integrated into a single material (e.g., high modulus in domain A, fast ion transport in domain B). However, the performance of block polymer electrolytes often falls short, due to the lack of long-range continuity of both domains and relatively low strength. We recently reported a simple, one-pot synthetic strategy to prepare polymer electrolytes with the highest reported combination of modulus and ionic conductivity, attributes enabled by a co-continuous, cross-linked network morphology. In this work we aim to understand the mechanism by which this nanoscale morphology is formed by performing a series of in situ, time-resolved experiments—small-angle X-ray scattering, conductivity, rheolog...

Detection of pharmaceutical drug crystallites in solid dispersions by transmission electron microscopy.

Abstract: We explored the use of transmission electron microscopy (TEM) to evaluate the crystallinity of griseofulvin (GF)/hydroxypropyl methylcellulose acetate succinate (HPMCAS) solid dispersions. TEM, which provides both real-space images and electron diffraction patterns, was used to unambiguously identify GF crystals in spray dried GF. Using TEM, we were also able to detect GF crystals in a physical mixture of spray dried GF particles and spray dried HPMCAS particles with an overall crystallinity of ∼3 vol %, below the practical lower limit of detection for laboratory-scale wide-angle X-ray scattering (WAXS). Using TEM and WAXS, we did not find crystals in GF/HPMCAS solid dispersions with GF loadings of 5, 10, and 50 wt %. However, we detected GF crystals in annealed 5 wt % GF solid dispersion using TEM, whereas we did not detect crystals using in situ WAXS and modulated differential scanning calorimetry, thereby establishing the superior crystal detection sensitivity of TEM. We also performed TEM analysis of ...

Functionalized regio-regular linear polyethylenes from the ROMP of 3-substituted cyclooctenes

Abstract: We demonstrated that the ring-opening metathesis polymerization (ROMP) of 3-substituted cyclooctenes bearing polar substituents allows the synthesis of highly regio- and stereo-regular polymers. A series of polyalkenamers with 90–99 % head-to-tail/trans configuration were synthetized in good yields (33–87 % yield). Upon saturation of the backbone using diimide, these polymers represent a class of linear polyethylene derivatives where the polar side chain is located on every eighth carbon. The thermal properties of both the saturated and unsaturated polymers depend strongly on the size and polarity of the functional side groups. The results presented here demonstrate that the 3-substituted cyclooctenes can be used not only for the synthesis of precisely functionalized polyethylene derivatives, but also to participate in the ring-opening metathesis copolymerization with unfunctionalized cyclic olefins to generate copolymers with tunable properties.

Poly(cyclohexylethylene)-block-poly(ethylene oxide) block polymers for metal oxide templating

Abstract: A series of poly(cyclohexylethylene)-block-poly(ethylene oxide) (CEO) diblock copolymers were synthesized through tandem anionic polymerizations and heterogeneous catalytic hydrogenation. Solvent-annealed CEO diblock films were used to template dense arrays of inorganic oxide nanodots via simple spin coating of an inorganic precursor solution atop the ordered film. The substantial chemical dissimilarity of the two blocks enables (i) selective inclusion of the inorganic precursor within the PEO domain and (ii) the formation of exceptionally small feature sizes due to a relatively large interaction parameter estimated from mean-field analysis of the order–disorder transition temperatures of compositionally symmetric samples. UV/ozone treatment following incorporation produces an ordered arrangement of oxide nanodots and simultaneously removes the block polymer template. Herein, we report the smallest particles (6 ± 1 nm) templated from a selective precursor insertion method to date using a block polymer sca...

