This work reports the structural feature and internal motion of one novel hyperbranching cluster system in dilution solution. The cluster system is composed of HB-PS₃₀₀-g-PtBA₄₅ hypergraft copolymer chains with uniform subchain, high molar mass and low polydispersity (M_w=1.73×10⁶ g/mol and < M_w/M_n>≈1.07), where HB-PS and PtBA represent hyperbranched polystyrene core and poly(tert-butyl polyacrylate) graft, respectively. In the selective solvent of PS blocks (cyclohexane, T_θ=34.5 °C), the aggregation kinetics and structural feature are found to be precisely tunable for assembled clusters by the aggregation temperature (11 °C<T<17 °C) and time (0 h<t<24 h). An interesting structural evolution kinetics is observed, namely, the fractal dimension (d_f) of clusters is found to first increases and then decreases with t, eventually, it reaches a plateau value of d_f≈3.0, corresponds to a uniform spherical structure. By using dynamic light scattering (DLS) to monitor the number and strength of relaxation modes in Γ(q) with Γ being the decay rate and q being the scattering vector, it is quantitatively revealed that the relaxation, intensity contribution and mode origin of internal motions of clusters are neither similar with previously reported cluster systems with high polydispersity, nor with the classical linear chain systems. In particular, in the broad range of 2.0<qR_h<6.0, we have observed that the reduced first cumulant [Γ* = Γ(q)/(q³k_BT/η₀)] does not display an asymptotic behavior. Whereas, a better asymptotic behavior is observed by plotting Γ(q)/q⁴ versus qR_h. For the first time, our observation provides direct evidence supporting that, for hyperbranching cluster system with low polydispersity and high local chain segment density, the hydrodynamic interaction is greatly weakened due to the enhanced hydrodynamic shielding effect.

Flexibility is the most prominent advantage of organic solar cells (OSCs) compared with traditional photovoltaic devices, showing an irreplaceable commercial potential. Currently, the maximum power conversion efficiencies (PCEs) of single-junction OSCs have been over 19% and 16% upon rigid and flexible substrates, respectively, which meet the criteria for commercial application. Extensive research efforts are under way, such as device configuration design, interface/photosensitive layer synthesis, transparent electrode modification and printing technology innovation, however, the reasonable selection of printing technologies, the huge performance loss of large-area printing process and the structural design of flexible modules are still the bottlenecks, limiting the commercialization of OSCs. This review focuses on the technical challenges and rational modular configuration design for printing preparation of flexible high-efficiency large-area organic devices, from the aspects of the functional layer material selection, printing process research status and large-scale efficiency losses. These will promote the integrated applications of printable organic semiconductor materials for next-generation clean energy and appeal extensive attentions in wearable electronics, building-integrated photovoltaics and Internet of Things, etc.

Recently, hyperbranched polymers (HBPs), which differ significantly in structure and properties from linear, cross-linked and branched analogs, have become increasingly important. HBP have a spatial unloaded core and a shell of branched monomer units (dendrons), in which functional groups are predominantly located in the surface layer. The size of macromolecules ranges from 2 nm to 100 nm. Currently, there are a fairly large number of publications in the literature devoted to the modification of hyperbranched polyester polyols with various functional groups and the assessment of the potential for their use. However, there are no review articles on this topic in recent years. In this regard, it is relevant to generalize the latest achievements in the field of synthesis, properties and application of hyperbranched polyester polyols with terminal oxygen, nitrogen, silicon, sulfur and organophosphorus fragments. The advantage of hyperbranched polyester polyols of the Boltorn H series is their industrial availability, biodegradability, nanoscale, non-toxicity and high solubility in various polar solvents due to short monomer units, as well as the presence of reactive terminal hydroxyl groups. Functionalization of hyperbranched polyester polyols at hydroxyl groups is mainly carried out by addition of acid anhydrides, iso(thio)cyanates, alkenes, lactides, lactones, lactams, epoxy compounds or reactions with halogenated compounds (alkyl halides, acid chlorides). In some cases, for the functionalization of polyester polyols special linkers are used, such as acid chlorides of unsaturated or dicarboxylic acids, diisocyanates, etc., which provide covalent bonding of the hyperbranched polymer with the target functional group. The obtained derivatives of hyperbranched polyesters are widely used in such areas as biomedicine, pharmacy, paints and varnishes, they are also used as catalysts, membranes, multifunctional coatings, plasticizers and polymer stabilizers.

