Enumerating Finitary Processes.

We show how to efficiently enumerate a class of finite-memory stochastic processes using the causal representation of ϵ-machines. We characterize ϵ-machines in the language of automata theory and adapt a recent algorithm for generating accessible deterministic finite automata, pruning this over-large class down to that of ϵ-machines. As an application, we exactly enumerate topological ϵ-machines up to eight states and six-letter alphabets.

Persistent Toughness and Heat Triggered Plasticization in Polylactide Modified with Poly(ethylene oxide)--poly(butylene oxide).

Poly(lactide) (PLA) is a promising biodegradable polymer with potential applications in single-use packaging. However, its use is limited by brittleness, and its biodegradability is restricted to industrial compost conditions due in part to an elevated glass transition temperature (). We previously showed that addition of a poly(ethylene-oxide)--poly(butylene oxide) diblock copolymer (PEO-PBO) forms macrophase-separated rubbery domains in PLA that can impart significant toughness at only 5 wt %.

Alkyl-Substituted Polycaprolactone Poly(urethane-urea)s as Mechanically Competitive and Chemically Recyclable Materials.

We report the mechanical performance and chemical recycling advantages of implementing alkyl-substituted poly(ε-caprolactones) (PCLs) as soft segments in thermoplastic poly(urethane-urea) (TPUU) materials. Poly(4-methylcaprolactone) (P4MCL) and poly(4-propylcaprolactone) (P4PrCL) were prepared, reacted with isophorone diisocyanate, and chain-extended with water to form TPUUs. The resulting materials' tensile properties were similar or superior to a commercially available polyester thermoplastic poly(urethane) and had superior elastic recovery properties compared to a PCL analogue due to the noncrystalline nature of P4MCL and P4PrCL.

Equilibrium phase behavior of gyroid-forming diblock polymer thin films.

Thin-film confinement of self-assembling block polymers results in materials with myriad potential applications-including membranes and optical devices-and provides design parameters for altering phase behavior that are not available in the bulk, namely, film thickness and preferential wetting. However, most research has been limited to lamella- and cylinder-forming polymers; three-dimensional phases, such as double gyroid (DG), have been observed in thin films, but their phase behavior under confinement is not yet well understood. We use self-consistent field theory to predict the equilibrium morphology of bulk-gyroid-forming AB diblock polymers under thin-film confinement.

Porous Melt Blown Poly(butylene terephthalate) Fibers with High Ductility and High-Temperature Structural Stability.

In this study, porous poly(butylene terephthalate) (PBT) fibers were produced by melt blowing cocontinuous blends of PBT and polystyrene (PS) and selectively extracting the interconnected PS domains. Small amounts of hydroxyl terminated PS additives that can undergo transesterification with the ester units in PBT were added to stabilize the cocontinuous structure during melt processing. The resulting fibers are highly ductile and display fine porous structural features, which persist at temperatures over 150 °C.

Boundary Frustration in Double-Gyroid Thin Films.

Self-consistent field theory for thin films of AB diblock polymers in the double-gyroid phase reveals that in the absence of preferential wetting of monomer species at the film boundaries, films with the (211) plane oriented parallel to the boundaries are more stable than other orientations, consistent with experimental results. This preferred orientation is explained in the context of boundary frustration. Specifically, the angle of intersection between the A/B interface and the film boundary, the wetting angle, is thermodynamically restricted to a narrow range of values.

Thermodynamics and morphology of linear multiblock copolymers at homopolymer interfaces.

Block copolymers at homopolymer interfaces are poised to play a critical role in the compatibilization of mixed plastic waste, an area of growing importance as the rate of plastic accumulation rapidly increases. Using molecular dynamics simulations of Kremer-Grest polymer chains, we have investigated how the number of blocks and block degree of polymerization in a linear multiblock copolymer impacts the interface thermodynamics of strongly segregated homopolymer blends, which is key to effective compatibilization. The second virial coefficient reveals that interface thermodynamics are more sensitive to block degree of polymerization than to the number of blocks.

Threading-the-Needle: Compatibilization of HDPE/PP blends with butadiene-derived polyolefin block copolymers.

Management of the plastic industry is a momentous challenge, one that pits enormous societal benefits against an accumulating reservoir of nearly indestructible waste. A promising strategy for recycling polyethylene (PE) and isotactic polypropylene (PP), constituting roughly half the plastic produced annually worldwide, is melt blending for reformulation into useful products. Unfortunately, such blends are generally brittle and useless due to phase separation and mechanically weak domain interfaces.