Size-Tuned ZnO Nanocrucible Arrays for Magnetic Nanodot Synthesis via Atomic Layer Deposition-Assisted Block Polymer Lithography

Abstract: Low-temperature atomic layer deposition of conformal ZnO on a self-assembled block polymer lithographic template comprising well-ordered, vertically aligned cylindrical pores within a poly(styrene) (PS) matrix was used to produce nanocrucible templates with pore diameters tunable via ZnO thickness. Starting from a PS template with a hexagonal array of 30 nm diameter pores on a 45 nm pitch, the ZnO thickness was progressively increased to narrow the pore diameter to as low as 14 nm. Upon removal of the PS by heat treatment in air at 500 °C to form an array of size-tunable ZnO nanocrucibles, permalloy (Ni80Fe20) was evaporated at normal incidence, filling the pores and creating an overlayer. Argon ion beam milling was then used to etch back the overlayer (a Damascene-type process), leaving a well-ordered array of isolated ZnO nanocrucibles filled with permalloy nanodots. Microscopy and temperature-dependent magnetometry verified the diameter reduction with increasing ZnO thickness. The largest diameter (30 ...

Structure of Two-Compartment Hydrogels from Thermoresponsive ABC Triblock Terpolymers

Abstract: Aqueous dispersions of a poly(ethylene-alt-propylene)-b-poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PON) triblock terpolymer with block molecular weights of 3 000–25 000–10 000 and polymer concentrations ranging from 1 to 5 wt % were investigated at several temperatures from 25 to 55 °C using cryogenic scanning electron microscopy (cryo-SEM), cryogenic transmission electron microscopy (cryo-TEM), and small-angle neutron scattering (SANS). The cryo-SEM and cryo-TEM micrographs revealed that PON triblock terpolymer self-assembled into spherical micelles with PEP cores and PEO–PNIPAm coronae at room temperature and subsequently formed a two-compartment micellar network consisting of distinct spherical PEP and PNIPAm cores upon heating above the critical gelation temperature (42 °C). The formation of two discrete spherical PEP and PNIPAm hydrophobic domains was supported by detailed SANS analysis of the PON triblock samples in D2O, as the resulting intensity profiles can be successfully fitted using a...

Well-Ordered Nanoporous ABA Copolymer Thin Films via Solvent Vapor Annealing, Homopolymer Blending, and Selective Etching of ABAC Tetrablock Terpolymers

Abstract: Solvent vapor annealing treatments are used to control the orientation of nanostructures produced in thin films of a poly(styrene)-block-poly(isoprene)-block-poly(styrene)-block-poly((±)-lactide) (PS–PI–PS–PLA) and its blends with PLA homopolymer. The PS–PI–PS–PLA tetrablock terpolymer, previously determined to adopt a core(PLA)–shell(PS) cylindrical morphology in the bulk, gave perpendicular alignment of PLA cylinders over a limited range of thicknesses using a mixed solvent environment of tetrahydrofuran and acetone. On the other hand, perpendicular alignment was achieved regardless of film thickness by inclusion of 5 wt % homopolymer PLA in the PS–PI–PS–PLA tetrablock. Tapping mode atomic force microscopy (AFM) was used to visualize film surface morphologies. Subsequent reactive ion etching (RIE) and basic hydrolysis of PLA produced 15 nm pores in a PS–PI–PS triblock thin film matrix. Nanoporosity was confirmed by scanning electron microscopy (SEM) images and the vertical continuity of pores was confir...

Poly(beta-methyl-delta-valerolactone) block polymers

Abstract: Block copolymers include a poly β-methyl-δ-valerolactone (PMVL) block. The PMVL blocks can be formed from biosynthesized β-methyl-δ-valero lactone (MVL). The block copolymers can include hard blocks. The block copolymers can be thermoplastic elastomers.

Polymères séquencés de poly(bêta-méthyl-delta-valérolactone)

Abstract: L'invention concerne des copolymeres sequences comprenant un bloc poly β-methyl-δ-valerolactone (PMVL). Les blocs PMVL peuvent etre formes a partir de β-methyl-δ-valerolactone (MVL) bio-synthetisee. Les copolymeres sequences peuvent comprendre des blocs durs. Les copolymeres sequences peuvent etre des elastomeres thermoplastiques.