The backbones of polymers are generally composed of non-metal elements such as C, N, O and Si. Here we propose and synthesize a new class of polymers whose backbones are completely made from metal atoms connected by chemical bonds, and they are thus named metal-backboned polymers. As a demonstration, nickel is selected as the metal to construct the nickel-backboned polymers with varied lengths, which are verified by mass spectrometry and studied by ultraviolet-visible spectroscopy. These metal-bonded polymers open up a new avenue to develop functional polymers in the future.

Theory of polymer crystallization is listed as one of the top ten current challenges in polymer community. Clarifying the uniqueness of polymer crystallization should be the first step to search for the roadmap for targeting this challenge. Chain flexibility and connectivity are two peculiar characteristics of polymers, which differentiate their dynamics and structures from that of small molecules. The uniqueness of polymer crystallization must also stem from these two peculiar characteristics, which, however, has not been attracted significant attention. A local structure order may be essential in assisting the transformation of flexible chain to rigid segment with conformational ordering. The entanglement pressure and entanglement free energy may help to understand how entanglement affect nucleation in polymer network and why the interlamellar amorphous layer always accompany the formation of crystal layer. Some recommendations will be given for future study.

Poly(glycolic acid) is a biocompatible as well as biocomposable polymer with superior mechanical and barrier properties and, consequently, has found important applications in both medical and packaging fields. However, the high hydrolysis rate in a high humidity environment restricts its application. In this work, a solid-state drawing process after melt extrusion is applied in order to produce fibrous PGA with enhanced mechanical properties and a much better resistance towards hydrolysis. The crystal structure of PGA gradually transformed from spherulites into oriented fibrous crystals in the stretching direction upon solid-state drawing. Meanwhile, both the length of microfibril and the size of lamellae increased initially with the drawing ratio (DR), while the chain-folded lamellae transformed into extended-chain fibrils at high(er) DR. The oriented structures lead to an overall improvement of the mechanical properties of PGA, e.g., the tensile strength increased from 62.0±1.4 MPa to 910±54 MPa and the elongation at break increased from around 7% to 50%. Meanwhile, the heat capacity of totally mobile amorphous PGA (ΔC_p⁰=0.64 J∙g⁻¹∙°C⁻¹) was reported for the first time, which was used to analyze the content of mobile amorphous fraction (X_MAF) and rigid amorphous fraction (X_RAF). Both the oriented chain-folded lamellae crystals and the tightly arranged RAF are beneficial to prevent water molecules from penetrating the matrix, thus improving the resistance towards hydrolysis. As a consequence, the fibrous PGA with a DR of 5 showed a tensile strength retention rate of 17.3% higher in comparison with the undrawn sample after 7-days accelerated hydrolysis. Therefore, this work provides a feasible method to improve the mechanical and resistance towards hydrolysis performance of PGA, which may broaden its application and prolong the shelf-life of PGA products.

A series of polypeptoids with dual photo/thermo-responsiveness were prepared by incorporating both azobenzene (Azo) group and oligo(ethylene glycol) (OEG) segment into the side chains. Firstly, the N-substituted-N-carboxyanhydride (NNCA) monomers with different Azo and OEG groups were synthesized, and then a single NNCA ring-openning polymerization was performed to afford dual-responsive polypeptoids without any post-polymerization modification. The ultra-violet/visible (UV/Vis) photo-responsive behaviors of the polypeptoids were achieved by cis-trans photoisomerization of the Azo group and confirmed by both ¹H-NMR and UV/Vis spectroscopy. The thermo-responsive behaviors were realized by both OEG segment and Azo group and confirmed by UV/Vis spectroscopy and dynamic light scattering. This work demonstrated the synthetic pathway for dual responsive polypeptoids using NNCA monomers with two responsive groups and revealed the potential of polypeptoids as smart materials that could respond to different environmental stimuli.

