Macromolecules最新文献

Traditional π-conjugated luminescent macromolecules typically suffer from aggregation-caused quenching (ACQ) and high cytotoxicity, and they require complex synthetic processes. In contrast, nonconventional luminescent macromolecules (NCLMs) with nonconjugated structures possess excellent biocompatibility, ease of preparation, unique luminescence behavior, and emerging applications in optoelectronics, biology, and medicine. NCLMs are currently believed to produce inherent luminescence due to through-space conjugation of overlapping electron orbitals in solid/aggregate states. However, as experimental facts continue to exceed expectations or even overturn some previous assumptions, there is still controversy about the detailed luminous mechanism of NCLMs, and extensive studies are needed to further explore the mechanism. This Perspective highlights recent progress in NCLMs and classifies and summarizes these advances from the viewpoint of molecular design, mechanism exploration, applications, and challenges and prospects. The aim is to provide guidance and inspiration for the huge fundamental and practical potential of NCLMs.

Microinjection-molding subjects the polymer melt to high cooling and shear rates, which significantly affects the crystallization behavior during solidification. In this work, fast scanning chip calorimetry, conventional differential scanning calorimetry, melt rheology experiments, and polarized light optical microscopy permitted drawing conclusions about the crystallization of polyoxymethylene under such processing conditions. Computer simulations and Cox–Merz experiments predict orientation of molecular segments and shear-induced formation of crystal nuclei in all regions of the component, that is, in both the skin and core. However, as the result of the interplay between the cooling rate/crystallization temperature and the chain relaxation time, the survival of nuclei is restricted to skin-near layers. In contrast to the fast cooling skin, in the slowly cooling core region, the initially oriented structure recovers to the random coil state due to the much shorter relaxation time compared to the crystallization time. The study suggests that structure formation of crystallizable polymers during melt processing, including microinjection molding, largely depends on the (temperature-dependent) ratio between the chain relaxation and chain crystallization time.

Polymer vitrimers are a new class of materials that combine the advantages of thermoplastics and thermosets. This is due to the dynamic nature of the chemical bonds linking different chains. However, how this property affects the polymer dynamics at different length scales is still an open question. Here, we investigate the dynamics of model vitrimers based on well-defined polyisoprene (PI) chains using broadband dielectric spectroscopy. In this way, we study the polymer dynamics from the segmental to the whole chain scale, taking advantage of the fact that PI belongs to the class of molecules that exhibit a net dipole moment associated with the end-to-end vector. Three distinct relaxation phenomena are identified. The fastest relaxation is attributed to the segmental PI dynamics with a small influence of the cross-linking. An intermediate relaxation attributed to the dipolar character of the cross-linker is also observed. The slower identified relaxation component, corresponding to limited fluctuations of the end-to-end PI chains, is found to be determined by the dynamics of the clusters formed by the cross-linkers with an average time scale orders of magnitude faster than that of the terminal relaxation as inferred from the viscous flow.

A strong memory effect has been identified in copolymers even above the equilibrium melting temperature, which accelerates the subsequent recrystallization process. In this study, two series of novel 1-butene-based random copolymers were synthesized from two comonomers: 4-phenyl-1-butene (PhB) and 4-anthryl-1-butene (AnB). PhB and AnB introduced phenyl and anthryl groups, respectively, into the poly(1-butene) main chain. The occurrence and evolution of the memory effect were systematically explored in the presence of these designed counits via differential scanning calorimetry. The strong memory effect above the equilibrium melting temperature occurred in both copolymers, while their critical compositions of incorporation varied largely. The memory effect was triggered with the incorporated PhB counits up to 5.33 mol % for a fixed annealing period of 10 min. However, the incorporation of only 0.6 mol % of the sterically hindered large AnB counits induced a strong memory effect. A plot of the crystallization temperature as a function of the melt temperature (T_melt) showed a counterintuitive bell-shaped trend for AnB copolymers. The strength of the memory effect increased on extending the holding duration, contrary to the customary decaying behavior. Such a developed memory effect clearly explains the origin of the observed inversion of the crystallization rate over a broad temperature range.

