Statistical or random copolymers of styrene (S) and 2-ethylhexyl acrylate (EHA) were previously reported to exhibit unusual glass transition breadth and facile self-healing over a broad composition range, and low levels of EHA in styrene-based polymers were shown to eliminate nanoconfinement effects on the glass transition temperature (T-g) in supported styrene-based polymer films. The present study demonstrates that these remarkable outcomes are also observed when 2-propylheptyl acrylate (PHA) is used as the comonomer, rather than EHA. Like EHA, PHA has a branched, alkyl side chain capable of undergoing van der Waals interactions that may result in interdigitation between two 2-propylheptyl side groups. Such interactions are associated with enhanced T-g breadth and facile self-healing character. 58/42 and 62/38 mol% S/PHA copolymers exhibit T-g breadths of 31 degrees C-32 degrees C, twice that of polystyrene (PS), and undergo 100% recovery after damage by room-temperature self-healing in time frames of 1-6 h. Relative to bulk PS homopolymer, supported PS films exhibit significant deviations in T-g from bulk response at 50-60 nm thickness and show a T-g reduction of similar to 10 degrees C in 15-nm-thick films. In contrast, 97/3 and 94/6 mol% S/PHA copolymers show no T-g confinement effect down to supported film thicknesses of 15-20 nm.

Statistical copolymers, also called random copolymers, of styrene (S) and 2-ethylhexyl acrylate (EHA) have recently been reported to exhibit unusual glass transition breadth and facile autonomous self-healing character over a broad composition range. Very low levels of EHA incorporated into styrene-based polymers have also been reported to eliminate the glass transition temperature (Tg)-confinement effect in supported styrene-based polymer films down to 15-20 nm thicknesses. Here, we show that these remarkable outcomes in S-based copolymers are not unique to EHA but are also present when 2-propylheptyl acrylate (PHA) is the comonomer. Like EHA, PHA has a branched, alkyl side chain capable of undergoing van der Waals interactions, which may result in interdigitation between 2-propylheptyl side groups on different chains. Such interactions are associated with enhanced Tg breadth and are considered the underlying cause of the facile self-healing character. 58/42 mol% and 62/38 mol% S/PHA copolymers exhibit Tg-breadths of 31-32 C, twice that of polystyrene (PS), and undergo 100% recovery after damage by room-temperature self-healing in time frames of 1 h and 6 h, respectively. Relative to bulk homo PS, supported PS films begin to exhibit significant deviations in Tg from bulk response at 50-60 nm thickness and show a Tg reduction of ~10 C in 15-nm-thick films. In contrast, 97/3 mol% and 94/6 mol% S/PHA copolymers show no Tg-confinement effect down to supported film thicknesses of 20 and 15 nm, respectively.

Statistical copolymers are commercially important because their properties can be tuned by comonomer selection and composition. Rubbery-state styrene (S)/n-butyl acrylate (nBA) copolymers have previously been reported to exhibit facile, autonomous self-healing over a narrow composition band (47/53 to 53/47 mol%). The need for a narrow composition band is explained by alternating comonomer sequences that accommodate interchain secondary bonding. It is hypothesized that copolymers that achieve interchain secondary bonding without alternating sequences can exhibit facile self-healing over a broad composition range. 2-ethylhexyl acrylate (EHA) is identified as yielding sequence-independent secondary bonding interactions. For these interactions it is tested experimentally by glass transition breadth in rubbery-state S/EHA copolymers, with S/n-hexyl acrylate (nHA) and S/nBA copolymers as controls. The n-alkyl acrylate random copolymers exhibit enhanced glass transition breadths over narrow composition bands that correspond to autonomous self-healing. In contrast, S/EHA copolymers exhibit much greater glass transition breadths than S/nHA and S/nBA copolymers at all compositions tested as well as self-healing of damage over a broad composition range with full tensile-property recovery, often in 3-10 h. Characterization of glass transition breadth may serve as a simple screening tool for identifying copolymers that exhibit broad-composition-range, facile, autonomous self-healing and contribute to polymer resilience and sustainability. 2-ethylhexyl acrylate (EHA) promotes facile autonomous self-healing in styrene/EHA random copolymers over a broad composition range. Because any two sufficiently close EHA units have the potential to interdigitate or similarly order, previous limitations of facile self-healing only being realized in approximate to 50/50 mol% styrene/acrylate copolymers are eliminated. Styrene/EHA copolymers exhibit unusually broad glass transitions due to the resulting secondary bonding. image

Sustainability and circularity are key issues facing the global polymer industry. The search for biodegradable and environmentally-friendly polymers that can replace conventional materials is a difficult challenge that has been met with limited success. Alternatives must be cost-effective, scalable, and provide equivalent performance. We report that latexes made by the conventional emulsion polymerization of vinyl acetate and functional vinyl ester monomers are efficient thickeners for consumer products and biodegrade in wastewater. This approach uses readily-available starting materials and polymerization is carried out in water at room temperature, in one pot, and generates negligible waste. Moreover, the knowledge that poly(vinyl ester)s are biodegradable will lead to the design of new green polymer materials.