The existence of tumor immunosuppressive microenvironment (TIME) is the major determinant for the poor efficacy of current tumor immunotherapy. Tumor-associated macrophages (TAMs) tend to become tumor-promoting M2-like phenotype and hinder immune response in solid tumors. Repolarization of TAMs from M2 to anti-tumor M1 phenotype is robust for remodeling the TIME. Herein, we developed a redox-responsive nanogel as the delivery system of Toll-like receptor 7 and 8 (TLR7/8) agonist (R848) prodrug for potent cancer immunotherapy. The nanogel (denoted as R848-Gel) was obtained by emulsion polymerization of HSEMA and R848 prodrug (R848-HSEMA), whose size was appropriate 100 nm. R848-Gel could be internalized by macrophages and dendritic cells in vitro, and effectively repolarized M2 into M1 macrophages and promoted the maturation of antigen-presenting cells. In vivo study indicated that the R848-Gel showed a stronger tumor inhibitory effect and no drastic body weight change compared with free drug. Immune cell analysis after the treatment indicated that R848-Gel was helpful to activating the TIME. In summary, this study provides a simple but effective vehicle for R848 to improve cancer immunotherapy.

The dense networks of conventional hydrogel hinder the efficient cell penetration and thus tissue regeneration. In this study, a macroporous cryogel with excellent mechanical properties was designed and fabricated through cryogelation and crosslinking of methacrylated gelatin (Gel-MA) and gelatin grafted with 2-ureido-4[1H]-6-methyl-pyrimidinone (Gel-UPY). The successful modification of the two functional units on the side chain of gelatin was confirmed by ¹H-NMR and infrared spectroscopy. The macroporous structure of cryogel was verified by scanning electron microscopy and confocal microscopy. The compressive modulus of cryogel (110 kPa) was 2 magnitudes higher than that of the conventional hydrogel of the same chemical compositions (8 kPa). Both the hydrogel and cryogel exhibited excellent stress-recovery ability. The cryogel could well maintain the viability of chondrocytes and facilitated their migration into the scaffold interior. After being implanted into osteochondral defects in rabbits for 12 w, the Gel-MA/Gel-UPY cryogel better facilitated the regeneration of upper cartilage and subchondral bone compared to the conventional hydrogel.

Bioprosthetic heart valves (BHVs) are important for transcatheter valve replacement. Current commercial BHVs on the market are basically porcine or bovine pericardium (BP) crosslinked with glutaraldehyde (GA). Simply applying GA to BHVs can enhance mechanical stability, but cannot alleviate in vivo calcification. In this work, we developed a two-step decellularization (TSD) strategy to modify this biomacromolecular network, in which BP was post-treated, as the second step of decellularization, with a mild biosurfactant n-dodecyl-β-D-maltoside in a mixture of isopropanol and phosphate-buffered saline after the first step of traditional decellularization and GA cross-linking. The TSD-treated BP exhibited not only low cytotoxicity and excellent mechanical properties in vitro, but also low immune responses and significant anticalcification in vivo. After 60 days of subcutaneous implantation in the back of Wistar rats, the calcium content was, as quantified with an inductively coupled plasma optical emission spectrometer, only 1.1 μg/mg compared to 138.6 μg/mg in the control group without the post-treatment. In addition, collagen fibrils were observed with field emitting scanning electron microscopy (SEM), and the morphology and composition of the calcified sites resulting from in vivo biomineralization were studied with SEM with energy dispersive spectroscopy and also X-ray diffraction. This study proposes a facile yet effective anticalcification strategy for the modification of the bovine pericardial bioprosthetic heart valve, a natural biomacromolecular network.

In this study, we investigate the effect of the exposure dose on the mechanical property of the photoresins generated with acrylate self-polymerization and thiol-ene polymerization. The results indicate that the mechanical performance of the thiol-ene photoresin is highly depended on the exposure dose during the solidification process. With 350-fold exposure dose change, the stiffness of the thiol-ene photoresin reached more that 700-fold change compare to 14-fold of the acrylate photoresin. We developed a TPL photoresist based on our results and show the capability to fabricate microstrucutres with high resolution and variable mechanical performances using this method.

