Macromolecules最新文献

Epoxycyclohexyl- and dodecyl-bearing ladder-like polysilsesquioxanes (EDLASQs) are synthesized through the hydrolysis of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (ECTMS) and dodecyltrimethoxysilane (DTMS) and co-condensation of their hydrolysates. Such copolymerization reactions are traditionally conducted in tetrahydrofuran and water containing K₂CO₃ as the catalyst. The differing water compatibilities of the two monomers cause their reaction rates to differ drastically, making their random copolymerization questionable. In this work, we demonstrate that the reaction rates of the more hydrophobic DTMS monomer can be increased by adding a surfactant, either sodium dodecyl sulfate or cetyltrimethylammonium bromide, which increases the dispersion of the aqueous phase in monomers and the area of the monomer/water interfaces. Due to the homogenized hydrolysis rates of ECTMS and DTMS, the EDLASQ prepared in the presence of a surfactant possesses E/D molar ratios close to the ECTMS-to-DTMS feed molar ratio even at the early stages of their copolymerization. In contrast, EDLASQ prepared without a surfactant is enriched with E at earlier polymerization times, suggesting the blocky nature of the produced copolymers. Coating samples of an EDLASQ at an E/D molar ratio of 8/1 prepared using the new method exhibit high light transmission (99.9% at 600 nm after substrate absorption correction), high hardness (1.26 GPa), and enhanced water repellency. The proposed method is general and should be useful for the synthesis of other random co-LASQs.

Thanks to their excellent thermomechanical properties, cross-linked polymers are widely used for a myriad of applications. However, due to the presence of covalent cross-links, these polymers are usually considered nonrecyclable. For hydrocarbon polymers, this problem is particularly acute because, due to the lack of functional groups, the few known cross-linking strategies are based on highly stable covalent bonds. To address this problem, we propose here a strategy to physically cross-link a polymer by adding a supramolecular host, which can complex two pendant alkyl groups of a macromolecular chain. We demonstrate that dimethoxypillar[5]arene (DM-P[5]A) possesses this unique ability. Taking advantage of this phenomenon, poly(1-decene) (PD) is conveniently cross-linked upon the addition of DM-P[5]A, thus transforming a viscous liquid into an elastomer. Furthermore, reversible cross-linking is also efficient in the solid state: for example, high-T_g poly(5-hexyl-2-norbornene) (PNBE) becomes cross-linked when containing DM-P[5]A, resulting in polymers with greater mechanical properties. Remarkably, DM-P[5]A can be simply washed out with a suitable solvent, allowing the recovery of the pristine polymer free of cross-links. This very straightforward strategy thus allows any polymer containing pendant alkyl groups to be reversibly cross-linked, thus essentially solving the problem of recyclability of cross-linked polymers.

We undertook a detailed rheological investigation to evaluate the kinetic parameters of the forward and reverse Diels–Alder (DA) reactions of a model network cross-linked using a furan prepolymer and a common aromatic bismaleimide. At high temperature where the Winter–Chambon’s criterion of frequency-independence was more applicable, a multiwave technique permitted van’t Hoff analysis and calculation of the reaction thermodynamic parameters, specifically the enthalpy and entropy of the reaction: ΔH° = −38.3 ± 5.2 kJ mol^–1 and ΔS° = −94.3 ± 13.4 J mol^–1. At mild temperatures where the G′–G″ crossover point is experimentally convenient to measure gelation, isothermal tests were used to obtain reasonable fDA kinetic parameters from Eyring analysis such as the apparent activation enthalpy and entropy of $\Delta H_{\mathrm{fDA}}^{‡}=76.8\pm 6.9{\mathrm{kJ}\mathrm{mol}}^{-1}$ and $\Delta S_{\mathrm{fDA}}^{‡}=-82.8\pm 22.2J{\mathrm{mol}}^{-1}{K}^{-1}$. Comparable rheokinetic methods include cross-linking density measurements and stress relaxation tests to calculate effective kinetics, whereas the critical gel conversion was consistently applied here. Rate data are fitted with the Arrhenius equation for comparison purposes and the Eyring equation to demonstrate its broader utility.

Inspired by natural enzymes, synergy is widely utilized in small molecule recognition and transformation, but has not been fully explored in polymer synthesis. Herein, we present an enzyme-mimicking catalyst design strategy for constructing rigid-flexible binuclear catalysts (RFBCs), aiming to boost the copolymerization of CO₂ and propylene oxide (PO). The key design strategy of RFBCs is to boost intramolecular synergy by spatial proximity of active sites imposed by rigid skeleton, while a flexible linker affords dynamic interactions of active centers. The optimal catalyst Nap-Al₂, featured with rigid naphthalene skeleton grafting two adjacent aluminum porphyrins through soft alkyl chains, exhibits outstanding catalytic performance (5000 h^–1) outperforming the previously reported polymeric catalysts (3100 h^–1) under similar conditions. Moreover, Nap-Al₂ exhibits great thermal stability at high temperatures up to 140 °C. A comprehensive catalytic cycle based on dynamic synergy has been proposed, taking into account the key intermediates involved in the copolymerization of CO₂/PO. Overall, we present that the construction of RFBCs for designing enzyme-mimicking catalysts is not only suitable for the ROCOP of CO₂/PO but also conducive to future investigation for related polymerization processes, such as the ring-opening of lactones.