The development of polymerization methods that installweak linksor degradable bonds in the backbone of otherwise all-carbon chainscould accelerate the design and commercialization of new classes ofrecyclable, upcyclable, or biodegradable polymers. Cyclic ketene acetalsincluding widely studied 2-methylene-1,3-dioxepane (MDO) can be usedas comonomers in conventional free-radical polymerizations to insertlabile ester bonds into addition polymer backbones. However, the keyobstacle in deploying MDO in water-borne, industrially relevant processesis hydrolysis of the monomer itself. Optimized conditions includingrelatively low temperatures, mildly alkaline pH, and consistent radicalflux lead to high in-process conversions, a rapid rate of polymerization,and a low degree of MDO hydrolysis. Although MDO hydrolysis competesstrongly with copolymerization, degradation can be minimized duringaqueous emulsion polymerization with vinyl acetate to give robustincorporations of & SIM;90% MDO. The methods and quantitative analysistools reported here provide principles for the copolymerization ofMDO in aqueous media and will drive innovations in the circular polymereconomy.

Over the past few decades, combinatorial methodologies have become very useful tools to understand and decouple the complexities of interfacial polymer adhesion. In this chapter, the importance and critical aspects of the high-throughput (HT) methodologies and the advances made in this field are described. Citing specific examples, this discussion highlights challenges in developing HT screening methods to characterize interfacial adhesion. Next, a typical combinatorial approach used to examine the complexities of structural adhesion is discussed. Specifically, an HT die shear test is used to characterize the shear strength of an adhesive. A testing workflow is proposed and the relationship between the die shear strength and the lap shear strength is validated. Critical aspects pertaining to the durability of adhesive bonds are then discussed. After considering the various available tests, the Boeing wedge test (BWT), used to characterize long-term durability, is presented. Efforts to accelerate the BWT involving elements of HT methodologies are discussed. Finally, a brief synopsis on the emerging role of artificial intelligence and machine learning in adhesion science is presented. The intent of this discussion is to highlight the benefits of utilizing a combinatorial approach, under the right conditions, to accelerate product development and gain a deeper understanding of adhesion-specific issues. Further, this article provides to the general practitioner the conceptual tools to develop and/or apply high-throughput workflows suitable to their situation should they be required.

Poly(acrylic acid) (PAA) are widely-used as dispersants and scale inhibitors in dish & fabric cleaning, water treatment, and oil & gas applications. After use, PAA and PAA-containing products often enter wastewater treatment systems or end up in the natural environment. Growing scrutiny on the product fate has necessitated the development of innovative, biodegradable materials. Here we report the synthesis of acrylic-acid-based copolymers that contain degradable linkages in the backbone. We exploited a stepwise "polymerization‒deprotection" pathway based on the copolymerization of 2-methylene-1,3-dioxepane (MDO) and tert-butyl acrylate (tBuA). Copolymers were prepared via free-radical polymerization followed by selective hydrolysis of the tert-butyl groups to reveal carboxylic acid functionality. MDO-AA copolymers with weight-average molecular weights (M w) of 10-20 kg/mol were prepared. Exhaustive hydrolysis of MDO-tBuA copolymers resulted in PAA oligomers with M w of 1.5‒3.0 kg/mol, suggesting relatively uniform incorporation of ring-opened MDO units in the polymer backbone. Critically, the MDO-AA copolymers showed excellent inhibition of carbonate-based scale in a laboratory titration experiment, opening the door to a new class of degradable and environmentally friendly dispersants for household cleaning and water-treatment applications.

The incorporation of hydrophobic and sparingly water-soluble monomers into emulsion polymer particles could lead to the development of new high-performance coatings, adhesives, personal care products, and other functional materials. Here, we show that the prototypical anionic surfactant sodium lauryl sulfate in combination with certain nonionic surfactants enables the incorporation of hydrophobic siloxane-containing monomers into conventional acrylic latex particles. This "mixed surfactant" method provides hydrophobic monomer loadings of up to 50 wt %, while undesirable macroscopic gel and the appearance of large particles due to microsuspension polymerization are held to <1 wt % (of total monomer). Fundamental experiments suggest that SLS and the secondary alcohol ethoxylate TERGITOL 15-S-9 surfactant increase monomer emulsion stability relative to other classes of nonionic surfactants examined. Increases in monomer emulsion droplet surface area and monomer solubilization/transport observed with this mixed surfactant system promote siloxane-containing monomer incorporation into growing latex particles. Our results and the guiding principles described here will jumpstart the development of polymerization processes for latex compositions that contain challenging or otherwise unusable sparingly soluble and water-insoluble monomers.