In recent years, non-fullerene acceptors (NFAs) with unfused-ring structure have received extensive attention due to their flexible combination of building blocks and relatively simple synthetic routes. In this work, three new A-D-C-D-A type unfused-ring acceptors (UFAs), named DTBTzEH-IC2F, DTBTzMe-IC2F and DTBTzMe-IC2Cl, were designed and synthesized with dithienobenzotriazole (DTBTz) as the core. Through modification of alkyl chain on the DTBTz unit and change of halogen atoms on the cyanoindanone end groups, the differences in optoelectronic properties of these three small molecule acceptors were investigated. The results show that changes in alkyl chain and halogen atom endow UFAs with different features, including shift in absorption, changes in energy level and molecular packing. When blended with donor PBDB-T, the organic solar cell based on DTBTzMe-IC2Cl achieves the highest device efficiency of 12.3%, while DTBTzEH-IC2F-based device obtains 11.5% efficiency and DTBTzMe-IC2F-based device obtains 12.0% efficiency. The stability tests show that all the devices obtain good efficiency retention rates. These results demonstrate that the introduction of a rigid aromatic ring DTBTz as an intermediate core not only effectively results in highly planar A-D-C-D-A small molecules, but also provides a new reference for the design and development of UFAs in OSCs.

The power conversion efficiency (PCE) of polymer solar cells (PSCs) has exceeded 19% due to the rapid progress of photoactive organic materials, including conjugated polymer donors and the matched non-fullerene acceptors (NFAs). Due to the high density of oxygen vacancies and the consequent photocatalytic reactivity of ZnO, structure inverted polymer solar cells with the ZnO electron transport layer (ETL) usually suffer poor device photostability. In this work, the eco-friendly glucose (Glu) is found to simultaneously improve the efficiency and stability of polymer:NFA solar cells. Under the optimal conditions, we achieved improved PCEs from 14.77% to 15.86% for the PM6:Y6 solar cells. Such a PCE improvement was attributed to the improvement in J_SC and FF, which is ascribed to the smoother and more hydrophobic surface of the ZnO/Glu surface, thereby enhancing the charge extraction efficiency and inhibiting charge recombination. Besides, UV-Vis absorption spectra analysis revealed that glucose modification could significantly inhibit the photodegradation of Y6, resulting in a significant improvement in the stability of the device with 92% of its initial PCE after aging for 1250 h. The application of natural interface materials in this work brings hope for the commercial application of organic solar cells and provides new ideas for developing new interface materials.

The manipulation of the morphology of the active layers is crucial for improving the performance of organic photovoltaic (OPV) devices. In particular, the development of non-fullerene acceptors (NFAs) has led to a large number of new materials with more complex interactions. Therefore, the investigation on the morphology control mechanism is the key aspect in providing guidance for material design and device optimization. In this study, the film morphology optimization using 1,8-diiodooctane (DIO) additive and a ternary fullerene acceptor strategy have been carried out based on the PCE10:ITIC blends. It is seen that suitable amount of DIO helps to increase the crystallization of the blended thin film. However, excessive DIO elevates the crystallization-induced phase separation and the domain size can exceed the exciton diffusion length, leading to efficiency drop. The addition of fullerene acceptor can improve the carrier transport of the blends, and its presence could retard the excessive phase separation induced by DIO additive. Under the joint optimization of the solvent additive and PC₇₁BM acceptor, the film morphology achieves a balance between crystallization and phase separation scales, the exciton diffusion and carrier transport are also optimized, and the short-circuit current (J_SC) and fill factor (FF) of the device can be improved significantly.

Due to their dynamic nature and strength tunability, metallo-supramolecular polymers have been introduced into various materials. The mechanical strength of the metallo-supramolecular polymers in the system directly influences the mechanical properties (e.g., the toughness) of the materials. Therefore, it is necessary to explore the mechanical behavior of the metallo-supramolecular polymers. Herein, we present a single-molecule method to systematically explore the chain structure and mechanical properties of metallo-supramolecular polymer by using a loop protected architecture. Notably, we found that the mechanical stability of the individual chain, which is determined by the strength of terpyridine-Fe²⁺-terpyridine (tpy-Fe²⁺-tpy) bonds, was about 0.6–1.0 nN, depending on the pulling speed. This value is around three times higher than those measured using old methods. In addition, the unique loop protected structure further reduces the interference of non-specific polymer-AFM tip (or polymer-substrate) interactions on the quantification of the actual strength and kinetic parameter of noncovalent interactions in supramolecular polymers. Furthermore, the single chain flexibility of the metallo-supramolecular polymer was investigated and found to be comparable to the corresponding covalent analogues. Our findings provide a new way to explore the force response of supramolecular polymers composed of metal-ligand interactions and will be useful for the design of metallo-supramolecular polymer-based functional materials with tailored mechanical properties.

