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Abstract In this study, poly(ethylene terephthalate)‐block‐polyethylene (PET‐PE) multiblock copolymers (MBCPs) with block molar masses of ~4 or 7 kg mol⁻¹and either alternating or random block sequencing, and a PE‐PET‐PE triblock copolymer (TBCP) of comparable total molar mass, were synthesized. To explore the effect of molecular architecture on compatibilization, both MBCPs and TBCPs were blended into 80/20 wt/wt mixtures of PET/linear low‐density PE (LLDPE). Compatibilization was remarkably efficient for all MBCP types, with the addition of 0.2 wt% yielding blends nearly as tough as PET homopolymer. Addition of MBCP also significantly decreases LLDPE dispersed phase sizes compared to PET/LLDPE neat blends, as much as 80% in as‐mixed blends and by a factor of 10 in post‐mixing thermally annealed samples. Conversely, the TBCP was less efficient at decreasing domain sizes of the blends and improving the mechanical properties, requiring loadings of 1 wt% to produce comparably tough blends. Peel tests of PET/BCP/LLDPE trilayer films showed that both MBCPs and TBCP all improve interfacial strength over a PET‐PE bilayer film by two orders of magnitude; however, when the BCPs were preloaded into LLDPE, only the MBCP containing films showed strong adhesion highlighting their potential utility as adhesive agents in multilayer films. 

Abstract Poly(lactic acid) (PLA) is a commercially available bio‐based polymer that is a potential alternative to many commodity petrochemical‐based polymers. However, PLA's thermomechanical properties limit its use in many applications. Incorporating polymer‐grafted cellulose nanocrystals (CNCs) is one potential route to improving these mechanical properties. One key challenge in using these polymer‐grafted nanoparticles is to understand which variables associated with polymer grafting are most important for improving composite properties. In this work, poly(ethylene glycol)‐grafted CNCs are used to study the effects of polymer grafting density and molecular weight on the properties of PLA composites. All CNC nanofillers are found to reinforce PLA above the glass transition temperature, but non‐grafted CNCs and CNCs grafted with short PEG chains (<2 kg mol⁻¹) are found to cause significant embrittlement, generally resulting in less than 3% elongation‐at‐break. By grafting higher molecular weight PEG (10 kg mol⁻¹) onto the CNCs at a grafting density where the polymer chains are predicted to be in the semi‐dilute polymer brush conformation (~0.1 chains nm⁻²), embrittlement can be avoided. 

Abstract Extensional flow properties of polymer solutions in volatile solvents govern many industrially-relevant coating processes, but existing instrumentation lacks the environment necessary to control evaporation. To mitigate evaporation during dripping-onto-substrate (DoS) extensional rheology measurements, we developed a chamber to enclose the sample in an environment saturated with solvent vapor. We validated the evaporation-controlled DoS device by measuring a model high molecular weight polyethylene oxide (PEO) in various organic solvents both inside and outside of the chamber. Evaporation substantially increased the extensional relaxation time$$\lambda _{E}$$ ${\lambda }_E$for PEO in volatile solvents like dichloromethane and chloroform. PEO/chloroform solutions displayed an over 20-fold increase in$$\lambda _{E}$$ ${\lambda }_E$due to the formation of an evaporation-induced surface film; evaporation studies confirmed surface features and skin formation reminiscent of buckling instabilities commonly observed in drying polymer solutions. Finally, the relaxation times of semi-dilute PEO/chloroform solutions were measured with environmental control, where$$\lambda _{E}$$ ${\lambda }_E$scaled with concentration by the exponent$$m=0.62$$ $m=0.62$. These measurements validate the evaporation-controlled DoS environment, and confirm that chloroform is a good solvent for PEO, with a Flory exponent of$$\nu =0.54$$ $\nu =0.54$. Our results are the first to control evaporation during DoS extensional rheology, and provide guidelines establishing when environmental control is necessary to obtain accurate rheological parameters. 