We report the design and characterization of thin polymer-based coatings that promote the contact transfer of DNA to soft surfaces under mild and physiologically relevant conditions. Past studies reveal polymer multilayers fabricated using linear poly(ethylene imine) (LPEI), poly(acrylic acid) (PAA), and plasmid DNA promote contact transfer of DNA to vascular tissue. Here, we demonstrate that changes in the structure of the polyamine building blocks of these materials can have substantial impacts on rates and extents of contact transfer. We used two hydrogel-based substrate models that permit identification and manipulation of parameters that influence contact transfer. We used a planar gel model to characterize films having the structure (cationic polymer/PAA/cationic polymer/plasmid DNA)x fabricated using either LPEI or one of three poly(β-amino ester)s as polyamine building blocks. The structure of the polyamine influenced subsequent contact transfer of DNA significantly; in general, films fabricated using more hydrophilic polymers promoted transfer more effectively. This planar model also permitted characterization of the stabilities of films transferred onto secondary surfaces, revealing rates of DNA release to be slower than rates of release prior to transfer. We also used a three-dimensional hole-based hydrogel model to evaluate contact transfer of DNA from the surfaces of inflatable catheter balloons used in vascular interventions and selected a rapid-transfer coating for proof-of-concept studies to characterize balloon-mediated contact transfer of DNA to peripheral arterial tissue in swine. Our results reveal robust and largely circumferential transfer of DNA to the luminal walls of peripheral arteries using inflation times as short as 15 to 30 s. The materials and approaches reported here provide new and useful tools for promoting rapid, substrate-mediated contact transfer of plasmid DNA to soft surfaces in vitro and in vivo that could prove useful in a range of fundamental and applied contexts.

Poly(acrylic acid) (PAA) is produced on an industrial scale and widely-used in applications such as personal care products and cleaning formulations that end up "down-the-drain." Relatively high molecular weight PAA is considered poorly biodegradable, but little is known about the biodegradability of low molecular weight PAA at the wastewater treatment plant according to current regulatory and industrial Organization for Economic Co-operation and Development (OECD) standards. The synthesis, separation, and characterization of a series of ultralow dispersity PAA oligomers (i.e., D < 1.10) in the molecular weight range M-n approximate to 350-1200 Da and the results of biodegradability testing are reported. Miniaturized, high-throughput screening studies in a parallel respirometer reveals a strong trend toward lower biodegradation at higher molecular weight; these results are confirmed and expanded using standardized method OECD 301F. Biodegradability reaches approximate to 40% at M-n = 380 Da, approximate to 26% at M-n = 770 Da, and approximate to 17% at M-n = 1190 Da for discrete polyacid oligomers. These data not only shed light on potential biodegradation mechanisms for linear PAA, but also may inspire the future design of biodegradable PAA-containing macromolecules.

We report an approach to waterborne and degradable latex polymers. Emulsion polymerization of vinyl acetate (VA) with the cyclic ketene acetal 2-methylene-1,3-dioxepane (MDO) yields polymer particles and latex-based coatings that are hydrolytically degradable due to the presence of backbone ester groups. Polymerization under mildly basic conditions (pH 8) and at low temperature (40 °C) is critical: if the in-process pH is too acidic or the temperature too high, MDO is lost to hydrolysis, but when the media is too alkaline, VA monomer rapidly hydrolyzes. When coated onto commercial paper, films of these degradable particle dispersions show excellent oil and grease resistance as compared to non-degradable, VA-only compositions. This new class of latex is therefore well-suited for the design of next-generation, biodegradable and compostable single-use food service products, as well as for other applications where the erosion or degradation of polymer-based films and coatings is required.

