To design high efficiency polymer solar cells (PSCs), it is of great importance to develop suitable polymer donors that work well with the low bandgap acceptors, providing complementary absorption, forming interpenetrating networks in the active layers and minimizing energy loss. Recently, we developed a series of two-dimension-conjugated polymers based on bithienylbenzodithiophene-alt-benzotriazole backbone bearing different conjugated side chains, generally called J-series polymers. They are medium energy bandgap (E_g) polymers (E_g of ca. 1.80 eV) with strong absorptions in the range of 400−650 nm, and exhibit ordered crystalline structures, high hole mobilities, and more interestingly, tunable energy levels depending on the structure variations. In this feature article, we highlight our recent efforts on the design and synthesis of those J-series polymer donors, including an introduction on the polymer design strategy and emphasis on the crucial function of differential conjugated side chain. Finally, the future opportunities and challenges of the J-series polymers in PSCs are discussed.

Surface design and engineering is a critical tool to improve the interaction of materials with their surroundings. Immobilization of soft hydrogels is one of the attractive strategies to achieve surface modification. The goal of this review is to provide a comprehensive overview of the different strategies used for surface tethering of hydrogel layers via crosslinking immobilization of pre-fabricated functional polymers. In this strategy, crosslinkable polymers are first prepared via various polymerization techniques or post-functionalization of polymers. Afterwards, the crosslinkable polymers are attached or tethered on the surfaces of substrates using a variety of approaches including photo-crosslinking, click reactions, reversible linkages, etc. For each case, the principles of hydrogel tethering have been explained in detail with representative examples. Moreover, the potential applications of the as-modified substrates in specific cases have also been addressed and overviewed.

A near-infrared non-fullerene acceptor (NFA) BDTIC, based on thienopyrrole-expanded benzo[1,2-b:4,5-b′]dithiophene unit (heptacyclic S,N-heteroacene) as core, is designed and synthesized. The aromatic pyrrole ring with strong electron-donating ability in the core enhances the intramolecular charge transfer effect, finely tunes the optical bandgap and absorption profile of BDTIC, and thus results in a narrowed optical bandgap ($E_{\rm{g}}^{\rm{opt}}$) of 1.38 eV and a near-infrared absorption to 900 nm. When BDTIC is paired with donor polymer PBDB-T to fabricate organic solar cells, the optimized device achieves a best power conversion efficiency of 12.1% with a short-circuit current density of 20.0 mA·cm^–2 and an open-circuit voltage of 0.88 V. The photovoltaic performance benefits from the broad absorption, weak bimolecular recombination, efficient charge separation and collection, and favorable blend morphology. This work demonstrates that thienopyrrole-expanded benzo[1,2-b:4,5-b′]dithiophene unit (heptacyclic S,N-heteroacene) is a promising building unit to construct high-performance NFAs by enhancing the intramolecular charge transfer effect, broadening absorption as well as maintaining good intermolecular stacking property.

Side-chain engineering plays a significant role in the design of conjugated materials. In this work, a series of conjugated polymers PBDB-T-R with functionalized groups at the end of side units were developed as electron donor for organic solar cells (OSCs). The donor polymers PBDB-T-I and PBDB-T-OAc with iodine and acetate end groups exhibited similar absorption and energy levels, but showed much improved PCEs in OSCs compared to the polymer PBDB-T-H without substitutions at the end groups. Additionally, we found that PBDB-T-I and PBDB-T-OAc based cells exhibited optimized performance when using chloroform as solution-processed solvent without any additives. These results indicate that these conjugated polymers can act as self-additive to fabricate photoactive layers via solution process in OSCs.