Exploring new polymerization strategy for current available monomers is a big challenge in polymer science. Here we re-investigate radical polymerization of monovinyl monomer (MVM) initiated by uniform branched polyfunctional initiator (PFI), which is termed non-linear radical additions-coupling polymerization (NLRAsCP). In NLRAsCP, both addition and coupling reactions of radical contribute to the construction of the polymer chains, which leads to continuous growth of branch topology. Theoretical analysis of NLRAsCP predicts that the gelation is determined by the functionality of PFI (a), the extent of initiation of the PFI (q) and the termination factor of radical (φ). NLRAsCPs of styrene and methyl methacrylate promoted by Cu(0)/Me₆TREN or Mn₂(CO)₁₀/visible light were conducted. After the cleavage of incorporated PFI fragment or junctions in the network, the network was transformed to linear chains having almost the same structure as segmental chains in the precursor network. This allows the reverse deducing the network structure from its cleaved products. It has been proven that NLRAsCP includes stepwise initiation of PFI, chain-growth of segmental chains and successive endlinking of macroradicals derived from PFI. The three parameters related to the gelation process, a, qand φ, were adjusted via binary PFI, the feed ratio of [Mn₂(CO)₁₀]/[PFI] and addition of non-homopolymerizable comonomer respectively. The minimum values ofa and q, and the minimum amount of comonomer required for gelation were determined, which can be applied to estimate φ of various macroradicals. NLRAsCP opens a general and facile strategy for synthesis of a variety of polymer networks with heritable architecture by one-pot polymerization of various MVMs.

The formation of homopolypeptide vesicles and the identification of their self-assembly mechanism have been challenging issues in the field of polymer self-assembly. Using complementary circular dichroism (CD), Fourier transform infrared (FTIR) and low-field nuclear magnetic resonance (LF-NMR) spectroscopies, in this study we show that the higher hydrophilic ability of side-chains is a key factor for the formation of homopolypeptide vesicles from homo poly(Nε-carbobenzoxy-L-lysine) (PZlys), in which the vesicular structures are confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) measurements. Poly(γ-benzyl-L-glutamate-co-Nε-carbobenzoxy-L-lysine) [P(BLG-co-Zlys)] containing different molar ratios of BLG to Zlys units with the same peptide backbone as PZlys are used as the controls. The copolypeptides can only form micelles under the same conditions, due to the more hydrophobic nature of their side-chains. These results show that the specific side-chain structure of the polypeptides plays a fundamental role in the self-assembly of homopolypeptides. These findings can be useful to understand how the hydrophilicity of the side chains of amino acid residues on the surface of a protein affects its structures.

We propose a theoretical approach to quantitatively account for the role of entanglement in the nucleation of polymer melts, which is the unique feature of polymer differentiated from small molecules. By performing molecular dynamics simulations, we obtain the nucleation barriers of polymer systems with different entanglement densities, which exhibits an opposite trend compared to the prediction of the classic nucleation theory (CNT). To amend the deficiency of the CNT in polymer crystallization, we introduce the entanglement free energy to reflect the role of entanglement in polymer nucleation. Specifically, the polymer nucleation not only involves free energies of monomers inside and on the surface of a nucleus as considered in the CNT, but also affects the entanglement network around the nucleus. Our theoretical approach provides a reasonable interpretation for the unsolved nucleation phenomena of polymers in simulations and experiments.

Polyimide films derived from representative PMDA/ODA were prepared with thickness ranging from 5 μm to 25 μm, and the effect of aggregation structure on thermal expansion behavior along different directions was studied. Both in-plane and out-of-plane linear thermal expansion (CTE_// and CTE$_\perp $) were respectively characterized by thermal mechanical analysis and FT-near-IR interference method. Volumetric and anisotropic behavior of thermal expansion were also investigated. With increasing film thickness, CTE_// gradually increased from 32.2 ppm/°C to 46.1 ppm/°C while CTE$_\perp $ decreased from 149.7 ppm/°C to 128.2 ppm/°C. Volumetric thermal expansion of polyimide films was less sensitive to the varied thickness, but anisotropy of thermal expansion was reduced. Polyimide film of 5 μm thickness showed large birefringence, indicating more considerable in-plane chain orientation anisotropy. Besides, molecular chains were more densely packed along in-plane direction when film thickness increased, while became loosely stacked in the out-of-plane direction. In contrast to the enhanced lateral chain packing for thicker films, higher vertical chain packing order was found in thinner films. The variation of aggregation structure during thermal expansion procedure was analyzed by temperature-dependent WAXD. It is proved that thermal expansion behavior of thinner films could be largely attributed to molecular chain packing, whereas that may be influenced by many factors for thicker films in addition to the effect of chain packing. The results revealed that thermal expansion of films with thickness variation is closely related to molecular chain orientation and packing, which is associated with both chemistry and morphological structure of polyimide.

