Vol.39,

The statistical mechanics of an ideal polymer chain entangled with static topological constraints is studied using a superspace approach, in which the probability distribution of the polymer is obtained as solutions of the Fokker-Planck equation in a superspace with an inner structure characterized by the n-generator free group. The theory predicts that the force-extension curve of the polymer under the topological constraints has the generic form F=kl+Z/l, where l is an effective extension. Aside from the elastic term that is linear in l, the force-extension curve contains a universal term of the form Z/l. The magnitude of this topological term is determined by the topological charge number Z, which characterizes the topological nature of the static constraints. The theoretical results are further verified by a scaling analysis based on a blob model of the chain conformations.

In this work, we demonstrate that the strength of anion specificities of thermosensitive polymers is determined by the affinity of direct anion binding to the polymers. We have prepared a series of thermosensitive statistical copolymers with distinct thermoresponsive behaviors. The anions can specifically interact with the different types of thermosensitive polymers in very different strengths. A similar strength of specific anion effects on thermoresponsive behaviors can be observed at very different salt concentrations for the different types of thermosensitive polymers. A stronger anion binding to the thermosensitive polymers gives rise to a more obvious anion specificity and vice versa. The work presented here opens up opportunities for the application of ion binding affinity to modulate the strength of ion specificities of thermosensitive polymers.

Chirality, commonly found in organisms, biomolecules and nature such as L-amino acids and D-sugars, has been extensively studied in chemistry and biomedical science. Hence, the demand for simple and efficient construction of chiral structures, especially chiral polymers, has been rapidly growing due to their potential applications in chemosensors, asymmetric catalysis and biological materials. However, most chiral polymers reported are prepared directly from chiral monomers/chiral catalysts, the corresponding strategies usually involve tedious and expensive design and synthesis. Fortunately, chirality induction strategies (such as circularly polarized light, chiral solvation and chiral gelation etc.) have been known to be highly versatile and efficient in producing chirality from achiral polymers. In this feature article, the current research on chirality induction, transfer and application in achiral polymer systems is summarized. Furthermore, this article discusses some basic concepts, seminal studies, recent advances, the structural design principles, as well as perspectives in the construction and applications of chiral polymers derived from achiral monomers, with the hope to attract more interest from researchers and further advance the development of chiral chemistry.

With the emergence of multidrug resistance (MDR) in many pathogens, bacterial infections are becoming a growing threat to public health. The frightening scenario is due largely to the formation of biofilms, in which the bacteria are extremely recalcitrant to the conventional antibiotic regimens. To address the emergence of MDR and biofilm-associated infections, numerous polymer-based materials have been designed and prepared recently. The subject of this perspective is the recent development of polymer-based materials that have been applied to combat multidrug-resistant pathogens, to prevent the formation of biofilms, or enhance the eradication efficacy to mature biofilms via killing biofilm-bacteria or dispersing biofilms. The advantages and shortcomings of these polymer-based materials are discussed, as well as the challenges we are facing in the clinical translation of these systems.

In order to overcome the limitation of traditional active nano-therapeutic drugs on tumor targeting efficiency which cannot reach the receptor/target in sufficient amount in the body, in this work, we developed a monoclonal antibody (mAb) and a polymer-hyd-doxorubicin prodrug conjugate, which enables the self-assembled nanoparticles to have precise targeting, tumor tissue aggregation and pH-sensitive drug release. We first prepared an amphiphilic polymer prodrug, abbreviated as H₂N-PEEP-b-PBYP-hyd-DOX, via a combination of ring-opening polymerization (ROP) and “click” chemistry, in which PEEP and PBYP represent two kinds of phosphoester segmemts, -hyd- is hydrazone bond. After self-assembly into prodrug nanoparticles (PDNPs) with a diameter of about 93 nm, CD147 mAb was conjugated onto the PDNPs by EDC/NHS chemistry to form mAb-PDNPs. For the PDNPs and mAb-PDNPs, we also investigated their stability, in vitro drug release behavior and cellular uptake. The results showed that the pH-responsive PDNPs can remain relatively stable under the condition of PB 7.4 buffer solution. However, under acidic conditions or in the presence of phosphodiesterase I (PDE I), both the amount and rate of DOX release increased at the same incubation period. Cytotoxicity assay showed that mAb-PDNPs exhibited higher cytotoxicity (IC₅₀: 1.12 mg·L⁻¹) against HepG2 cells than PDNPs (IC₅₀: 2.62 mg·L⁻¹) without monoclonal antibody. The nanoparticles with antibodies mAb-PDNPs have relatively better stability and can directly achieve the targeting drug delivery through CD147 mAb.

