Showing papers by "Marc A. Hillmyer published in 2017"

50th Anniversary Perspective: There Is a Great Future in Sustainable Polymers

Abstract: It is likely that a half-century ago even enthusiastic and optimistic proponents of the synthetic polymer industry (Mr. McGuire included) could not have predicted the massive scale on which synthetic polymers would be manufactured and used today. Ultimately, the future success of this industry will rely on the development of sustainable polymers—materials derived from renewable feedstocks that are safe in both production and use and that can be recycled or disposed of in ways that are environmentally innocuous. Meeting these criteria in an economical manner cannot be achieved without transformative basic research that is the hallmark of this journal. In this Perspective we highlight five research topics—the synthesis of renewable monomers and of degradable polymers, the development of chemical recycling strategies, new classes of reprocessable thermosets, and the design of advanced catalysts—that we believe will play a vital role in the development of sustainable polymers. We also offer our outlook on sev...

Highly active zinc catalyst for the controlled polymerization of lactide.

Abstract: We report the preparation, structural characterization, and detailed lactide polymerization behavior of a new Zn(II) alkoxide complex, (L(1)ZnOEt)(2) (L(1) = 2,4-di-tert-butyl-6-{[(2'-dimethylaminoethyl)methylamino]methyl}phenolate). While an X-ray crystal structure revealed the complex to be dimeric in the solid state, nuclear magnetic resonance and mass spectrometric analyses showed that the monomeric form L(1)ZnOEt predominates in solution. The polymerization of lactide using this complex proceeded with good molecular weight control and gave relatively narrow molecular weight distribution polylactide, even at catalyst loadings of <0.1% that yielded M(n) as high as 130 kg mol(-)(1). The effect of impurities on the molecular weight of the product polymers was accounted for using a simple model. Detailed kinetic studies of the polymerization reaction enabled integral and nonintegral orders in L(1)ZnOEt to be distinguished and the empirical rate law to be elucidated, -d[LA]/dt = k(p)[L(1)ZnOEt][LA]. These studies also showed that L(1)ZnOEt polymerizes lactide at a rate faster than any other Zn-containing system reported previously. This work provides important mechanistic information pertaining to the polymerization of lactide and other cyclic esters by discrete metal alkoxide complexes.

The promise of plastics from plants

Abstract: Polymers protect us from the elements, increase the fuel efficiency of cars, protect food from pathogens, help cure disease, and enable renewable-energy technologies. To promote, foster, and enable a sustainable society, we need polymers. Yet polymers can also create serious environmental challenges. Nearly all plastic packaging produced—more than 80 billion kg annually—originates from fossil resources and is disposed of after a relatively short period of use ( 1 , 2 ). An increasing fraction of plastic is recycled or incinerated to recover energy, but most ends up in landfills, littering cities or landscapes, and in the oceans ( 3 ). New recycling concepts ( 4 ), clean incineration, and the development of polymers that can rapidly degrade ( 5 ) will be key to addressing these problems. Shifting from petrochemical feedstocks to renewable resources—making plastics from plants—can also rectify some environmental challenges associated with petrochemical extraction and render plastics production sustainable (see the figure).

Thermal processing of diblock copolymer melts mimics metallurgy

Abstract: Small-angle x-ray scattering experiments conducted with compositionally asymmetric low molar mass poly(isoprene)-b-poly(lactide) diblock copolymers reveal an extraordinary thermal history dependence. The development of distinct periodic crystalline or aperiodic quasicrystalline states depends on how specimens are cooled from the disordered state to temperatures below the order-disorder transition temperature. Whereas direct cooling leads to the formation of documented morphologies, rapidly quenched samples that are then heated from low temperature form the hexagonal C14 and cubic C15 Laves phases commonly found in metal alloys. Self-consistent mean-field theory calculations show that these, and other associated Frank-Kasper phases, have nearly degenerate free energies, suggesting that processing history drives the material into long-lived metastable states defined by self-assembled particles with discrete populations of volumes and polyhedral shapes.