Green monomers, such as carbon dioxide (CO₂), are closely related to our daily life and highly desirable to be transferred to functional polymers with diverse structures and versatile properties because they are abundant, cheap, nontoxic, renewable, and sustainable. However, the polymerizations based on these green monomers are to be further developed. In this work, a facile CO₂ and alkyne-based one-pot, two-step, four-component tandem polymerization was successfully established. The polymerization of CO₂, diynes, alkyl dihalides, and primary/secondary amines can proceed under mild reaction conditions and regio- and stereoregular poly(aminoacrylate)s with good solubility and thermal stability were obtained in high yields (up to 95%). Notably, distinctly different stereoregularity of resultant poly(aminoacrylate)s was realized via using primary or secondary amines. Using the former would readily generate polymers with 100% Z-isomers, whereas the latter furnished products with over 95% E-isomers. Through different monomer combination, the polymers with tunable structures and properties were obtained. Moreover, the tetraphenylethene units containing poly(aminoacrylate)s, showing the unique aggregation-induced emission characteristics, could function as a fluorescent probe for sensitive explosive detection. Thus, this work not only develops a facile CO₂ and alkyne-based multicomponent tandem polymerization but also provides a valuable strategy to fine-tune the polymer structures and properties, which could be potentially applied in diverse areas.

The controlled and efficient synthesis of polymers with tailored topologies is challenging but important for exploring structure/property research. Herein, we proposed a concept of macro-latent monomer to achieve the controlled growth of polymer topologies. The macro-latent monomer was installed by a dynamic furan/maleimide covalent bond at the chain terminal. One-shot reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene and the macro-latent monomer created controlled growth of polymer topologies. Low temperature such as 40 °C could not activate the macro-latent monomer and thus the polymerization created the homo-polystyrene. By contrast, high temperature of ~110 °C activated the macro-latent monomer, and a maleimide-terminated macro-monomer was released via the retro-Diels Alder reaction. This macro-monomer immediately joined the cross polymerization with styrene and thus produced the side chains. By delicately manipulating the polymerization temperature, the predetermined placement of the macro-latent monomer-derived polymeric side-chains created controllably growing topologies, including star-, π-shaped, and density-variable grafting copolymers. This work paved a new way for creating on-demand topologies and would greatly enrich the topology synthesis.

The catalytic activity and stereospecificity of olefin polymerization by using heterogeneous TiCl₄/MgCl₂ Ziegler-Natta (Z-N) catalysts are determined by the structure and nature of active centers, which are mysterious and fairly controversial. In this work, the propylene polymerization kinetics under different polymerization temperatures by using Z-N catalysts were investigated through monitoring the concentration of active centers [C*] with different tacticity. SEM was applied to characterize the catalyst morphologies and growing polypropylene (PP) particles. The lamellar thickness and crystallizability of PP obtained under different polymerization conditions were analyzed by DSC and SAXS. The PP fractions and active centers with different tacticity were obtained with solvent extraction fractionation method. The catalytic activity, active centers with different tacticity and propagation rate constant k_p, fragmentation of the catalyst, crystalline structure of PP are correlated with temperature and time for propylene polymerizations. The polymerization temperature and time show complex influences on the propylene polymerization. The higher polymerization temperature (60 °C) resulted higher activity, k_p and lower [C*], and the isotactic active centers C_i* as the majority ones producing the highest isotactic polypropylene (iPP) components showed much higher k_p when compared with the active centers with lower stereoselectivity. Appropriate polymerization time provided full fragmentation of the catalyst and minimum diffusion limitation. This work aims to elucidate the formation and evolution of active centers with different tacticity under different polymerization temperature and time and its relations with the fragmentation of the PP/catalyst particles, and provide the solutions to the improvement of catalyst activity and isotacticity of PP.

As a widely used reinforcing filler of rubber, carbon black (CB) often enhances the nonlinear Payne effect and its mechanism still remains controversial. We adopt simultaneous measurement of rheological and electrical behaviors for styrene-butadiene rubber (SBR)/CB compounds and CB gel (CBG) during large deformation/recovery to investigate the contribution of conductive CB network evolution to the Payne effect of the compounds. In the highly filled compounds, the frequency dependence of their strain softening behavior is much more remarkable than that of their CB network breakdown during loading, while during unloading the unrecoverable filler network hardly affects the complete recovery of modulus, both revealing that their Payne effect should be dominated by the disentanglement of SBR matrix. Furthermore, the bound rubber adjacent to CB particles can accelerate the reconstruction of continuous CB network and improve the reversibility of Payne effect. This may provide new insights into the effect of filler network, bound rubber, and free rubber on the Payne effect of CB filled SBR compounds.