1,2-Dioxetane is a well-known chemiluminescent mechanophore allowing real-time monitoring of polymer chain scission, but usually suffers from fluorescence quenching in polar environments. Herein, a series of mechanochemiluminescent waterborne polyurethanes/carbon dots composites (WPU-CDs) have been synthesized by incorporating fluorescent CDs to promote the energy transfer process in different environments. The resulting bulk WPUs, and in particular, their swollen films filled with a large amount of polar solvents (water and ionic liquid) emit intense mechanochemiluminescence. Thus force-induced covalent bond scission and stress distribution within these different WPU-CDs films can be sensitively visualized. Furthermore, the ionic liquid containing films exhibited both electrical and luminescent signal changes under stretching, which offer a new kind of force sensor responsive at a broad detecting strain range and for multi-mode strain analysis. This study is expected to stimulate new research endeavors in mechanistic insight on waterborne polyurethanes and the corresponding stretchable sensing devices.

Fluorescence imaging has been an indispensable tool to provide dynamic information about the localization and quantity of organisms. Meanwhile, due to the intrinsic hollow structure and modularized biofunctionalities, polymer vesicles have been widely applied in biomedical field. However, most polymer vesicles are embedded with organic fluorophores for fluorescence imaging, which have certain drawbacks such as leakage and possible cytotoxicity. Here, we present a biodegradable polypeptide-based vesicle with intrinsic blue fluorescence without introducing any fluorophore for real-time visualization of antibacterial process. Through modular design to integrate multiple functional fragments, poly(ε-caprolactone)-block-poly(tryptophan)-block-poly(lysine-stat-phenylalanine) [PCL₂₅-b-PTrp₂-b-P(Lys₁₃-stat-Phe₄)] was synthesized, where PCL chains form the hydrophobic membrane, P(Lys-stat-Phe) and PTrp provide intrinsic fluorescence and broad-spectrum antibacterial activity. It is noteworthy that the fluorescence emission was shifted from invisible ultraviolet range of amino acids to visible range (emission maximum at 436 nm), which makes it possible to visualize the antibacterial process. In addition, through utilizing the intrinsic fluorescence of vesicles, confocal fluorescent imaging of vesicles with bacteria validated the specific adhesion of vesicle towards bacteria, and the bacterial death through membrane disruption. Overall, we provided a novel approach to developing biodegradable fluorescent polypeptide-based vesicles for real-time visualization of antibacterial process.

In recent years, the hydrogel-based tissue adhesives have been extensively investigated for their excellent biocompatibility and the ability to be administered directly within the adherent tissue. To meet the requirement for more controllable release in various physiological settings, the components of hydrogel adhesive should be more precisely tailored. In this work, the POSS-ace-PEG hydrogel adhesive was fabricated with the polyacetal dendrimer G1'-[NH₃Cl]₁₆ and poly(ethylene glycol) succinimidyl carbonate (PEG-SC) due to the regular peripheral amino structure of G1'-[NH₃Cl]₁₆. Rheological and adhesion tests demonstrated that the hydrogel adhesive had good mechanical and adhesive properties, which could effectively adhere to the pigskin and severed nerves. Moreover, the tissue adhesive exhibited good stability under neutral conditions and the rapid degradation under acidic conditions, allowing for the release of doxycycline hydrochloride (DOX) drug in response to pH. Together, these results suggested that the POSS-ace-PEG adhesive had the potential to provide an alternative to tissue adhesives for applications in pathological environments (inflammation, tumors, etc.).

