Multi-polymerization in which different polymerization mechanisms are performed together serves as an essential synthetic methodology for the construction of polymers with specific architectures, constitutions, and properties. Compared to single mechanism polymerization, the scope of multi-polymerization is significantly broadened by both the available synthetic methods and the synthesized polymeric materials. In this mini-review, multi-polymerizations are categorized into three major types based on the logical relationship between different mechanisms: sequential/tandem polymerization, orthogonal/concurrent polymerization, and hybrid polymerization. Each type of multi-polymerization is briefly introduced and summarized. This mini-review also discussed the importance of mutual influence in multi-polymerization and the potential research interests in this field.

The recently emerged double-cable conjugated polymers have come into focus due to their significantly improved power conversion efficiencies (PCEs) in single-component organic solar cells (SCOSCs). In this work, the effect of chlorination in double-cable conjugated polymers with linear benzodithiophene backbone and pendant perylene bisimide on the photovoltaic performance in SCOSCs has been studied. After introducing chlorine atoms into conjugated side chains, the highest occupied molecular orbital level of the conjugated polymers is down-shifted, thus resulting in a higher open-circuit voltage. As a result, the chlorinated double-cable conjugated polymer exhibits improved photovoltaic performance from 3.46% to 3.57%.

The use of additive is an effective approach to optimize the active layer morphology and improve the power conversion efficiency (PCE) of organic solar cells (OSCs). However, residual solvent additives always lead to undesirably compromise the stability of OSCs. In this work, an organic small molecule BBT-Cl was designed and used as a novel solid additive to partly replace solvent additive to fabricate high-performance OSCs. The synergistic effect of the dual additives on the optical property, morphology and photovoltaic characteristics of the PM6:Y6 based non-fullerene OSCs have been systematically characterized. The introduction of BBT-Cl could effectively enhance the crystallinity of the blend and promote charge extraction and transport. Consequently, the OSCs processed by the dual additives exhibit a high PCE of 17.73%, which is obviously higher than OSCs with CN additive (16.48%). Meanwhile, BBT-Cl based dual additives treatment has also been successfully introduced into another two non-fullerene OSCs to verify its general applicability. Furthermore, 20% PCE aging is significantly prolonged from 720 min to 2880 min for the devices proceeded with the dual additives. This work highlights the great potential of solid additive in the fabrication of efficient OSCs with excellent stability.

The hole transport layer (HTL) affects the device performance and stability of organic solar cells. In this work, a stable molybdenum oxide (MoO_x) hole transport layer with low cost was prepared by adjusting the state of the precursor solution with an alcoholic solution of molybdenum acetylacetonate through an oxidant. The MoO_x transport layer has good transmittance with a work function of 5.07 eV and higher surface energy. The PM6:Y6 devices using MoO_x HTL achieve a high efficiency of 16.8%. MoO_x HTL exhibits good applicability with excellent performance in both ternary and all-polymer systems. Air storage stability T₈₀ of the all-polymer device using MoO_x HTL was over 600 h, much higher than 70 h of the PEDOT:PSS-based device, and its thermal stability at 85 °C and operational stability under light show better stability than that of the PEDOT:PSS hole transport layer. This work provides a facile and low-cost method to fabricate HTL for organic solar cells, which is beneficial to improve their efficiency and stability.

In this study, a zwitterionic polymer/liquid crystals composite film with programming shape-morphing behavior and humidity-responsive self-healing performance was prepared by blending a zwitterionic polymer and liquid crystalline azobenzene compound in solution, followed by film-forming in a mold without tedious or multistep synthetic route. The as-obtained zwitterionic polymer/liquid crystal composite film exhibited programming shape-morphing behavior under different stimuli. In this process, the temporary shape of the composite film was memorized after the removal of the stimuli. Such characteristics would fit the requirements of intelligence and energy-saving for stimuli-responsive shape-changing materials. Moreover, the composite film showed humidity-responsive self-healing performances under wet conditions at room temperature. In summary, the simple design and preparation route of the zwitterionic polymer/liquid crystal composite film with programming shape-morphing behavior and mild condition-responsive self-healing performance look promising for the fabrication and practical application of novel photo-driven devices and soft robotics.