We report the design of reactive and hydrolytically degradable multilayers by the covalent layer-by-layer assembly of an azlactone-containing polymer, poly(2-vinyl-4,4-dimethylazlactone), with an acid-degradable, acetal-containing, small-molecule diamine linker. This approach yields cross-linked multilayers that contain (i) residual azlactone reactivity that can be used for further functionalization after fabrication and (ii) acid-labile cross-links that can undergo pH-triggered degradation. Thin films and hollow capsules fabricated using this approach were relatively stable in slightly basic media (pH = 7.4) but eroded and degraded gradually in mildly acidic environments (pH = 5). The residual azlactones in these materials could be functionalized by reaction with hydrophilic or hydrophobic amines to tune physicochemical properties, including surface wetting and rates of degradation/erosion. Interestingly, our results reveal that rates of degradation could be tuned over a broad range (from ∼4 h to ∼10 days) simply by post-fabrication modification of the parent reactive material. We further demonstrate the potential of acetal-containing microcapsules to be used for the acid-triggered release of encapsulated cargo. The results of in vitro experiments reveal that microcapsules loaded with fluorescently labeled dextran can be internalized by mammalian cells and that cell uptake and intracellular degradation were also influenced by the types of functional groups installed post-fabrication. The introduction of acid degradability expands the range of stimuli that can be used to trigger the destruction of these reactive materials to include changes in pH relevant to chemical and biological processes. Our results also introduce an approach to tuning degradation profiles that differs from past strategies used to design degradable multilayers. We conclude that this approach provides a new, useful, and modular platform for the design of stimuli-responsive nano/biointerfaces with transient environmental stability.

We report an approach to gas-generating polymer particles based on the acid-catalyzed thermal decomposition of poly(tert-butyl methacrylate) [p(t-BMA)] side chains to isobutene gas. The decomposition temperature of t-BMA latex is near 191 degrees C and therefore impractical for many applications. The incorporation of select acid functionalized comonomers yields a decrease to similar to 160 degrees C, as determined by thermal gravimetric analysis. This temperature can be further reduced to similar to 120 degrees C, however, via encapsulation of a thermal acid generator. This approach exploits the favorable features of emulsion polymerization processes (rapid cycle times, particle size control, high conversion, etc.) and thus provides a framework for the fabrication of high-volume tBMA-containing latex that can be used to light-weight and insulate composite materials through the creation of voids and pores. As such, gas-generating particles could reduce energy consumption needs in the transportation, construction, and other industries.

We report the influence of side chain hydrolysis on the evolution of nanoscale structure in thin films fabricated by the reactive layer-by-layer (LbL) assembly of branched poly(ethylenimine) (PEI) and poly(2-vinyl-4,4-dimethylazlactone) (PVDMA). LbL assembly of PEI and PVDMA generally leads to the linear growth of thin, smooth films. However, assembly using PVDMA containing controlled degrees of side chain hydrolysis leads to the growth of thicker films that exhibit substantial nanoscale roughness, porosity, and have resulting physicochemical behaviors (e.g., superhydrophobicity) that are similar to those of some thicker PEI/PVDMA coatings reported in past studies. Our results reveal that the degree of PVDMA partial hydrolysis (or carboxylic acid group content) influences the extent to which complex film features develop, suggesting that ion-pairing interactions between hydrolyzed side chains and amines in PEI promote the evolution of bulk and surface morphology. Additional experiments demonstrate that these features likely arise from polymer/polymer interactions at the surfaces of the films during assembly, and not from the formation and deposition of solution-phase polymer aggregates. When combined, our results suggest that nanoporous structures and rough features observed in past studies likely arise, at least in part, from some degree of adventitious side chain hydrolysis in the PVDMA used for film fabrication. Our results provide useful insight into molecular-level features that govern the growth and structures of these reactive materials, and provide a framework to promote nanoscale morphology reliably and reproducibly. The principles and tools reported here should prove useful for further tuning the porosities and tailoring the physicochemical behaviors of these reactive coatings in ways that are important in applied contexts.

The radical polymerization of methyl methacrylate (MMA) by the thermal initiator tert-butyl peroxypivalate (tBPPiv) and in the presence of various thiol-containing chain transfer agents (CTAs) has been studied to quantitatively determine the chemical selectivity and fate of initiator radicals. Deuterated MMA-d(5) was used to follow polymerization reactions by 1D and 2D NMR spectroscopy and to determine the identity and quantity of small molecule byproducts, together with the distribution of polymer end-groups. These data have resulted in a detailed understanding of initiator decay pathways, radical selectivity, and of key importance to the design of well-defined polymers for commercial applications, the efficiency of so-called end-group functionalization. In the presence of a thiol-containing small molecule, chain transfer to CTA leads predominantly to initiation by the resulting thiyl radical; however, direct initiation by initiator radicals and a variety of other reactions reduce the total number of CTA-functionalized chain-ends. The approach reported here gives fundamental insights into the fates of radicals in the polymerization of a model methacrylate, increased control over end-groups, and can be extended to a range of commercially relevant polymer compositions. Moreover, these results provide a quantitative framework that can potentially open the door to the design of end-functional polymers by industrially relevant methods, avoiding the need for more time-consuming and complex reversible-deactivation radical polymerization (RDRP) techniques.