Conformational Asymmetry and Quasicrystal Approximants in Linear Diblock Copolymers

Abstract: Small angle x-ray scattering experiments on three model low molar mass diblock copolymer systems containing minority polylactide and majority hydrocarbon blocks demonstrate that conformational asymmetry stabilizes the Frank-Kasper $\ensuremath{\sigma}$ phase Differences in block flexibility compete with space filling at constant density inducing the formation of polyhedral shaped particles that assemble into this low symmetry ordered state with local tetrahedral coordination These results confirm predictions from self-consistent field theory that establish the origins of symmetry breaking in the ordering of block polymer melts subjected to compositional and conformational asymmetry

Structural effects on the reprocessability and stress relaxation of crosslinked polyhydroxyurethanes

Abstract: Crosslinked polyhydroxyurethane (PHU) networks synthesized from difunctional six-membered cyclic carbonates and triamines are reprocessable at elevated temperatures through transcarbamoylation reactions. Here we study the structural effects on reprocessability and stress relaxation in crosslinked PHUs. Crosslinked PHUs derived from bis(five-membered cyclic carbonates) are shown to decompose at temperatures needed for reprocessing, likely via initial reversion of the PHU linkage and subsequent side reactions of the liberated amine and cyclic carbonate. Therefore, several six-membered cyclic carbonate-based PHUs with varying polymer backbones and crosslink densities were synthesized. These networks show large differences in the Arrhenius activation energy of stress relaxation (from 99 to 136 kJ/mol) that depend on the network structure, suggesting that transcarbamoylation reactions may be highly affected by both chemical and mechanical effects. Furthermore, all crosslinked PHUs derived from six-membered cyclic carbonates show mechanical properties typical of thermoset polymers, but recovered as much as 80% of their as-synthesized tensile properties after elevated temperature compression molding. These studies provide significant insight into factors affecting the reprocessability of PHUs and inform design criteria for the future synthesis of sustainable and repairable crosslinked PHUs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44984.

Robust Polymer Electrolyte Membranes with High Ambient-Temperature Lithium-Ion Conductivity via Polymerization-Induced Microphase Separation

Abstract: Mechanically robust polymer electrolyte membranes (PEMs) exhibiting high ionic conductivity at ambient temperature are a prerequisite for next-generation electrochemical devices. We utilized a polymerization-induced microphase separation (PIMS) strategy to prepare nanostructured materials comprising continuous conducting nanochannels intertwined with a mechanically and thermally robust cross-linked polymeric framework. Addition of succinonitrile (SN) rendered the poly(ethylene oxide)/lithium (Li) salt conducting domains completely amorphous, resulting in outstanding conductivities (∼0.35 mS/cm) at 30 °C. Concurrently, a densely cross-linked polystyrene framework provided mechanical robustness (modulus E′ ≈ 0.3 GPa at 30 °C) to the hybrid material. This work highlights a facile, single-pot strategy involving a homogeneous liquid reaction precursor that yields a high-performance ion-conducting membrane attractive for lithium-battery applications.

Tuning Mesoporosity in Cross-Linked Nanostructured Thermosets via Polymerization-Induced Microphase Separation

Abstract: Using the synthetic approach of polymerization-induced microphase separation (PIMS), we prepared cocontinuous and cross-linked nanostructured monoliths from bulk polymerizations of styrene and divinylbenzene (DVB) in the presence of polylactide macro-chain-transfer agents (PLA-CTAs). The resulting monolithic precursors were converted to cross-linked mesoporous materials following hydrolytic degradation of the PLA domain, the morphology and porosity of which were characterized through a combination of small-angle X-ray scattering, scanning electron microscopy, and nitrogen sorption experiments. This report highlights the concept, functionality, and limitations of PIMS for the generation of mesoporous materials through variation of reaction parameters found to strongly influence the porous properties of the matrix: the cross-linker-to-monomer ratio, reaction temperature, molar mass and mass fraction of PLA-CTA, and the reactivity of the DVB isomer. Increases in the cross-linker-to-monomer ratio (≥40 mol % D...

Enhanced Performance of Blended Polymer Excipients in Delivering a Hydrophobic Drug through the Synergistic Action of Micelles and HPMCAS.