Appropriate materials collaborated with reasonable structure can significantly increase the separator performance for lithium-ion batteries. In this work, taking the advantages of microfibrous and nanofibrous membranes and compensating for their defects, we developed a composited separator (GOPPH) with excellent overall performance by first wetting-modifying the polyethylene terephthalate microfibers and then laminating a polyvinylidene fluoride-hexafluoropropylene nanofiber layer. Such a combination not only offers the GOPPH separator, from the perspective of structure, with high porosity and hierarchical structure in terms of fiber diameter and pore size, but also provides satisfactory features including wettability, mechanical strength and thermal shutdown function that benefit from the selected materials. Meanwhile, as determined by experimental and theoretical approaches, the obtained GOPPH separator exhibits considerably enhanced lithium ion transport ability with a high lithium ion transference number and transport rate, which thereby endowing the cell with superior cycling stability with a capacity retention of 93% after 200 cycles at 1 C. Therefore, considering battery safety and performance, the GOPPH fibrous membrane could be a promising separator candidate for lithium-ion batteries.

Suppressing the chain transfer reactions during polymerization in late-transition metal-catalyzed olefin polymerization systems is the key to obtaining high molecular weight polyolefin materials. In this work, two efficient strategies (“sandwich” and rotation-restricted strategies) to retard chain transfer reactions in ethylene (co)polymerization were employed for the iminopyridyl system. Herein, a family of iminopyridyl Ni(II) and Pd(II) complexes with a flexible backbone and rigid axial bulky aryl substituents were designed, synthesized and characterized. In ethylene polymerization, the iminopyridyl Ni(II) and Pd(II) catalysts using the two strategies exhibited reasonable activities and generated highly branched polyethylenes with high molecular weights, where catalysts with dibenzosuberyl substituents exhibited significantly higher activities and produced higher molecular weight polyethylene than catalysts with 8-arylnaphthalenyl substituent. A similar trend of activities and molecular weights was also found in the copolymerization of ethylene with MA using the Pd(II) catalysts. Moreover, highly branched E-MA copolymers with moderate to high molecular weights and high incorporation ratios (up to 17.4 mol%) were generated with the two Pd(II) catalysts. Most interestingly, as compared with the dibenzhydryl Ni(II) and Pd(II) catalysts, the catalysts using the two strategies exhibited a superior ability to retard the chain transfer reactions and generated polymers and copolymers with 1−2 orders of magnitude higher molecular weights during ethylene (co)polymerization.

Linear and non-linear rheological properties were examined for in-reactor alloy samples composed of isotactic polypropylene (iPP), ethylene-propylene rubber (EPR), and polyethylene (PE). The samples were prepared through two- or three-stage sequential polymerization, where iPP, as the majority, was synthesized in the first stage, and either EPR or PE, as the minority, was synthesized in the second or third stage. Above T_m of both PE and iPP, the linear viscoelasticity shows two relaxation processes, where the fast and slow processes are attributable to the relaxation of the iPP component and that of the EPR/PE domains, respectively. Both the damping behavior upon applying the step-strain measurements and the shear-thinning behavior under the shear-rate sweep measurements are strongly related to the different degrees of non-linearity of the two relaxation processes.

Recently, numerous mechanically robust synthetic hydrogels have been created. However, unlike natural loading-bearing materials such as cartilages and muscles, most hydrogels have inherently contradictory requirements, obstructing the design of hydrogels with characteristics of robustness and rapid self-recoverability. Herein, we present a facile strategy for constructing mechanically robust and rapidly self-recoverable hydrogels. The linear poly(acrylamide-co-itaconic acid) chains crosslink via coordination bonds and minimal chemical crosslinkers to form the hydrogel network. Such design endows the coordination interactions to be asymmetrically distributed. Under deformation, the coordination interactions exhibit a reversible dissociation-and-reorganization property, demonstrating a new mechanism for energy dissipation and stress redistribution. Thus, the hydrogels possess tensile strength up to 12.5 MPa and toughness up to 28.2 MJ/m³. Moreover, the inherent dynamic nature of the coordination bonds imparts these hydrogels with stretch rate- and temperature-dependent mechanical behavior as well as excellent self-recovery performance. The method employed in this study is universal and is applicable to other polymers with load-bearing yet rapid recovery conditions. This study will facilitate diverse applications of most metallosupramolecular hydrogels.

