Morphology of Isotactic Polypropylene–Polyethylene Block Copolymers Driven by Controlled Crystallization

A study of the morphology of diblock copolymers composed of two crystalline blocks of isotactic polypropylene (iPP) and polyethylene (PE) is shown. The samples form phase-separated structures in the melt because of the incompatibility between iPP and PE blocks. Cylindrical PE microdomains are visible at room temperature in the sample with a PE volume fraction of 26%, rapidly quenched from the melt in liquid nitrogen. In the quenched sample, PE crystallizes inside the PE cylindrical microdomains, whereas crystals of iPP are not visible in the iPP domains because the quenching prevents crystallization of the lamellar α form. Less rapid cooling of the melt produces, instead, breakout crystallization, where the phase-separated structure of the melt is destroyed by the slow crystallization of the α form of iPP and of PE. The succession of crystallization of iPP and PE and the resulting final morphology have been analyzed by inducing selective and different orientations of iPP and PE crystals through epitaxial crystallization onto the benzoic acid (BA) crystal substrate. Epitaxy produces oriented crystallization of iPP and PE, with a unique alignment of PE lamellar crystals and a double orientation of iPP crystals on to the (001) exposed face of BA. Epitaxy destroys the phase-separated structure of the melt and induces the formation of ordered lamellar nanostructures with alternated layers of iPP and PE, whose orientation is defined by the alignment of PE or iPP crystals, which, in turn, is determined by epitaxy. The results indicate that crystalline block copolymers offer the opportunity to create nanoscale patterns on thin films and improve the possibility of controlling the microstructure of block copolymers and the alignment of microdomains by controlling the crystallization process

Universal Relationship between Conductivity and Solvation-Site Connectivity in Ether-Based Polymer Electrolytes

We perform a joint experimental and computational study of ion transport properties in a systematic set of linear polyethers synthesized via acyclic diene metathesis (ADMET) polymerization. We measure ionic conductivity, σ, and glass transition temperature, T_g, in mixtures of polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. While T_g is known to be an important factor in the ionic conductivity of polymer electrolytes, recent work indicates that the number and proximity of lithium ion solvation sites in the polymer also play an important role, but this effect has yet to be systematically investigated. Here, adding aliphatic linkers to a poly(ethylene oxide) (PEO) backbone lowers T_g and dilutes the polar groups; both factors influence ionic conductivity. To isolate these effects, we introduce a two-step normalization scheme. In the first step, Vogel–Tammann–Fulcher (VTF) fits are used to calculate a temperature-dependent reduced conductivity, σ_r(T), which is defined as the conductivity of the electrolyte at a fixed value of T – T_g. In the second step, we compute a nondimensional parameter f_(exp), defined as the ratio of the reduced molar conductivity of the electrolyte of interest to that of a reference polymer (PEO) at a fixed salt concentration. We find that f_(exp) depends only on oxygen mole fraction, x_0, and is to a good approximation independent of temperature and salt concentration. Molecular dynamics simulations are performed on neat polymers to quantify the occurrences of motifs that are similar to those obtained in the vicinity of isolated lithium ions. We show that f_(exp) is a linear function of the simulation-derived metric of connectivity between solvation sites. From the relationship between σ_r and f_(exp) we derive a universal equation that can be used to predict the conductivity of ether-based polymer electrolytes at any salt concentration and temperature

Trials and tribulations of designing multitasking catalysts for olefin/thiophene block copolymerizations

Block copolymers containing both insulating and conducting segments have been shown to exhibit improved charge transport properties and air stability. Nevertheless, their syntheses are challenging, relying on multiple post‐polymerization functionalization reactions and purifications. A simpler approach would be to synthesize the block copolymer in one pot using the same catalyst to enchain both monomers via distinct mechanisms. Such multitasking polymerization catalysts are rare, however, due to the challenges of finding a single catalyst that can mediate living, chain‐growth polymerizations for each monomer under similar conditions. Herein, a diimine‐ligated Ni catalyst is evaluated and optimized to produce block copolymer containing both 1‐pentene and 3‐hexylthiophene. The reaction mixture also contains both homopolymers, suggesting catalyst dissociation during and/or after the switch in mechanisms. Experimental and theoretical studies reveal a high energy switching step coupled with infrequent catalyst dissociation as the culprits for the low yield of copolymer. Combined, these studies highlight the challenges of identifying multitasking catalysts, and suggest that further tuning the reaction conditions (e.g., ancillary ligand structure and/or metal) is warranted for this specific copolymerization. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 132–137Block copolymers containing insulating segments (derived from 1‐pentene) and conducting segments (derived from 3‐hexylthiophene) are synthesized in one pot using a single multitasking catalyst. Notably, this process requires different enchainment mechanisms (coordination/insertion vs. cross‐coupling) mediated by the same precatalyst. Nevertheless, the block copolymer is the minor product due to a slow switching step between the mechanisms coupled with catalyst dissociation from the polymer chain.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139919/1/pola28885_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139919/2/pola28885.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139919/3/pola28885-sup-0001-suppinfo.pd

Unraveling Substituent Effects on the Glass Transition Temperatures of Biorenewable Polyesters

Converting biomass-based feedstocks into polymers not only reduces our reliance on fossil fuels, but also furnishes multiple opportunities to design biorenewable polymers with targeted properties and functionalities. Here we report a series of high glass transition temperature (Tg up to 184 °C) polyesters derived from sugar-based furan derivatives as well as a joint experimental and theoretical study of substituent effects on their thermal properties. Surprisingly, we find that polymers with moderate steric hindrance exhibit the highest Tg values. Through a detailed Ramachandran-type analysis of the rotational flexibility of the polymer backbone, we find that additional steric hindrance does not necessarily increase chain stiffness in these polyesters. We attribute this interesting structure-property relationship to a complex interplay between methylinduced steric strain and the concerted rotations along the polymer backbone. We believe that our findings provide key insight into the relationship between structure and thermal properties across a range of synthetic polymers