Abstract: Blends of hydroxypropyl methylcellulose acetate succinate (HPMCAS) and dodecyl (C12)-tailed poly(N-isopropylacrylamide) (PNIPAm) were systematically explored as a model system to dispense the active ingredient phenytoin by rapid dissolution, followed by the suppression of drug crystallization for an extended period. Dynamic and static light scattering revealed that C12-PNIPAm polymers, synthesized by reversible addition–fragmentation chain-transfer polymerization, self-assembled into micelles with dodecyl cores in phosphate-buffered saline (PBS, pH 6.5). A synergistic effect on drug supersaturation was documented during in vitro dissolution tests by varying the blending ratio, with HPMACS primarily aiding in rapid dissolution and PNIPAm maintaining supersaturation. Polarized light and cryogenic transmission electron microscopy experiments revealed that C12-PNIPAm micelles maintain drug supersaturation by inhibiting both crystal nucleation and growth. Cross-peaks between the phenyl group of phenytoin and t...

Degradable Thermosets Derived from an Isosorbide/Succinic Anhydride Monomer and Glycerol

Abstract: Isosorbide is a renewable chemical of considerable interest as a monomer and monomer precursor due to its potential use in replacements for fossil-fuel derived polymers. In the present study, a facile microwave-assisted condensation of isosorbide with succinic anhydride was developed that dramatically reduced the reaction time. The resulting isosorbide disuccinic acid derivative (I-S-2) was polymerized under solvent-free conditions with glycerol to produce a renewable, cross-linked polyester with high modulus and appreciable thermal stability. Inclusion of 13 wt % or more of low molar mass hydroxy-telechelic poly(ethylene oxide) (PEO) (Mn = 300 g/mol) produced materials with a notable decrease in modulus and glass transition temperature. Degradation studies at 50 °C in acidic and basic solutions demonstrated the ability of the I-S-2 thermosets to be readily hydrolyzable. Furthermore, the resulting aqueous degradation solutions can be concentrated and reheated to produce new materials, albeit with a reduct...

Impact of Polymer Excipient Molar Mass and End Groups on Hydrophobic Drug Solubility Enhancement

Abstract: Solubility-enhancing amorphous solid dispersions are used in the oral delivery of hydrophobic, crystallizable drugs. Effective solid dispersion excipients enable high supersaturation drug concentrations and limit crystallization of the dissolved drug over extended times. We prepared poly(N-isopropylacrylamide)-based excipients of varying molar mass and with various end group identities, and examined their ability to improve the aqueous solubility of the Biopharmaceutical Class System Class II drug, phenytoin. Solid dispersions of these excipients and phenytoin were prepared at 10 wt % drug loading. Performance depended largely on the tendency of the polymer excipient to form micellar aggregates in aqueous buffer. We present several systems that achieved significant improvement of phenytoin solubility, with no indication of drug crystallization over 6 h. This is among the highest enhancement factors seen for phenytoin to date, and the success of these systems is ascribed to the added stability of these “se...

Nanoporous Thermosets with Percolating Pores from Block Polymers Chemically Fixed above the Order–Disorder Transition

Abstract: A lamellar diblock polymer combining a cross-linkable segment with a chemically etchable segment was cross-linked above its order–disorder temperature (TODT) to kinetically trap the morphology associated with the fluctuating disordered state. After removal of the etchable block, evaluation of the resulting porous thermoset allows for an unprecedented experimental characterization of the trapped disordered phase. Through a combination of small-angle X-ray scattering, nitrogen sorption, scanning electron microscopy, and electron tomography experiments we demonstrate that the nanoporous structure exhibits a narrow pore size distribution and a high surface to volume ratio and is bicontinuous over a large sample area. Together with the processability of the polymeric starting material, the proposed system combines attractive attributes for many advanced applications. In particular, it was used to design new composite membranes for the ultrafiltration of water.

Direct Observation of Nanostructures during Aqueous Dissolution of Polymer/Drug Particles

Abstract: To elucidate the aqueous solubility enhancement mechanism of solid dispersions (SDs), metastable blends of an active pharmaceutical ingredient (API) and a polymer excipient, we investigated the dissolution of hydroxypropyl methylcellulose acetate succinate (HPMCAS) SDs in phosphate buffered saline (PBS). Two hydrophobic active pharmaceutical agents, phenytoin and probucol, were employed at loadings of 10, 25, and 50 wt % relative to polymer. Light scattering measurements of HPMCAS solutions showed that the polymer itself formed a mixture of ∼10 and ∼100 nm sized structures (attributed to linear and covalently coupled polymer chains, respectively) in both tetrahydrofuran and PBS. The measurements also revealed that PBS is a poor solvent for HPMCAS at and below 37 °C, potentially inducing the polymer to associate with itself or other hydrophobic species in solution. During in vitro dissolution of HPMCAS SDs—containing either phenytoin or probucol as the API—the polymer and hydrophobic drug formed <100 nm am...

