ACS Macro Letters最新文献

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 (T_g). We previously showed that addition of a poly(ethylene-oxide)-block-poly(butylene oxide) diblock copolymer (PEO–PBO) forms macrophase-separated rubbery domains in PLA that can impart significant toughness at only 5 wt %. This work demonstrates that PEO–PBO/PLA blends exhibit substantial toughness for at least nine months, beyond the average lifetime of single-use packaging, even amidst oxidative degradation of PEO–PBO into oligomeric products. Due to the glassy nature of the PLA matrix, these degradation products are confined to macrophase-separated domains, and the blend morphology is preserved. However, modest thermal annealing (∼60 °C) causes these domains to rapidly reduce in area fraction and size from migration and solubilization of the PEO–PBO degradation products into PLA, which plasticizes PLA and reduces the blend T_g. As a result, aged PEO–PBO/PLA blends degrade in just under half the time of similarly aged neat PLA when submerged in artificial seawater at 50 °C. This surprising combination of properties addresses two of PLA’s most significant limitations with a single additive by (1) toughening the PLA during its useful lifetime and then (2) accelerating its degradation rate by heat-triggered plasticization when exposed to elevated temperatures at end-of-life, such as those of industrial (or even home) compost.

Ion-containing polymers are subject to a wide range of hydration conditions across electrochemical and water treatment applications. Significant work on dry polymer electrolytes for batteries and highly swollen membranes for water purification has informed our understanding of ion transport under extreme conditions. However, knowledge of intermediate conditions (i.e., low hydration) is essential to emerging applications (e.g., electrolyzers, fuel cells, and lithium extraction). Ion transport under low levels of hydration is distinct from the extreme conditions typically investigated, and the relevant physics cannot be extrapolated from existing knowledge, stifling materials design. In this study, we conducted ion transport measurements in LiTFSI-doped polyethers that were systematically hydrated from dry conditions. A semiautomated apparatus that performs parallel measurements of water uptake and ionic conductivity in thin-film polymers under controlled humidity was developed. For the materials and swelling range considered in this study (i.e., <0.07 g water/g dry polymer electrolyte), ionic conductivity depends nonlinearly on water uptake, with the initial sorbed water weakly affecting conductivity. With additional increases in swelling, more significant increases in conductivity were observed. Remarkably, changes in conductivity induced by water sorption were correlated with the number of water molecules per lithium ion, with the normalized molar conductivity of different samples effectively collapsing onto one another until this unit of hydration exceeded the solvation number of lithium ions under aqueous conditions. These results provide important knowledge regarding the effects of trace water contamination on conductivity measurements in polymer electrolytes and demonstrate that the lithium-ion solvation number marks a key transition point regarding the influence of water on ion transport in ion-containing polymers.

In this study, segmented hyperbranched copolymers with degradable and chain extendable cross-linker branch points were synthesized via green light-activated photoiniferter copolymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and a trithiocarbonate-derived dimethacrylate. A series of segmented hyperbranched copolymers with different degrees of branching were synthesized by changing the feed ratio of PEGMA to cross-linker to chain transfer agent. The segmented hyperbranched copolymers could be degraded into linear polymer chains by removing the trithocarbonate groups, which provides fundamental insights into the growth of primary chains during photoiniferter copolymerization. Switching to blue light irradiation allowed for the chain extension of poly(N,N-dimethylacrylamide) (PDMA) both at the branch points and at the chain ends. Finally, the formed segmented hyperbranched copolymers were explored as macromolecular chain transfer agents to prepare segmented hyperbranched block copolymer nanoparticles via polymerization-induced self-assembly. This study not only leads to new examples of degradable and chain extendable segmented hyperbranched polymers but also provides important insights into the formation of branched polymers via copolymerization of multivinyl monomers.

Polyhydroxyalkanoates (PHAs) have served as promising alternatives to traditional petroleum-based plastics. Chemical synthesis of stereoregular PHAs via stereocontrolled ring-opening polymerization (ROP) of racemic β-lactones was a desired strategy with a formidable challenge. Herein, we developed a class of DiMeBiPh-salen yttrium complexes that adopted a cis-α configuration for stereoselective ROP of rac-β-butyrolactones (rac-BBL) and rac-β-valerolactone (rac-BVL). Notably, catalyst Y5 promoted robust polymerization with TOF up to 10⁴ h^–1 and furnished syndiotactic P3HB, P3HV, and P(3HB)-co-P(3HV) copolymers with P_r values of up to 0.95. Varying the compositions in P(3HB)-co-P(3HV) copolymers offered an intriguing opportunity to fine tune the thermal properties. Our kinetic study supported a polymeryl exchange mechanism. This work demonstrated that the DiMeBiPh-salen system could serve as a new catalytic framework for the stereoselective ROP of β-lactones, which leverages the catalyst design for stereoselective polymerization.

The construction of single-component, white-light-emitting, conjugated polymers always utilizes fluorescence resonance energy transfer (FRET) for efficient emission. However, the main challenges in developing such materials primarily come from the effects of aggregation states during solution processing and the precise structural control required for the synthesis of compounds. Both aspects can affect the FRET between different lumophores in white-light-emitting materials. A novel supermolecular assembly strategy using new conjugated polymers (CPs) to fabricate single-component white-light-emitting CPs nanobowls (CPNBs) was developed to overcome the two difficulties. Specifically, through molecular structure engineering, side chains have been modified with a uracil group capable of hydrogen bonding, which stabilized the nanobowl structure during the supramolecular assembly process. Furthermore, by blending two kinds of CPs emitting different colors during the supramolecular assembly, single-component, white-light-emitting CPNBs have been achieved. The supramolecular strategy has resulted in stable and high-brightness, white-light emission, whether in aqueous solutions of different concentrations or in solid-state, polymer-based, composite materials. It also offers a more straightforward and environmentally friendly synthesis process for white-light-emitting organic materials.