Biobased Copolymers via Cationic Ring-Opening Copolymerization of Levoglucosan Derivatives and ε-Caprolactone.

Simultaneous ring-opening copolymerization is a powerful strategy for the synthesis of highly functional copolymers from different types of cyclic monomers. Although copolymers are essential to the plastics industry, environmental concerns associated with current fossil-fuel-based synthetic polymers have led to an increasing interest in the use of renewable feedstock for polymer synthesis. Herein, we report a scalable synthetic platform to afford unique polysaccharides with different pendant functional groups from biomass-derived levoglucosan and ε-caprolactone via cationic ring-opening copolymerization (cROCOP).

Photochemically Induced Marangoni Patterning of Polymer Bilayers.

Surface-tension gradients created along a polymer film by patterned photochemical reactions are a powerful tool for creating surface topography. Here, we use mathematical modeling to explore a strategy for patterning photochemically inactive polymers by coupling a light-sensitive and light-insensitive polymer to form a polymer bilayer. The light-sensitive polymer forms the top layer, and the most dominant surface-tension gradients are introduced at the interface between this layer and air.

Dihydroxy Polyethylene Additives for Compatibilization and Mechanical Recycling of Polyethylene Terephthalate/Polyethylene Mixed Plastic Waste.

Polymer blend compatibilization is an attractive solution for mechanical recycling of mixed plastic waste because it can result in tough blends. In this work, hydroxy-telechelic polyethylene (HOPEOH) reactive additives were used to compatibilize blends of polyethylene terephthalate (PET) and linear low-density polyethylene (LLDPE). HOPEOH additives were synthesized with molar masses of 1-20 kg/mol by ring-opening metathesis polymerization of cyclooctene followed by catalytic hydrogenation.

Camphene as a Mild, Bio-Derived Porogen for Near-Ambient Processing and 3D Printing of Porous Thermoplastics.

Porous structures are ubiquitous in nature due to their advantageous mechanical and transport properties. These structures have inspired various synthetic porous polymer technologies, including lightweight structural materials and membranes. While many manufacturing processes have been developed to generate porous thermoplastics, these usually include hazardous processes, such as high pressures and temperatures, or chemical components.

Camphene-Assisted Fabrication of Free-Standing Lithium-Ion Battery Electrode Composites.

Free-standing electrode (FSE) architectures hold the potential to dramatically increase the gravimetric and volumetric energy density of lithium-ion batteries (LIBs) by eliminating the parasitic dead weight and volume associated with traditional metal foil current collectors. However, current FSE fabrication methods suffer from insufficient mechanical stability, electrochemical performance, or industrial adoptability. Here, we demonstrate a scalable camphene-assisted fabrication method that allows simultaneous casting and templating of FSEs comprising common LIB materials with a performance superior to their foil-cast counterparts.

Poly(2,3-Dihydrofuran): A Strong, Biorenewable, and Degradable Thermoplastic Synthesized via Room Temperature Cationic Polymerization.

Creation of strong and tough plastics from sustainable and biorenewable resources is a significant challenge in polymer science. This challenge is further complicated when attempting to make these materials using an economically viable process, which is often hindered by the production and availability of chemical feedstocks and the efficiency of the monomer synthesis. Herein, we report the synthesis and characterization of a strong thermoplastic made from 2,3-dihydrofuran (DHF), a monomer made in one step from 1,4-butanediol, a bioalcohol already produced on the plant scale.

Synthetic growth by self-lubricated photopolymerization and extrusion inspired by plants and fungi.

Many natural organisms, such as fungal hyphae and plant roots, grow at their tips, enabling the generation of complex bodies composed of natural materials as well as dexterous movement and exploration. Tip growth presents an exemplary process by which materials synthesis and actuation are coupled, providing a blueprint for how growth could be realized in a synthetic system. Herein, we identify three underlying principles essential to tip-based growth of biological organisms: a fluid pressure driving force, localized polymerization for generating structure, and fluid-mediated transport of constituent materials.

Controlling Surface Deformation and Feature Aspect Ratio in Photochemically Induced Marangoni Patterning of Polymer Films.

Thin liquid polymer films can be topographically patterned when polymer/air interfaces are deformed by surface-tension gradients. Toward this end, a recently developed method first photochemically patterns surface-tension gradients along a solid, flat polymer film. On heating to the liquid state, the film initially develops topography reflecting the patterned surface-tension gradients.