Insufficient charge separation and sluggish exciton transport seriously restrict the practical application of photocatalytic uranium extraction from seawater. In this study, a D-π-A conjugated microporous polymer is synthesized using perylene, phosphonate-containing fluorene, and benzothiadiazole as D, π-linker, and A units, respectively, as novel uranium extraction photocatalysts. Both experimental and theoretical studies have demonstrated that the D-π-A structure simultaneously expands π-electron delocalization and promotes intramolecular charge transfer, thus accelerating the photocatalytic reaction. More importantly, phosphate ester and benzothiadiazole together act as uranyl-affinity “hooks” in the skeleton, adding the asymmetry and expanding the built-in electric field, thereby enhancing the driving force of photogenerated charge separation and elevating the charge separation efficiency (84.8%). The results show that the photocatalytic uranium extraction capacity of CMP-D-π′-A reaches 11.68 ± 0.21 mg g^–1, exceeding most reported photocatalysts. These findings provide a promising avenue for the development of uranium extraction materials through regulating the interfacial electric field.

Poly(2-oxazoline)s (POxs) offer an unparalleled degree of functionalization in the fabrication of smart, functional polymers for a wide range of applications. By utilizing 2-ethyl-2-oxazoline and a unique hydrophobic 2-oxazoline monomer, 2-isostearyl-2-oxazoline, we report the synthesis of a library of functionalized poly(2-ethyl-2-oxazoline)s (PEtOxs) and poly(2-isostearyl-2-oxazoline)s (PiStOxs) that show incredible potential as dispersants of carbon black (CB) in water and dodecane. The initiation and termination of 2-oxazoline polymerizations by direct end-capping can be exploited to introduce a variety of end-groups. Herein, we utilize this methodology to report the efficient synthesis of anthracene-end-capped PEtOx and PiStOx. A small library of 9-(chloromethyl)anthracene-initiated polymers was also synthesized to increase the aromaticity to investigate its influence on the dispersion of CB. The solution behavior of the polymers in aqueous and nonaqueous media is studied via turbidity measurement, and their ability to disperse CB in water and dodecane systems is assessed by a UV–vis spectrophotometer. PEtOx and PiStOx both display characteristics of a good dispersant, and PiStOx exhibits better performance than a commercially available dispersant, presenting superior results than previously reported for POx.

Cross-linked polymers for gas separation have significant advantages in increasing gas selectivity and separation stability. However, the cross-linking strategies unavoidably form permanent interchain covalent bonds and alter the polymer packing state, which largely decrease polymer solubility, static toughness, and reprocessability. Herein, a secondary-amine-containing diamine (HCBDA) derived from carbazole is synthesized and polymerized with 6FDA to furnish a gas-permeable polyimide (HCB-PI) with a pseudo-cross-linked hydrogen-bonding network and a strengthened charge-transfer complex (CTC) effect. Compared with the hydrogen-bonding free sample (CB-PI), HCB-PI displays a more homogeneous micropore distribution and denser chain packing, as is proven by positron annihilation lifetime spectroscopy, which results in enhanced selectivity for O₂/N₂ and CO₂/CH₄ gas pairs and antiplasticization property. Owing to the stronger interaction between the HCB-PI skeleton and molecular oxygen and thus the competitive adsorption mechanism, HCB-PI exhibits more enhanced O₂/N₂ selectivity in mixed-gas measurements (7.54) than in pure-gas measurements (6.58), with the overall separation property approaching the 2008 Robeson upper bound. Additionally, HCB-PI is heat-resistant and mechanically robust, exhibiting static toughness up to 108 MJ·m^–3. Our designing concept for HCB-PI has been demonstrated to be efficacious for oxygen enrichment from air.