Universal Relationship between Conductivity and Solvation-Site Connectivity in Ether-Based Polymer Electrolytes

We perform a joint experimental and computational study of ion transport properties in a systematic set of linear polyethers synthesized via acyclic diene metathesis (ADMET) polymerization. We measure ionic conductivity, σ, and glass transition temperature, T_g, in mixtures of polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. While T_g is known to be an important factor in the ionic conductivity of polymer electrolytes, recent work indicates that the number and proximity of lithium ion solvation sites in the polymer also play an important role, but this effect has yet to be systematically investigated. Here, adding aliphatic linkers to a poly(ethylene oxide) (PEO) backbone lowers T_g and dilutes the polar groups; both factors influence ionic conductivity. To isolate these effects, we introduce a two-step normalization scheme. In the first step, Vogel–Tammann–Fulcher (VTF) fits are used to calculate a temperature-dependent reduced conductivity, σ_r(T), which is defined as the conductivity of the electrolyte at a fixed value of T – T_g. In the second step, we compute a nondimensional parameter f_(exp), defined as the ratio of the reduced molar conductivity of the electrolyte of interest to that of a reference polymer (PEO) at a fixed salt concentration. We find that f_(exp) depends only on oxygen mole fraction, x_0, and is to a good approximation independent of temperature and salt concentration. Molecular dynamics simulations are performed on neat polymers to quantify the occurrences of motifs that are similar to those obtained in the vicinity of isolated lithium ions. We show that f_(exp) is a linear function of the simulation-derived metric of connectivity between solvation sites. From the relationship between σ_r and f_(exp) we derive a universal equation that can be used to predict the conductivity of ether-based polymer electrolytes at any salt concentration and temperature

Optimizing Ion Transport in Polyether-Based Electrolytes for Lithium Batteries

We report on the synthesis of poly(diethylene oxide-alt-oxymethylene), P(2EO-MO), via cationic ring-opening polymerization of the cyclic ether monomer, 1,3,6-trioxocane. We use a combined experimental and computational approach to study ion transport in electrolytes comprising mixtures of P(2EO-MO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt. Mixtures of poly(ethylene oxide) (PEO) and LiTFSI are used as a baseline. The maximum ionic conductivities, σ, of P(2EO-MO) and PEO electrolytes at 90 °C are 1.1 × 10^(–3) and 1.5 × 10^(–3) S/cm, respectively. This difference is attributed to the T_g of P(2EO-MO)/LiTFSI (−12 °C), which is significantly higher than that of PEO/LiTFSI (−44 °C) at the same salt concentration. Self-diffusion coefficients measured using pulsed-field gradient NMR (PFG-NMR) show that both Li+ and TFSI– ions diffuse more rapidly in PEO than in P(2EO-MO). However, the NMR-based cation transference number in P(2EO-MO) (0.36) is approximately twice that in PEO (0.19). The transference number measured by the steady-state current technique, t_(+,ss), in P(2EO-MO) (0.20) is higher than in PEO (0.08) by a similar factor. We find that the product σt_(+,ss) is greater in P(2-EO-MO) electrolytes; thus, P(2EO-MO) is expected to sustain higher steady-state currents under dc polarization, making it a more efficacious electrolyte for battery applications. Molecular-level insight into the factors that govern ion transport in our electrolytes was obtained using MD simulations. These simulations show that the solvation structures around Li+ are similar in both polymers. The same is true for TFSI–. However, the density of Li+ solvation sites in P(2EO-MO) is double that in PEO. We posit that this is responsible for the observed differences in the experimentally determined transport properties of P(2EO-MO) and PEO electrolytes

Phenotypic screening reveals TNFR2 as a promising target for cancer immunotherapy.

Antibodies that target cell-surface molecules on T cells can enhance anti-tumor immune responses, resulting in sustained immune-mediated control of cancer. We set out to find new cancer immunotherapy targets by phenotypic screening on human regulatory T (Treg) cells and report the discovery of novel activators of tumor necrosis factor receptor 2 (TNFR2) and a potential role for this target in immunotherapy. A diverse phage display library was screened to find antibody mimetics with preferential binding to Treg cells, the most Treg-selective of which were all, without exception, found to bind specifically to TNFR2. A subset of these TNFR2 binders were found to agonise the receptor, inducing iκ-B degradation and NF-κB pathway signalling in vitro. TNFR2 was found to be expressed by tumor-infiltrating Treg cells, and to a lesser extent Teff cells, from three lung cancer patients, and a similar pattern was also observed in mice implanted with CT26 syngeneic tumors. In such animals, TNFR2-specific agonists inhibited tumor growth, enhanced tumor infiltration by CD8+ T cells and increased CD8+ T cell IFN-γ synthesis. Together, these data indicate a novel mechanism for TNF-α-independent TNFR2 agonism in cancer immunotherapy, and demonstrate the utility of target-agnostic screening in highlighting important targets during drug discovery.GW, BM, SG, JC-U, AS, AG-M, CB, JJ, RL, AJL, SR, RS, LJ, VV-A, RM and RWW were funded by MedImmune; JP and VB were funded by AstraZeneca PLC; JW, RSA-L and JB were funded by NIHR Cambridge Biomedical Research Centre and Kidney Research UK; JS and JF were funded by Retrogenix Ltd