Stereoregular functionalized polysaccharides cationic ring-opening polymerization of biomass-derived levoglucosan.

We report the facile synthesis and characterization of 1,6-α linked functional stereoregular polysaccharides from biomass-derived levoglucosan cationic ring-opening polymerization (cROP). Levoglucosan is a bicyclic acetal with rich hydroxyl functionality, which can be synthetically modified to install a variety of pendant groups for tailored properties. We have employed biocompatible and recyclable metal triflate catalysts - scandium and bismuth triflate - for green cROP of levoglucosan derivatives, even at very low catalyst loadings of 0.

Structural Basis for the Different Mechanical Behaviors of Two Chemically Analogous, Carbohydrate-Derived Thermosets.

Two renewable, structurally analogous monomers, isosorbide undecenoate (IU) and glucarodilactone undecenoate (GDLU) reacted with pentaerythritol tetrakis(3-mercaptopropionate) (PETT) via thiol-ene photopolymerization to form IU-PETT and GDLU-PETT thermosets. Despite their chemical similarity, uniaxial tensile testing showed that GDLU-PETT exhibited a strain-hardening behavior and is significantly tougher than IU-PETT. To understand this observation, in situ tensile testing and wide-angle X-ray scattering experiments (WAXS) were conducted.

Porous Fibers Templated by Melt Blowing Cocontinuous Immiscible Polymer Blends.

We report a scalable melt blowing method for producing porous nonwoven fibers from model cocontinuous polystyrene/high-density polyethylene polymer blends. While conventional melt compounding of cocontinuous blends typically produces domain sizes ∼1-10 μm, melt blowing these blends into fibers reduces those dimensions up to 35-fold and generates an interpenetrating domain structure. Inclusion of ≤1 wt % of a block copolymer compatibilizer in these blends crucially enables access to smaller domain sizes in the fibers by minimizing thermodynamically-driven blend coarsening inherent to cocontinuous blends.

Linear, Graft, and Beyond: Multiblock Copolymers as Next-Generation Compatibilizers.

Properly addressing the global issue of unsustainable plastic waste generation and accumulation will require a confluence of technological breakthroughs on various fronts. Mechanical recycling of plastic waste into polymer blends is one method expected to contribute to a solution. Due to phase separation of individual components, mechanical recycling of mixed polymer waste streams generally results in an unsuitable material with substantially reduced performance.

Defining the Macromolecules of Tomorrow through Synergistic Sustainable Polymer Research.

Transforming how plastics are made, unmade, and remade through innovative research and diverse partnerships that together foster environmental stewardship is critically important to a sustainable future. Designing, preparing, and implementing polymers derived from renewable resources for a wide range of advanced applications that promote future economic development, energy efficiency, and environmental sustainability are all central to these efforts. In this contribution, we take a comprehensive, integrated approach to summarize important and impactful contributions to this broad research arena.

Enhanced Polyester Degradation through Transesterification with Salicylates.

Polyesters constitute nearly 10% of the global plastic market, but most are essentially non-degradable under ambient conditions or in engineered environments. A range of degradable polyesters have been developed as more sustainable alternatives; however, limitations of practical degradability and scalability have hindered their viability. Here, we utilized transesterification approaches, including polymerization-transesterification, between a salicylate and a polyester to incorporate salicylate units into commercial polyester backbones.

Flexible Nanoporous Materials by Matrix Removal from Cylinder-Forming Diblock Copolymers.

We describe a straightforward self-assembly route to nanoporous materials derived from a hexagonally-packed cylinder (HEX) morphology of a polyisoprene--polylactide (PI--PLA) diblock copolymer, by thermal cross-linking of the minority PI domains followed by selective chemical etching of the PLA matrix. The resulting mechanically stable and porous samples defy the expectation that the remaining cylinders cannot yield a robust, integrated material upon matrix removal. Scanning electron microscopy imaging reveals that this unexpected structural integrity stems from the interconnected nanofibrils therein, reflecting topological defects at the grain boundaries of the parent polydomain HEX nanostructure.

Achieving Stable Patterns in Multicomponent Polymer Thin Films Using Marangoni and van der Waals Forces.

Liquid-air interfaces can be deformed by surface-tension gradients to create topography, a phenomenon useful for polymer film patterning. A recently developed method creates these gradients by photochemically patterning a solid polymer film. Heating the film to the liquid state leads to flow driven by the patterned surface-tension gradients, but capillary leveling and diffusion of surface-active species facilitate eventual dissipation of the topography.