The stress relaxation of semi-crystalline nylon 1010 cannot be fitted by the Kohlrausch-Williams-Watts formula when the experiments were performed at pre-yielding regime below the glass transition temperature. We study this problem and identify the two-step mechanism of stress relaxation. At short time scale, relaxation is fast, dominated by stress biased thermal fluctuation with a fixed short-range length scale (activation volume). At long time scale, relaxation is slow due to the emergence of a cooperative long-range length scale determined by the stress fluctuation. The cooperative length scale is proportional to the reciprocal of stress and the amplitude of stress fluctuation is the product of stress and activation volume. Based on this two-step mechanism, we propose a new kinetics equation to capture the stress relaxation effectively, where the short time relaxation is described by an Eyring-like local activation and the long-time relaxation is captured by a cooperative excitation process resorting to an extension from the random first order transition theory. Our equation fits the experimental data well and can serve as a model to guide the related experiments of relaxation processes in crystalline solids.

Recent studies indicate that active polymers often show curious conformational and dynamical properties. Specially, rigid polymers with self-propelled tangential forces can move directionally and even push a cargo. Motivated by this, the translocation of an active bead-spring polymer through a narrow pore is studied simulationly in this work. Each bead of the polymer is propelled by a tangential active force (f_a) along the contour of the polymer. Simulation results show that the active polymer translocates through the pore in a railway-motion manner. The translocation velocity ν of the polymer is determined only by f_a, resulting that the translocation time (τ) as a function of the polymer length (N) and the active force f_a can be expressed as $ \tau \propto N{f}_{\mathrm{a}}^{-1} $, which is independent of the rigidity of the polymer. Our results indicate that the translocation dynamics of active polymers is quite different from that of passive polymers.

The dynamic behaviors of a single vesicle bounded by the cylindrical wall in a Poiseuille flow were investigated by considering different confinements and dimensionless shear rates. By observing the evolution of two adjacent particles attached to the internal and external surfaces of the spherical vesicles, we found they had the same frequency. The vorticity trajectories formed by the time-tracing of the particles on the membrane are parallel, which can be identified as the unsteady rolling motion of the membranes due to the unfixed axis. The dynamic behaviors of vesicles are associated with the confinement degree and the dimensionless shear rate. The smaller dimensionless shear rate will result in the slower frequency of the rolling by examining the velocity of the rolling. The weakened rolling motion under stronger confinements is observed by measuring the evolution of the orientation angles. The changes of revolution axes over time can be interpreted by the lateral excursion of the center of mass on the orthogonal plane of the flow.

Polypropylene (PP) sheets are cast with various chill roll temperatures and rates, which are studied with differential scanning calorimetry, wide angel X-ray diffraction, scanning electronic microscopy and dielectric withstand voltage test system. The results show that increasing the chill roll temperature and cast rate can promote the increase of crystallinity and the growth of β-form. The PP sheets have asymmetric skin layer structures. The lower the chill roll temperature, the thicker the skin layer, the smaller the spherulite size. The electric breakdown strength (E_b) of PP sheets is mainly affected by the crystallinity but not the morphology. The PP sheets are further stretched to prepare bi-axially oriented PP (BOPP) films with various heat setting time. Our results indicate that the structure of PP sheets affects the properties of BOPP films. The as prepared BOPP films from the sheets cast at high chill roll temperature and rate have the highest crystallinity and E_b. Heat setting time has profound effect on the crystallinity and E_b, which increase first and then decrease with the heat setting time. It is expected that our study can provide guidance for optimizing process parameters.

Polymers with reversible plasticity shape memory effect (RPSME) have attracted considerable attention due to their simple programming and large deformation. However, the exact mechanisms of RPSME are still not thoroughly understood. In this work, the RPSME of SEBS/crystallizable paraffin was investigated by comparatively analyzing the performances and microstructures of samples with different paraffin content. It was found the shape fixing ratios (R_fs) of samples increased with the paraffin content, and interestingly, a significant improvement in R_f was observed when the paraffin content exceeded 60 wt%. Tensile test results showed that the deformation characteristics of samples changed from elastic to plastic as the paraffin content increased above 60 wt%. By exploring the crystallization behaviors of paraffin in various SEBS/paraffin samples, it was revealed that the microstructures of SEBS/paraffin were different when the paraffin content was below 50 wt% and above 60 wt%. In samples with low paraffin content (below 50 wt%), nearly all paraffin was co-crystallized with ethylene-co-butylene (EB) chains and its crystallization was severely restricted; while in samples with high paraffin content (above 60 wt%), “excess” paraffin appeared and this part of paraffin crystallized on the template of the EB/paraffin co-crystals, which might be responsible for the elastic-to-plastic transition and the sharp increase in R_f. Based on the above results, a possible structural model was proposed to explain the exact mechanism of RPSME in SEBS/paraffin.