Phosphine ligands are widely used for transition metal compounds that catalyze various reactions. The present paper reports the coupling polymerization of optically active bidentate phosphine ligands, PPh₂–R–PPh₂ (R: spacer containing amino acid moieties) with PtCl₂L₂ (L: 1,5-cyclooctadiene, benzonitrile). The selectivity of trans-/cis-geometries, formation of polymers (−[−PPh₂–R–PPh₂–PtCl₂−]_n−) vs cyclic compounds depending on polymerization conditions, as well as chiroptical properties and hydrosilylation catalysis of the polymers were studied.

One-dimensional ultrathin organic nanotubes (UTONTs) are of favorable potential as absorbents due to their hollow nanostructures, high-aspect-ratio, large specific surface area, and tailorable functions. However, the development of polymer-based and stimuli-responsive UTONTs for highly efficient and controllable removal of pollutants remains challenging. Herein, we report the self-assembly of side-chain amphiphilic alternating azocopolymers to generate cationic and photoresponsive ultrathin polymer nanotubes (UTPNTs) with an average diameter of ∼548 nm and a tubular wall thickness of ∼2.8 nm. Owing to the photoisomerization of azobenzene units, a reversible transformation from the UTPNTs to ultrathin polymer vesicles (UTPVs, a vesicular thickness of 2.4 nm, a diameter of 115 nm) was achieved upon alterative irradiation with UV and visible light, proving the attractive photoresponsive feature. The proof-of-concept adsorption performance for both UTPNTs and UTPVs was evaluated toward the anionic dye Congo red, with a photocontrollable and highly efficient adsorption activity that was highly dependent on ultrathin hollow structures and electrostatic interactions. The as-prepared UTPNTs exhibited favorable adsorption capacity, with a large adsorption amount of 1248.3 mg·g^–1 and a short equilibrium time of ∼6 min, greater than that of UTPVs (638.2 mg·g^–1). Our work provides a simple strategy for generating stimuli-responsive UTONTs with desirable adsorption performance.

Chain shuttling polymerization is a powerful approach for efficiently producing olefin block copolymers via simple one-pot polymerization. Herein, this method was used to synthesize ethylene-norbornene cycloolefin block copolymers (COBCs). Two bis(salicylaldiminato)titanium complexes with different monomer selectivities were used to generate alternating hard and soft blocks of high and low norbornene incorporation, respectively, in the presence of chain shuttling agents (diethyl zinc). The high glass transition temperature (T_g) of the hard blocks contributed to their high tensile strength, while the low T_g of the soft blocks led to their high ductility. By varying the concentration of norbornene during the copolymerization process, it is possible to tune the T_g values of the hard and soft blocks, thus achieving a transition in the mechanical properties of the COBCs from typical elastomers to plastics while maintaining high ductility and transparency. Compared with random cycloolefin copolymer plastics, the COBC in this study exhibited a 55-fold increase in elongation at break and maintained comparable tensile strength. This study highlights the development of a new class of chain shuttling catalytic systems to produce COBCs with widely tunable T_g values to modulate their mechanical properties.

The immense dependence of the glass transition temperature T_g on molecular weight M is one of the most fundamentally and practically important features of polymer glass formation. Here, we report on molecular dynamics simulations of three model linear polymers of substantially different complexity demonstrating that the 70-year-old canonical explanation of this dependence (a simple chain end dilution effect) is likely incorrect at leading order. Our data show that end effects are present only in relatively stiff polymers and, furthermore, that the magnitude of these end effects diminish on cooling. We find that T_g(M) trends are instead dominated by shifts in T_g throughout the entire polymer chain rather than through a chain end effect. We show that these data can be rationalized via a generic two-barrier model of T_g and its M-dependence, motivated by the Elastically Collective Nonlinear Langevin Equation theory. More broadly, this work indicates need to reopen the question of the origin of the T_g(M) dependence in linear polymers (and macromolecules at large), as well as an opportunity to reveal new glass formation physics with renewed study of M effects on T_g.

Mechanochromic polymeric materials have enormous potential applications in stress-sensing and damage detection. These types of polymers including poly(methyl acrylate), poly(methyl methacrylate), poly(urethane), and poly(ε-caprolactone) have been achieved through various methods, such as postfunctional reaction, free radical polymerization, polycondensation, and ring-opening polymerization. However, coordination polymerization to incorporate mechanochromophores into semicrystalline polyethylene, an extremely important and common plastic, is rare. Herein, we report functionalized polyethylene materials via coordination copolymerization of ethylene and a well-designed comonomer C4-ABF containing the mechanochromic group catalyzed by phosphine–sulfonate palladium catalysts and the following cross-linking reaction. These copolymer materials exhibit a visible color change under force stimulus, transferring the force signal to the color signal. The red–green–blue (RGB) color analysis method is adapted to investigate the relationship between stress–strain and color change. It is noted that the blue channel intensity has a positive correlation with Hencky stress.

Synthesis of copolymers using 2,5-furandicarboxylic acid (FDCA) and isosorbide (IS) as renewable feedstocks remains a challenge in conventional melt polycondensation. Herein, acyclic diene metathesis (ADMET) polymerization of several kinds of α,ω-dienes containing an FDCA or IS moiety was performed under mild conditions to afford biobased polyesters with an unsaturated chain structure and tunable glass transition temperature between −40 and 34 °C. Meanwhile, FDCA-derived α,ω-diene was used as a comonomer to undergo inverse vulcanization with elemental sulfur, affording a polysulfide as the cross-linking agent suitable for modifying ADMET polyesters. The cross-linked polyesters showed improved mechanical properties and good reprocessability. Furthermore, the modified polyester composites exhibited excellent anti-ultraviolet (UV) performance with a high UV protection factor of 251 and maintained almost the original mechanical properties even after 72 h of UV light exposure. This work provided a practical approach for the high-value-added utilization of ADMET polyesters as sustainable functional materials.