According to the Kamlet-Abraham-Taft (KAT) polarity parameters (α, β, π^*), polymers and solvents can be categorized as hydrogen-bond (H-bond) acidic (α>β) or H-bond basic (α<β). Recently, we proposed a quantitative hydrogen bonding (QHB) analysis to predict the solubility of polymers in ionic liquids (ILs) using the product of ΔαΔβ<0 as an indicator, where Δα is the difference between the H-bond acidic parameters of the polymer and IL, and Δβ is the difference in their basicity, while the prerequisite of the “complementary” principle (i.e., that one component is H-bond acidic and the other is basic) is satisfied. Here, the applicability of QHB analysis was first confirmed by testing the solubilities of carefully chosen polymer/deep eutectic solvent (DES) pairs, as the DESs were eutectic mixtures dominated by hydrogen bonding interactions. Then, our attention focused on the solubility of cellulose in DESs. Our testing results as well as the typical published results were summarized, which indicate that the potential DESs for cellulose dissolution and regeneration must be of the H-bond basic type because the “complementary” principle should be satisfied as a prerequisite. However, the H-bond basic DESs investigated in this study do not show the superior solubility of cellulose that has been commonly observed for H-bond basic ILs, even if the criterion of ΔαΔβ<0 is satisfied for both DESs and ILs. Possible reasons for this discrepancy are given to understand the varying effectiveness in cellulose dissolution for H-bond basic DESs and ILs.

Liquid trimethoxy silane-functionalized cis-polybutadiene (cis-PB-Si(OMe)₃), possessing number-average molecular weights of cis-PB segments (M_n,PB) ranging from 1800 g/mol to 5400 g/mol, with cis-1,4 content of ca. 80% and high functionality (>96%) could be synthesized by coordination copolymerization of livingcis-PB chain ends with ethenyltrimethoxy-silane with neodymium-based catalytic system. The silicon hydroxyl-functionalized cis-polybutadiene (cis-PB-Si(OH)₃)-based micelles in water have been achieved by in situ hydrolysis of cis-PB-Si(OMe)₃ in hexane/water mixture (pH=6.8) at 70 °C and by sequential removal of residue hexane. The size of the above micelles with soft elasticcis-PB cores could be remarkably enlarged by loading SiO₂ nanoparticles on their surfaces via hydrogen bonding interaction. Giant supramolecular long chain aggregates or networks formed by hydrogen bonding interaction and possible O―Si―O chemical bonds between cis-PB-Si(OH)₃-based micellar surfaces had relatively large size and thus precipitated from water after several months of storage, leading to production of cis-PB-Si(OH)₃ solid elastomer with extremely low T_g at −107.0 °C. The left cis-PB-Si(OH)₃-based micelles in water with relatively small size gradually formed the water-insoluble cis-PB-Si(OH)₃-based supramolecular aggregates or networks. The cis-PB-Si(OH)₃-based supramolecular elastomer exhibited excellent self-healing property within 60 s at 25 °C. The elastomer (20 mg) in a joint of 25 mm × 30 mm (2.7 mg/cm²) provided very strong adhesion for two pieces of glass and the bound glass keep unchanged at room temperature for 98 h even hung with 100 g of steel column below. The cis-PB-Si(OH)₃-based supramolecular elastomer would have potential applications in adhesives, self-healing materials, damping materials and elastic materials.

To construct structurally stable sulfur cathode of Li-S battery with improved cycling performance, poly(acrylic acid) (PAA) crosslinked by cationic hydroxypropyl polyrotaxane (HPRN⁺) via dynamically reversible boronic ester bonds is synthesized and serves as the cathode binder. The smart polymer networks offer multifunction including buffering the volume change of the cathode during charge/discharge through the pulley effect of polyrotaxanes (PR), suppressing the shuttle effect by adsorption of polysulfide using the plentiful carboxyl, hydroxyl and quaternary ammonium cationic groups, and self-healing the micro-damages to ensure stable conduction pathways of the electrode. As a result, the Li-S batteries based on this novel multifunctional binder and simple commercial sulfur/carbon composites cathode exhibit excellent specific capacity and cycling stability. In particular, the specific capacity decay per cycle of the cell is only 0.064% along with high Coulombic efficiency after 550 cycles at 1.0 C, which is superior to most of the reported binders. Even under high sulfur loading, moreover, the cathode can deliver superior areal capacity and cycling stability. This proposed binder provides a new way for the design of high-stability sulfur cathodes.