Cellulose nanocrystal (CNC)-reinforced composites are gaining commercial attention on account of their high strength and sustainable sourcing. Grafting polymers to the CNCs in these composites has the potential to improve their properties, but current solution-based synthesis methods limit their production at scale. Utilizing dynamic hindered urea chemistry, a new method for the melt-functionalization of cellulose nanocrystals has been developed. This method does not require toxic solvents during the grafting step and can achieve grafting densities competitive with state-of-the-art solution-based grafting methods. Using cotton-sourced, TEMPO-oxidized CNCs, multiple molecular weights of poly(ethylene glycol) (PEG) as well as dodecane, polycaprolactone, and poly(butyl acrylate) were grafted to the CNC surface. With PEG-grafted nanoparticles, grafting densities of 0.47 chains nm−2 and 0.10 chains nm−2 were achieved with 2000 and 10,000 g mol−1 polymer chains respectively, both of which represent significant improvements over previous reports for solution-based PEG grafting onto CNCs. 

Materials made from covalently cross-linked polymer networks are ubiquitous in everyday life but are difficult to process at the end of their life cycle. Therefore, it is essential to design materials with sustainability in mind to reduce the detrimental effects of plastic waste buildup. Functionalized triazines such as 1,3,5-triazine-2,4,6-triamine (melamine), hexamethylolmelamine (HMM), and hexakis(methoxymethyl)melamine (HMMM) are key components of robust thermosets, adhesives, and coatings. We combine HMM and HMMM with an alkoxysilane to produce transparent thermosets with remarkable glass adhesion. The dynamicity of silyl ether bonds in the network makes the materials susceptible to methanolysis, enabling the recovery of HMMM and the substrate. A combination of solution- and solid-phase techniques is used to elucidate both gelation and degradation pathways. 

Carbamate formation and exchange catalysts enable efficient polyurethane (PU) manufacturing, as well as emerging recycling and reprocessing methods for PU thermosets. Zirconium β-diketonate complexes, such as Zr acetylacetonate [Zr(acac)4], are effective alternatives to toxic organotin catalysts that have been used for PU reprocessing. Here, we report that Zr(acac)4 undergoes a thermally activated process in the PU network during reprocessing that transforms it into a more active carbamate exchange catalyst. This process is associated with the irreversible loss of acetylacetonate ligands and is not observed for the more sterically hindered Zr 2,2,6,6-tetramethyl-3,5-heptanedione [Zr(tmhd)4] complex. Crossover experiments between PU thermoplastics indicated enhanced carbamate exchange after the thermal activation of Zr(acac)4 in the presence of one of the PUs, whereas a sample of Zr(acac)4 activated in the absence of the PU had no catalytic activity. Thermal gravimetric analysis suggested that this process is associated with the loss of one protonated acac ligand. Stress relaxation analysis of PU thermosets indicated a distinct change in the characteristic relaxation time associated with the thermal activation of Zr(acac)4 at temperatures above 140 °C; no such change was observed for samples reprocessed using Zr(tmhd)4. Density functional theory and molecular experiments suggest that irreversible ligand exchange of acac with alkoxide or carbamate reduces the activation energy for urethane formation and reversion. Furthermore, the Zr(acac)4 catalyst activated in the presence of a PU’s polyol precursor provided more porous and less dense PU foams compared to those made using the unactivated Zr(acac)4 catalyst. These findings are important for developing improved PU synthesis and recycling processes. Thermally activating a catalyst during reprocessing may provide more nuanced control of the in-use and reprocessing characteristics of PU thermosets. 

There is a growing concern that nanoplastic pollution may pose planetary threats to human and ecosystem health. However, a quantitative and mechanistic understanding of nanoplastic release via nanoscale mechanical degradation of bulk plastics and its interplay with photoweathering remains elusive. We developed a lateral force microscope (LFM)-based nanoscratch method to investigate mechanisms of nanoscale abrasive wear of low-density polyethylene (LDPE) surfaces by a single sand particle (simulated by a 300 nm tip) under environmentally relevant load, sliding motion, and sand size. For virgin LDPE, we found plowing as the dominant wear mechanism (i.e., deformed material pushed around the perimeter of scratch). After UVA-weathering, the wear mechanism of LDPE distinctively shifted to cutting wear (i.e., deformed material detached and pushed to the end of scratch). The shift in the mechanism was quantitatively described by a new parameter, which can be incorporated into calculating the NP release rate. We determined a 10-fold higher wear rate due to UV weathering. We also observed an unexpected resistance to initiate wear for UV-aged LDPE, likely due to nanohardness increase induced by UV. For the first time, we report 0.4–4 × 10–3 μm3/μm sliding distance/μN applied load as an initial approximate nanoplastic release rate for LDPE. Our novel findings reveal nanoplastic release mechanisms in the environment, enabling physics-based prediction of the global environmental inventory of nanoplastics. 