Because of its softness, wear resistance, biocompatibility, extremely comfortable human touch, thermoplastic vulcanizate (TPV) comprised of silicone rubber (SiR) and thermoplastic polyurethane (TPU) (SiR/TPU TPV) is especially suitable for wearable intelligent devices. Nevertheless, developing good compatibilizer is still required to prepare high performance SiR/TPU TPV. In this study, three kinds of polyurethane-polysiloxane copolymer (PU-co-PSi) with different contents of polysiloxane segment were selected, and their compatibilization effect on SiR/TPU blends was studied using nanomechanical mapping technique of AFM. The results show that using PU-co-PSi with the highest content of polysiloxane segment (PU-co-HPSi), the interface thickness largely increases, and the average size of SiR dispersed phase largely decreases, indicating its good compatibilization effect. By using PU-co-HPSi as compatibilizer, SiR/TPU TPV with a fine SiR dispersed phase and good mechanical performance were successfully prepared. The mechanism on the compatibilization effect of these PU-co-PSi on SiR/TPU TPVs was revealed.

To impart polymers with high electrical conductivity and satisfactory electromagnetic interference shielding efficiency, it is crucial to efficiently construct interconnecting networks of conductive nanofillers in polymer matrices. Herein, on the basis of the three-dimensional (3D) skeleton and volume-exclusion effect of silane-modified tetra-needle ZnO (ST-ZnO) whiskers and the high conductivity of two-dimensional MXene nanosheets, multifunctional MXene/ST-ZnO/waterborne polyurethane (MTW) nanocomposite films are fabricated by coating of MXene on ST-ZnO followed by compounding with waterborne polyurethane. The 3D four-needles of the whiskers facilitate the formation of an interconnecting network in the waterborne polyurethane matrix, while the coating of MXene efficiently makes the interconnecting network of the whiskers conductive at a low amount of the MXene. The resultant MTW ternary nanocomposite film exhibits not only a high electrical conductivity of 4.8×10⁴ S/m, but also an excellent electromagnetic interference shielding effectiveness of over 70 dB in the X-band at a low thickness of 100 μm. In addition, the ternary film also exhibits outstanding Joule heating performances with an equilibrium temperature of 113 °C at a low driving voltage of 3 V. The multifunctional nanocomposite films are promising for applications in portable and wearable electronics and flexible electromagnetic interference shielding devices.

A series of brominated polynorbornene derivatives, including bulky steric hydrophobic groups and highly physical and chemical stable backbones, were synthesized via ring-opening metathesis polymerization and post-functionalized with trimethylammonium (QA), N-methylimidazole (Im), N-methylpyrrolidinium (Pyr) or N-methylpiperidinium (Pip) to construct the entire anion exchange membranes (AEMs). Benefited from prominent phase-separated morphology, PBO-x%-y (x=66, 68, 70; y=QA, Im, Pyr, Pip) AEMs with ion exchange capacity (IEC) approaching 2.0 meq·g⁻¹ exhibited super high hydroxide conductivities. Thereinto, PBO-70%-Pip possessed the highest hydroxide conductivity of 137.3 mS·cm⁻¹ at 80 °C. Moreover, all membranes exhibit low swelling ratio (SR) (the SR of PBO-66%-QA was just 8.6% at 80 °C). That is, bulky steric hydrophobic groups play a crucial role in balancing the high hydroxide conductivity and low SR in AEMs. Furthermore, three AEMs (PBO-66%-QA, PBO-68%-Pyr, PBO-70%-Pip) showed good alkaline stability after immersion into 1.0 mol/L NaOH aqueous solution at 80 °C for 480 h without any degradation.