In consideration of various advantages such as less harm, higher sensitivity, and deeper imaging depth, etc., AIE materials with long-wave emission are attracting extensive attention in the fields of vascular visualization, organelle imaging, cells tracker, forensic detection, bioprobe and chemosensor, etc. In this work, a novel fluorescent (R)-PVHMA monomer with chirality and aggregation-induced emission enhancement (AEE) characteristics was acquired through enzymatic transesterification reaction basing on phenothiazine, and its \begin{document}${\left[\alpha \right]}_{D}^{25^\circ {\rm{C}}}$\end{document} value was about −6.39° with a 3.08 eV bandgap calculated by the quantum calculations. Afterwards, a series of PEG-PVH1 and PEG-PVH2 copolymers with chirality feature were achieved through RAFT polymerization of the obtained (R)-PVHMA and PEGMA with various feed ratios. When the feed molar ratio of (R)-PVHMA increased from 21.5% to 29.6%, its actual molar fractions in the PEG-PVH1 and PEG-PVH2 copolymers accordingly increased from 18.1% to 25.7%. The molecular weight of PEG-PVH1 was about 2.2×10⁴ with a narrow PDI, and their kinetics estimation showed a first-order quasilinear procedure. In aqueous solution, the amphiphilic copolymers PEG-PVH could self-assemble into about 100 nm nano-particles. In a 90% water solution of H₂O and THF mixture, the fluorescence intensity had the maximum value, and the emission wavelength presented at 580 and 630 nm. The investigation of cytotoxicity and cells uptake showed that PEG-PVH FONs performed outstanding biocompatibility and excellent cells absorption effects, which have great potential in bioimaging application.

The flexibility of organic photovoltaics (OPVs) has attracted worldwide attention in recent years. To realize the bending-stability of OPVs, it is necessary to put forward the bending-stability of interfacial layer. A novel bendable composite is explored and successfully applied as an electron transport layer (ETL) for fully-flexible OPVs. We incorporated poly(vinylpyrrolidone)(PVP) into conjugated electrolytes (CPE) to composite a bendable ETL for high-performance OPVs devices. Fortunately, the devices based on PVP-modified CPE exhibited better device performances and more excellent mechanical properties of bendability. The fullerene-free OPVs based on PM6:IT-4F with CPE@PVP as ETLs yield the best power conversion efficiency (PCE) of 13.42%. Moreover, a satisfying efficiency of 12.59% has been obtained for the fully-flexible OPVs. As far as we know, this is one of the highest PCE for fully-flexible OPV based PM6:IT-4F system. More importantly, the flexible OPVs devices can retain more than 80% of its initial efficiency after 5000 bending cycles. Furthermore, among various curvature radii, the mechanical properties of the device based on CPE@PVP are superior to those of the device based on bare CPE as ETL. These findings indicate that the functional flexibility of CPE as a cathode interfacial layer is an effective strategy to fabricate high-performance flexible devices in the near future.

In all-polymer solar cells (APSCs), number-average molecular weights (M_ns) of polymer donors and polymer acceptors play an important role in active layer morphology and photovoltaic performance. In this work, based on a series of APSCs with power conversion efficiency of approaching 10%, we study the effect of M_ns of both polymer donor and polymer acceptor on active layer morphology and photovoltaic performance of APSCs. We select poly[4-(5-(4,8-bis(5-((2-butyloctyl)thio)thiophen-2-yl)-6-methylbenzo[1,2-b:4,5-b']dithiophen-2-yl)thiophen-2-yl)-5,6-difluoro-2-(2-hexyldecyl)-7-(5-methylthiophen-2-yl)-2H-benzo[d][1,2,3]triazole] (CD1) as the polymer donor and poly[4-(5-(5,10-bis(2-dodecylhexadecyl)-4,4,9,9-tetrafluuoro-7-methyl-4,5,9,10-tetrahydro3a,5,8,10-tetraaza-4,9-diborapyren-2-yl)thiophen-2-yl)-7-(5-methylthiophen-2-yl)benzo[c][1,2,5]thiadiazole] (PBN-14) as the polymer acceptor. The M_ns of polymer donor CD1 are 14.0, 35.5 and 56.1 kg/mol, respectively, and the M_ns of polymer acceptor PBN-14 are 32.7, 72.4 and 103.4 kg/mol, respectively. To get the desired biscontinueous fibrous network morphololgy of the polymer donor/polymer acceptor blends, at least one polymer should have high or medium M_n. Moreover, when the M_n of polymer acceptor is high, the active layer morphology and APSC device performance are insensitive to the M_n of polymer donor. The optimal APSC device performance is obtained when the M_n of both the polymer donor and the polymer acceptor are medium. These results provide a comprehensive and deep understanding on the interplay and the effect of M_n of polymer donors and polymer acceptors in high-performance APSCs.