The isotactic polypropylene (iPP) usually shows a unique parent-daughter lamellae structure in which the parent and daughter lamellae are against each other with a near perpendicular angle (80° or 100°). Inducing a high fraction of oriented cross-hatched structure in iPP during processing is desirable for designing the bi-oriented iPP products. We processed a commercial iPP via tensile-stretching and die-drawing to evaluate the structural evolution of oriented parent-daughter lamellae. It turned out that the die-drawing process had an advantage in attaining a high fraction of oriented cross-hatched structure of iPP, as compared to the free tensile stretching. Besides, the presence of α-nucleating agents affected the formation of oriented parent-daughter lamellae in the die-drawn samples whereas such influence diminished in the free stretched ones. It was found that the confined deformation inside the die led to the well-preserved oriented cross-hatched structure in the die-drawn iPP.

The structural evolutions of LLDPE-LMW/HMW blend during uniaxial deformation at temperatures of 80 and 120 °C were investigated by the in situ synchrotron radiation small- and wide-angle X-ray scattering (SR-SAXS/WAXS). The magic sandwich echo (MSE) sequence was used to detect a virtually dead-time-free induction decay (FID) for solid-state NMR analysis. The thermal property of the blend was first checked by DSC, and the temperature dependence of the overall crystallinity was obtained by MSE-FID. The onset melting temperature is determined to be 116 °C (DSC), and the enhanced π-flip motions in the crystalline domains are clearly observed at T>60 °C by MSE-FID. For deformation at 80 °C, the lamellae become staggered in the strain-softening region as shown by the four-point SAXS pattern, whereas further deformation leads to the melting-recrystallization in the strain-hardening region. For deformation at 120 °C, the six-point SR-SAXS signal appears just after the four-point SR-SAXS signal, which indicates the formation of new lamellae along deformation direction. In addition, no phase transition occurs in the whole deformation process at both temperatures. Current work shows the detailed temperature dependence microstructural evolution of LLDPE-LMW/HMW blend. This is expected to provide more structural information for correlating microscopic structure with macroscopic mechanical performance.

The branching structures in natural rubber (NR) were believed to be critical for its superior mechanical properties. However, it is challenging to unravel the branching structure-function relationship of NR due to the complexity of the system. Herein, polyisoprene-(polyisoprene-g-polylactide) (PI-PLA) as model compound containing branching structure was designed and synthesized, which can improve the modulus, strength and viscoelasticity activation energy compared to those of the pristine polyisoprene (PI). The reason is that the branching structure contributes to the entanglement between polyisoprene chains. In order to probe the effect of branching structure on noncovalently crosslinked system, the polyisoprene block of PI-PLA was epoxidized and mixed with Fe³⁺ ions to introduce coordination bonds. Compared with the linear counterpart, the branching structure obviously enhanced activation energy of coordinated polyisoprenes, remarkably improving the mechanical properies of elastomer.

In this work, hydroxyl-terminated oxalamide compounds N¹,N²-bis(2-hydroxyethyl)oxalamide (OXA1) and N¹,N¹′-(ethane-1,2-diyl)bis(N²-(2-hydroxyethyl)oxalamide (OXA2) were synthesized to initiate the ring-opening polymerization of L-lactide for preparation of oxalamide-hybridized poly(L-lactide) (PLA_OXA), i.e., PLA_OXA1 and PLA_OXA2. The crystallization properties of PLA were improved by the self-assembly of the oxalamide segments in PLA_OXA which served as the initial heterogeneous nuclei. The crystal growth kinetics was studied by Hoffman-Lauritzen theory and it revealed that the nucleation energy barrier of PLA_OXA1 and PLA_OXA2 was lower than that of PLA. Consequently, PLA_OXA could crystallize much faster than PLA, accompanied with a decrease in spherulite size and half-life crystallization time by 74.8% and 86.5% (T=125 °C), respectively. In addition, the final crystallinity of PLA_OXA1 and PLA_OXA2 was 6 and 8 times higher, respectively, in comparison with that of neat PLA under a controlled cooling rate of 10 °C/min. The results demonstrate that the hybridization of oxalamide segments in PLA backbone will serve as the self-heteronucleation for promoting the crystallization rate. The higher the content of oxalamide segments (PLA_OXA2 compared with PLA_OXA1) is, the stronger the promotion effect will be. Therefore, this study may provide a universal approach by hybridizing macromolecular structure to facilitate the crystallization of semi-crystalline polymer materials.