Modified polyimides (MPIs) show great potential towards 5G communication applications, due to its excellent thermal stability, mechanical property and chemical stability as compared to most of polymers. Introducing fluoride groups or porous structure is favorable to ultra-low dielectric constant (D_k) and dielectric loss (D_f). However, the cost of the fluorinated MPIs is high and their synthetic processes are complicated, and porous MPIs suffer poor mechanical properties. Also, increasing the fraction of free volume is a very effective way to lower D_k through introducing more ultra-low-D_k air component. However, most of this kind of MPIs lag far behind the fluorinated MPIs and the porous MPIs in terms of ultra-low D_f, hindering the application of MPIs in high-speed communication devices. Thus, it is highly desirable to develop intrinsic ultra-low-D_k/D_f MPIs at high frequency with less fluoric groups and nonporous structure. Herein, we introduce a facile and effective strategy to lower D_k and D_f through introducing rigid and large sterically hindered aromatic groups into MPIs. On the one hand, their large steric hindrance effect leads to low D_k by increasing intrinsic free volume. On the other hand, the resulting highly stiff polymer chain and strong intermolecular interaction are favorable to reduce D_f by inhibiting dipole orientations. Based on this strategy, the spirobifluorene groups are preferred. The as-prepared MPIs show excellent dielectric performance with low D_k of 2.74–2.76 and low D_f of 0.00599 at 10 GHz, to some extent, exceeding the multiple fluorinated MPI with D_k/D_f of 2.67/0.00663 at 10 GHz.

Self-healing anticorrosive coatings in extreme environment have attracted considerable interest from researchers. In this work, 4-tert-butylpyridine (TBP) was incorporated into brominated butyl rubber (BIIR) polymer networks to form a reversible ionic bond with the highly reactive bromine anion. Based on the low glass transition temperature of the BIIR polymer and the electrostatic effects, a robust self-healing anticorrosive coating of TBP-BIIR was prepared. TBP-BIIR coating showed a maximum protection efficiency (PE) of more than 94% (TBP-BIIR-acid, 94.37%; TBP-BIIR-alkali, 94.95%; TBP-BIIR-salt, 95.49%) when treated with a strong acid (HNO₃, pH=2), strong base (NaOH, pH=12) and high salt solution (3.5 wt% NaCl). In addition, the PE of coating repaired exceed 89%, and the maximum PE value was approximately 95% in different solutions, which demonstrated its extinguished self-healing abilities. These results indicated that the TBP-BIIR anticorrosive coating could provide excellent safety and durability in special environment, which would be extremely beneficial to improve the working life of metal parts used in aviation and shipping, oil and gas and related industries.

Sizing treatment has shown great potential in improving the interfacial properties of poly(p-phenylene benzodioxazole) (PBO) fiber-reinforced composites, but is severely limited due to the use of flammable and explosive organic solvents. Herein, a new high-efficiency waterborne sizing agent has been developed by using functionalized carbon nanospheres (CNSs) as a nano-reinforcement. Due to abundant oxygen-containing groups, the CNSs greatly improves the surface activity, wettability, and roughness of the PBO fibers. As a result, the interfacial shear strength of the CNSs sized fiber-reinforced composite increases by 79.6% compared with that of the pristine fiber-reinforced composite. Moreover, the excellent mechanical and thermal properties of the PBO fibers remain almost unchanged after sizing treatment. Thus, this work provides an environmentally friendly and scalable method for constructing a strong interface between the PBO fibers and the matrix resins, which makes sense in promoting the application of PBO fiber-reinforced composites in aerospace and military industries.

The dynamic behavior of entangled poly(methyl methacrylate) (PMMA) chains in both the traditional monocationic ionic liquid (MIL) and synthetic dicationic ionic liquid (DIL) with the same anion bis[(trifluoromethyl)sulfonyl]imide ([TFSI]⁻) has been examined over the wide composition range using differential scanning calorimetry and rheological measurements. PMMA/DIL and PMMA/MIL systems exhibit two glass transitions in the midrange of composition due to self-concentration effects. PMMA in DIL shows slower relaxation behavior, however, after the iso-free-volume correction, the terminal relaxation time τ₀ of PMMA in both the DIL and MIL presents the power law behavior τ₀~ϕ^v with exponent v conforming to experimental results for conventional polymer solutions (v=2.0±0.2). At high ILs concentration (70%), the entanglement molecular weight M_e of PMMA/DIL system is lower than that of PMMA/MIL system owing to the formation of additional physical network in DIL, while the difference of M_e is reversed at low ILs content. The composition dependence might be related to the fact that the probability of formation of physical cross-linking points in linked double imidazolium ring increases with the increase of DIL content. The recovered creep strain of PMMA/DIL is almost 18 times of PMMA/MIL, exhibiting significantly better viscoelastic behavior.