Introducing small molecule-bridged hydrogen bonds (HBs) between polymer chains has been reported to effectively reduce the inter-chain cooperativity despite of strengthening the intermolecular interaction. Here, a systematic investigation on tuning the Johari-Goldstein β (β_JG) relaxation by adding various low-molecular-weight phenols in poly(n-alkyl methacrylate)s is carried out to further clarify the anomalous dynamics. Given these small molecules capable of coupling the motion with pendent groups of host polymers due to forming at least two HBs per molecule, poly(n-alkyl methacrylate) mixtures exhibit rich dynamic changes in the β_JG-properties and α, β_JG separations. An increased loading of phenols with a small size and strong inter-HB strength (Δυ_i) clearly benefits for significant retardation and suppression of the β_JG-relaxation, narrows the α, β_JG separation and converges the β_JG-peak with the α-peak, which demonstrates the alleviation of inter-chain topological constraints. However, small molecules with a relatively big size and weak Δυ_i are found to amplify the magnitude of the α, β_JG separation of poly(butyl methacrylate), even though experimental results of changes in α-dispersion and dynamic fragility confirm a reduction of the coupling factor n in all of these hybrids. The counterintuitive phenomenon suggests that the crossover time t_c in the Coupling Model is no longer a universal quantity if the inter-chain interaction of polymers is strengthened by HBs. These compelling findings shed vital insights into the HB-induced anomalous dynamics, and provide essential guidance for tailoring the β_JG behavior and designing glassy polymeric materials.

Stereocomplex-type polylactide (SC-PLA) consisting of alternatively arranged poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) chains has gained a good reputation as a sustainable engineering plastic with outstanding heat resistance and durability, however its practical applications have been considerably hindered by the weak SC crystallizability. Current methods used to enhance the SC crystallizability are generally achieved at the expense of the precious bio-renewability and/or bio-degradability of PLAs. Herein, we demonstrate a feasible method to address these challenges by incorporating small amounts of poly(D,L-lactide) (PDLLA) into linear high-molecular-weight PLLA/PDLA blends. The results show that the incorporation of the atactic PDLLA leads to a significant enhancement in the SC crystallizability because its good miscibility with the isotactic PLAs makes it possible to greatly improve the chain mixing between PLLA and PDLA as an effective compatibilizer. Meanwhile, the melt stability (i.e., the stability of PLLA/PDLA chain assemblies upon melting) could also be improved substantially. Very intriguingly, SC crystallites are predominantly formed with increasing content and molecular weight of PDLLA. More notably, exclusive SC crystallization can be obtained in the racemic blends with 20 wt% PDLLA having weight-average molecular weight of above 1×10⁵ g/mol, where the chain mixing level and intermolecular interactions between the PLA enantiomers could be strikingly enhanced. Overall, our work could not only open a promising horizon for the development of all SC-PLA-based engineering plastic with exceptional SC crystallizability but also give a fundamental insight into the crucial role of PDLLA in improving the SC crystallizability of PLLA/PDLA blends.

Herein, isotactic polypropylene films with small β-nucleating agent content were fabricated via a melt-extrusion-stretched technology with intended “shear-free” in barrel and die. Compared with neat films, the tensile strength, elongation at break and strain energy density at break of iPP film with 0.05 wt% β-nucleating agent are significantly improved by 13.8%, 39.6% and 90.6%, respectively, indicating the simultaneously enhanced toughness and strength. Additionally, the β-crystal content gradually increases with increasing β-NA content, while the relative total daughter content of α- and β-crystal exhibits opposite tendency. Moreover, nucleation and crystal growth induced by various β-NA contents are different. This work proves an efficient strategy to enhance mechanical properties of isotactic polypropylene film via controlling elongation flow and addition of appropriate β-NA content.