Polymer Day: Outreach Experiments for High School Students

Abstract: We present a collection of hands-on experiments that collectively teach precollege students fundamental concepts of polymer synthesis and characterization. These interactive experiments are performed annually as part of an all-day outreach event for high school students that can inform the development of ongoing polymer education efforts in a university setting. The Advanced Polymer Synthesis experiment aims to introduce broad concepts of polymer synthesis. Techniques such as ring-opening polymerization are explained and demonstrated. The Block Polymer Micellization experiment extends this idea to block polymers for drug delivery applications. Students are taught the idea of self-assembly and prepare micelles to encapsulate β-carotene in water with flash nanoprecipitation. In terms of materials characterization, the vast physical properties space of polymers is explored. The Happy–Sad Spheres experiment provides an interactive demonstration of the glass transition temperature, while the Polymer Swelling/R...

Oxidatively Stable Polyolefin Thermoplastics and Elastomers for Biomedical Applications

Abstract: Statistical copolymers were prepared by the Ring Opening Metathesis coPolymerization (ROMP) of (Z)-5,5-dimethylcyclooct-1-ene and cis-cyclooctene. Subsequent hydrogenation yielded poly(ethylene-co-isobutylene) (PEIB) materials. The feed ratio of the comonomers controls the degree of branching and resulting thermal and mechanical properties of the PEIB samples. Oxidative degradation studies, conducted under accelerated in vitro conditions were used to assess and predict their long-term biostability. Relative to commercial poly(ether urethanes) and a structurally similar polyolefin, poly(ethylene-co-1-butylene), the PEIB samples showed much better oxidative resistance. The facile synthesis, improved stability, and excellent mechanical performance of these PEIB materials bode well for their use in biomedical applications that require long-term biostability.

Morphological Consequences of Frustration in ABC Triblock Polymers

Abstract: Three poly(styrene)-block-poly(isoprene)-block-poly(lactide) (PS-b-PI-b-PLA, SIL) triblock terpolymers were synthesized and characterized in the bulk and as thin films. The pronounced incompatibility of the covalently connected PI and PLA led to significant frustration and the tendency to minimize their intermaterial dividing surface area. This resulted in the formation of a core–shell cylinder morphology with exaggerated nonconstant mean curvature from triblock polymers with equal block volume fractions rather than the more typical lamellar morphology. The effect of frustration was magnified in thin films by both confinement and interfacial interactions such that the PI domains became discontinuous. Self-consistent field theory (SCFT) calculations emphasize that the marked difference in the PS/PI and PI/PLA interaction parameters promotes the formation of nonlamellar morphologies. However, SCFT predicts that lamellar morphology is more stable than the observed cylindrical morphology, demonstrating a limi...

Intrinsically Hierarchical Nanoporous Polymers via Polymerization-Induced Microphase Separation

Abstract: The synthesis of microporous polymers generally requires postpolymerization modification via hyper-cross-linking to trap the polymeric network in a state with high void volume An alternative approach utilizes rigid, sterically demanding monomers to inhibit efficient packing, thus leading to a high degree of free volume between polymer side groups and main chains Herein we combine polymers of intrinsic microporosity with polymerization-induced microphase separation (PIMS), a versatile methodology for the synthesis of nanostructured materials that can be rendered mesoporous Copolymerization of various styrenic monomers with divinylbenzene in the presence of a poly(lactide) terminated with a chain-transfer agent (PLA-CTA) results in kinetic trapping of a microphase-separated state Subsequent etching of PLA provides a bicontinuous mesoporous network Using equilibrium and kinetic nitrogen sorption experiments as well as positron annihilation lifetime spectroscopy (PALS), we demonstrate that variations in

Self-Supporting, Hydrophobic, Ionic Liquid-Based Reference Electrodes Prepared by Polymerization-Induced Microphase Separation