Thermoset networks are chemically cross-linked materials that exhibit high heat resistance and mechanical strength; however, the permanently cross-linked system makes end-of-life degradation difficult. Thermosets that are inherently degradable and made from renewably derived starting materials are an underexplored area in sustainable polymer chemistry. Here, we report the synthesis of novel sugar- and terpene-based monomers as the enes in thiol–ene network formation. The resulting networks showed varied mechanical properties depending on the thiol used during cross-linking, ranging from strain-at-breaks of 12 to 200%. Networks with carveol or an isosorbide-based thiol incorporated showed plastic deformation under tensile stress testing, while geraniol-containing networks demonstrated linear stress–strain behavior. The storage modulus at the rubbery plateau was highly dependent on the thiol cross-linker, showing an order of magnitude difference between commercial PETMP, DTT, and synthesized Iso2MC. Thermal degradation temperatures were low for the networks, primarily below 200 °C, and the Tg values ranged from −17 to 31 °C. Networks were rapidly degraded under basic conditions, showing complete degradation after 2 days for nearly all synthesized thermosets. This library demonstrates the range of thermal and mechanical properties that can be targeted using monomers from sugars and terpenes and expands the field of renewably derived and degradable thermoset network materials. 

An H-polymer has an architecture that consists of four branches symmetrically attached to the ends of a polymer backbone, similar in shape to the letter “H”. Here, a renewable H-polymer efficiently synthesized using only ring-opening transesterification is demonstrated. The strategy relies on a tetrafunctional poly(±-lactide) macroinitiator, from which four poly(±-lactide) branches are grown simultaneously. 1H NMR spectroscopy, size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization (MALDI) spectrometry were used to verify the macroinitiator purity. Branch growth was probed using 1H NMR spectroscopy and SEC to reveal unique transesterification phenomena that can be controlled to yield architecturally pure or more complex materials. H-shaped PLA was prepared at the multigram scale with a weight-average molar mass Mw > 100 kg/mol and low dispersity Đ < 1.15. Purification involved routine precipitations steps, which yielded products that were architecturally relatively pure (∼93%). Small-amplitude oscillatory shear and extensional rheology measurements demonstrate the unique viscoelastic behavior associated with the H-shaped architecture. 

Semicrystalline poly(l-lactide) (PLLA) is a leading biosourced, compostable alternative to conventional plastics but lacks sufficient toughness for many applications. Chain alignment via uniaxial stretching may be used to toughen PLLA but often creates anisotropic materials that are tough in the machine direction (MD) but brittle in the transverse direction (TD). This work reports uniaxially stretched films of PLLA blended with 3 wt % poly(ethylene oxide)-block-poly(butylene oxide) (PEO-PBO), which exhibit as much as a 5-fold increase in toughness in the TD compared to similarly stretched neat PLLA films─and elucidates the impact of PEO–PBO particles on the relationship between stretching, crystallization behavior, and resultant mechanical properties. Faster stretching rates were correlated with higher yield stress and a greater degree of crystallite alignment in the PEO–PBO/PLLA blends. This trend highlights the synergistic relationship between crystallinity and chain alignment and suggests a competing mechanism of heterogeneous crystallite nucleation around PEO–PBO particles. Importantly, PEO–PBO/PLLA exhibited a TD elongation at break of 36%, five times greater than the value of similarly stretched neat PLLA and even greater than the corresponding MD value of either material. Taken together, these findings demonstrate that uniaxial stretching of PEO–PBO/PLLA blends produces biaxially tough films, with the fastest stretching conditions producing the greatest enhancement in TD toughness.