We propose a unified thermodynamic model of flow-induced crystallization of polymer (uFIC), which incorporates not only the conformational entropy reduction but also the contributions of flow-induced chain orientation, the interaction of ordered segments, and the free energy of crystal nucleus and crystal morphology. Specifically, it clarifies the determining parameters of the critical crystal nucleus size, and is able to account for the acceleration of nucleation, the emergence of precursor, different crystal morphologies and structures induced by flow. Based on the nucleation barrier under flow, we analyze at which condition precursor may occur and how flow affects the competition among different crystal forms such as orthorhombic and hexagonal phases of polyethylene. According to the uFIC model, the different crystal morphologies and structures in the flow-temperature space have been clarified, which give a good agreement with experiments of FIC.

We performed dynamic Monte Carlo simulations of stress relaxation in parallel-aligned and uniaxially stretched bulk amorphous polymers at low temperatures. We observed an extra-slowing down in the early stage of stress relaxation, which causes nonlinear viscoelasticity as deviated from Debye relaxation and Arrhenius-fluid behaviors observed previously at high temperatures. Meanwhile, fluctuation analysis of stress relaxation revealed a substantial increase in the stretch fractions of polymers at the transient periods of high-temperature Debye relaxation. Structural analysis of free volume further revealed the scenario that, at low temperatures, the modulus of polymer entropy elasticity decreases with temperature and eventually loses its competition to the imposed modulus (Deborah number becomes larger than one), and hence upon stress relaxation under constant strains, monomers are firstly accumulated nearby two stretching ends of polymers, resulting in tentative global jamming like physical cross-linking there, and thus retarding the coming transient state of stress relaxation. We concluded that intermolecular cooperation raises physical crosslinking for nonlinear viscoelasticity of polymer stress relaxation as well as the rubbery states unique to bulk amorphous polymers. The new microscopic mechanism of the fluid-rubbery transition of polymers may bring insights into the intermolecular cooperation mechanism of glass transition of small molecules, if the fluid-rubbery transition is regarded as an extrapolation of glass transition from low to high molecular weights.

We employed the extended self-consistent field theory to investigate the supramolecular self-assembly behaviors of asymmetric diblock copolymer blends (AB/B’C) with hydrogen bonding interactions between shorter B and B’ blocks. The hydrogen bonding interactions are described by Yukawa potentials, where the hydrogen bonding donors and acceptors were modelled as two blocks smeared with opposite screened charges. The hierarchical microstructures with parallelly packed lamellae-in-lamellae (Lam) and 4.8.8 Archimedean tilting pattern (4.8.8) were observed at lower and higher hydrogen bonding density (θ), respectively. The hierarchy of Lam and 4.8.8 were demonstrated by the one- and two-dimensional density profiles and the underlying order of the large-length-scale and small-length-scale microstructures were also clarified. It was found that the 4.8.8 is favorable to the stronger hydrogen bonding density or interactions. As θ increases, the microphase transition from Lam to 4.8.8 occurs at θ=0.34, which is mainly attributed to the optimization of the electrostatic energy and conformational entropy with sacrificing the interfacial energy. This work can provide a new strategy to understand the supramolecular self-assembly as well as the mechanism behind the formation of complex hierarchical microstructures.

We present a novel generating function (GF) method for the self-condensing vinyl polymerization (SCVP) system with any initial distribution of preexisted polymers. Such a method was proven to be especially useful to investigate the semi-batch SCVP system allowing a sequence of feeding operations during the polymerization. Consequently, the number-, weight-, and z-average molecular weights as well as dispersity index of hyperbranched polymers can be explicitly given, which are determined by predetermined feeding details and conversions in each polymerization step. These analytical results are further confirmed by the corresponding Monte Carlo simulations. Therefore, the present GF method has provided a unified treatment to the semi-batch SCVP system. Accordingly, hyperbranched polymers with desired properties can be prepared by designing feeding details and presetting conversions at each step based on the present GF method.

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