We report the aqueous lyotropic mesophase behaviors of protonated amine-based "lipidoids," a class of synthetic lipid-like molecules that mirrors essential structural features of the multitail bacterial amphiphile lipid A. Small-angle X-ray scattering (SAXS) studies demonstrate that the protonation of the tetra(amine) headgroups of six-tail lipidoids in aqueous HCl, HNO3, H2SO4, and H3PO4 solutions variably drives their self-assembly into lamellar (Lα) and inverse micellar (III) lyotropic liquid crystals (LLCs), depending on acid identity and concentration, amphiphile tail length, and temperature. Lipidoid assemblies formed in H2SO4(aq) exhibit rare inverse body-centered cubic (BCC) and inverse face-centered cubic (FCC) micellar morphologies, the latter of which unexpectedly coexists with zero mean curvature Lα phases. Complementary atomistic molecular dynamics (MD) simulations furnish detailed insights into this unusual self-assembly behavior. The unique aqueous lyotropic mesophase behaviors of ammonium lipidoids originate in their dichotomous ability to adopt both inverse conical and chain-extended molecular conformations depending on the number of counterions and their identity, which lead to coexisting supramolecular assemblies with remarkably different mean interfacial curvatures.

We report the design and synthesis of a class of hybrid latex particle that combines the elastomeric properties of polyolefins with the physicochemical diversity of acrylics. These hybrid polyolefin-acrylic particles are obtained in two steps, starting from the mechanical dispersion of a polyolefin resin to yield a colloidally stable particle dispersion, which is then used in a second step as a seed for the free radical emulsion polymerization of an acrylic phase. Imaging of the resulting particles by scanning electron and atomic force microscopy reveals a distinct lobed morphology, where acrylic polymer is associated with the surface of the polyolefin dispersion. Using gel permeation chromatography (GPC), we quantify the degree of grafting between the core and the acrylic phase, while analysis by dynamic mechanical analysis (DMA) shows that key properties of the polyolefin remain unaffected by the emulsion polymerization process. Process changes including varying the polyolefin/acrylic ratio, monomer addition method, initiator type, and acrylic composition can be used to control the surface coverage and size of the acrylic lobes, and therefore tune the particle morphology. This approach is modular both in terms of the polyolefin materials and additives that can be used to fabricate the core, as well as the physicochemical properties of the acrylic phase (composition, glass transition temperature, chemical functionality, etc.) and provides opportunities to design hybrid particles for a range of advanced applications.

Bacillus thuringiensis (Bt) is one of the most widely used microbial pesticides and currently represents the largest share of the biopesticide market (~67%). Bt is highly active against insects such as caterpillars, mosquito larvae, and blackflies that transfer river blindness in Africa. During the sporulation of Bt, crystal aggregates of proteins are produced, which along with its spores, are responsible for its high insecticidal activity. However, Bt lacks long-term activity in the field due to the UV sensitivity of the spores and lack of persistence of crystal proteins on plant leaves due to rain. In this study, we present the development of materials providing rainfastness and UV resistance that perform above benchmarks for both the liquid and dry flowable Bt formulations currently available. The high rainfastness observed was maintained after spray drying of liquid Bt formulations containing our rainfastness agents and redispersion in water of the dry products obtained. Finally, we present the performance of different OMRI-certified rainfastness agents.

We report the synthesis and characterization of catechol-functionalized film-forming latexes that display excellent adhesion to low-surface-energy polyolefin-based substrates. The aromatic 1,2-diol functional group in catechol derivatives is believed to be responsible for enhancing the adhesion of a variety of polymers to a range of substrates. Here, we describe a postpolymerization modification approach to the design of emulsion polymers with catechol-functionalized side chains. A series of analogous small-molecule reactions, together with latex characterization by infrared (IR) spectroscopy and liquid chromatography (LC) methods, provides evidence for polymer functionalization. Films prepared from catechol-containing latexes displayed remarkable adhesion to challenging, commercially-available thermoplastic polyolefin (TPO) (as determined by a standard ASTM cross-hatch method). We provide evidence that covalent bonding and the unique catechol structure are required to promote adhesion. The catechol-functionalized emulsion polymers reported here represent a new class of functional latex, and this postpolymerization modification approach will present further opportunities to improve, modulate, and control the adhesion of water-borne coatings to a variety of polyolefin-based substrates.