Abstract: Interfaces of ionic liquids and aqueous solutions exhibit stable electrical potentials over a wide range of aqueous electrolyte concentrations This makes ionic liquids suitable as bridge materials that separate in electroanalytical measurements the reference electrode from samples with low and/or unknown ionic strengths However, methods for the preparation of ionic liquid-based reference electrodes have not been explored widely We have designed a convenient and reliable synthesis of ionic liquid-based reference electrodes by polymerization-induced microphase separation This technique allows for a facile, single-pot synthesis of ready-to-use reference electrodes that incorporate ion conducting nanochannels filled with either 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-dodecyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide as ionic liquid, supported by a mechanically robust cross-linked polystyrene phase This synthesis procedure allows for the straightforward design of va

Tricontinuous Nanostructured Polymers via Polymerization-Induced Microphase Separation

Abstract: Nanostructured tricontinuous block polymers allow for the preparation of single-component materials that combine multiple properties. We demonstrate the synthesis of a mesoporous material from the selective orthogonal etching of a microphase-separated tricontinuous block polymer precursor. Using the synthetic approach of polymerization-induced microphase separation (PIMS), divinylbenzene (DVB) is polymerized from a mixture of poly(isoprene) (PI) and poly(lactide) (PLA) macro-chain transfer agents. In the PIMS process in situ cross-linking by the DVB arrests structural coarsening, resulting in a disordered block polymer morphology that we posit exhibits three nonintersecting continuous domains. Selective etching of the PI domains by olefin cross metathesis and PLA domains by hydrolytic degradation produces a mesoporous polymer with two independent pore networks arising from the different etch mechanisms.

Synthesis and utility of ethylene (meth)acrylate copolymers prepared by a tandem ring-opening polymerization hydrogenation strategy

Abstract: One new and one established functional cyclooctene were prepared and (co)polymerized using ring-opening metathesis polymerization. The resulting polymers were hydrogenated to yield the corresponding functional polyolefins that were structurally equivalent to copolymers of ethylene and either methyl methacrylate, t-butyl acrylate, or acrylic acid after deprotection. The copolymers that incorporate methyl methacrylate into the backbone were used as compatibilizers for poly(methyl methacrylate)/polyethylene blends. The copolymers that incorporate t-butyl acrylate into the backbone yielded elastomers that could be thermally crosslinked. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3117–3126

Recovery of monomer from polyurethane materials by depolymerization

Abstract: Methods for recovering monomers from polymers, such as polyurethanes (including thermoset polyurethanes) include heating the polymer to depolymerize the polymer and release the monomer. The monomer may be directly recovered. The polymer may include a poly(β-methyl-δ-valerolactone) (PMVL) block and the monomer recovered may be β-methyl-δ-valerolactone (MVL).

Graft copolymers based on polyolefin backbone and methacrylate side chains

Abstract: The present application is directed to a graft copolymer comprising in the backbone at least one segment having repeating units obtainable by ring-opening metathesis polymerization (ROMP) of an optionally substituted cycloalkene and at least one segment comprising repeating units obtainable by atom transfer radical polymerization (ATRP) of a (meth)acrylate. The corresponding graft copolymer is highly suitable for use as an oil additive in internal combustion engines, in particular, in combustion engines which are operated for longer periods of time at substantially constant operating temperatures.

Copolymères greffés à base d'un squelette de polyoléfine et de chaînes latérales de méthacrylate

Abstract: La presente invention concerne un copolymere greffe comprenant dans le squelette au moins un segment ayant des unites repetitives pouvant etre obtenues par polymerisation par metathese a ouverture de cycle (ROMP) d'un cycloalcene eventuellement substitue et au moins un segment comprenant des unites repetitives pouvant etre obtenues par polymerisation radicalaire par transfert d'atome (ATRP) d'un (meth)acrylate. Le copolymere greffe correspondant est extremement approprie pour etre utilise comme additif d'huile dans des moteurs a combustion interne, en particulier dans des moteurs a combustion qui fonctionnent pendant des durees prolongees a des temperatures de fonctionnement sensiblement constantes.

Methods for making renewable and chemically recyclable crosslinked polyester elastomers

Abstract: A method includes reacting a polymer derived from a lactone with a cyclic carbonate compound comprising 2 to 5 cyclic carbonate moieties and a catalyst to form a crosslinked polylactone elastomer.