The development of n-type polymer thermoelectrics lags far behind that of p-type ones in view of material diversity and performance. New structural insights into the thermoelectric performance are needed for efficient n-type polymer thermoelectric materials. Herein, we developed three acceptor-acceptor type organoboron polymers and investigated the effect of backbone configuration on thermoelectric performance. The three polymers are designed based on double B←N bridged bipyridine (BNBP) unit with monomeric thieno[3,4-c]pyrrole-4,6-dione (TPD), TPD dimer and TPD trimer as the copolymerizing units, respectively. The three polymers show similar low LUMO energy levels but different backbone configuration. Compared with the wavy backbone configuration, the pseudo-straight backbone configuration imparts the polymer with much enhanced crystallinity and electron mobility. As a result, after n-doping, the polymer with pseudo-straight configuration shows much higher electronic conductivity and power factor. We think these findings could serve as important guidelines for molecular design toward efficient n-type polymer thermoelectric materials.

The key to improve the foam’s performance is to optimize the cellular structure and its bulk-material composition. Here, the hyperbranched polymer modified fluorinated multi-walled carbon nanotube (HPMCNT-F) based on the nucleophilic reactions of MCNT-F was successfully prepared and used to composite with PI foams. The pristine MCNT shows a poor dispersity and weak interfacial interaction with PI matrix. While HPMCNT-F exhibits an excellent dispersity and effectively forms covalent/non-covalent interaction with PI matrix due to the surface-structure engineering, resulting in the enhancement of the PI bulk. Furthermore, HPMCNT-F works as a heterogeneous nucleation agent in PI foam to optimize the cellular structure. The enhancement of PI bulk and the optimizing of cellular structure result in the increase of compressive special strength of composite foam by 58.9% with a low loading of 1.6 wt% HPMCNT-F. Moreover, the hyperbranched polymers effectively prevent the thermal conduction among HPMCNT-F, and the isolated MCNTs effectively block thermal radiation through absorption and reflection the infrared waves. Thus, the thermal conductivity was reduced by 8.0% simultaneously.

Conventional fluorescent polymers are featured by large conjugation structures. In contrast, a new class of fluorescent polymers without any conjugations is gaining great interest in immerging applications. Polyamide is a typical member of the conjugation-free fluorescent polymers. However, studies on their electrophotonic property are hardly available, although widely used in many fields. Herein, poly(ethylene succinamide), PA24, is synthesized; its chemical structure confirmed through multiple techniques (NMR, FTIR, XRD, etc.). PA24 is highly emissive as solid and in its solution at room temperature, and the emission is excitation and concentration dependant, with an unusual blue shift under excitation from 270 nm to 320 nm, a hardly observed phenomenon for all fluorescent polymers. Quite similar emission behavior is also observed under cryogenic condition at 77 K. Its emission behavior is thoroughly studied; the ephemeral emission blue-shift is interpreted through Förster resonance energy transfer. Based on its structures, the emission mechanism is ascribed to cluster-triggered emission, elucidated from multi-analyses (NMR, FTIR, UV absorbance and DLS). In presence of a dozen of competitive metal ions, PA24 emission at 450 nm is selectively quenched by Fe³⁺. PA24 is used as probe for Fe³⁺ and H₂O₂ detections and in data encryption. Therefore, this work provides a novel face of polyamide with great potential applications as sensors in different fields.

Poly(lactic acid) (PLA) is a promising bio-based environmentally-friendly plastic. Nevertheless, the physical aging-induced brittleness of PLA limits its widespread applications. Blending with immiscible ductile polymer is an effective way to toughen PLA. However, the underlying details of the toughening mechanism and, in particular, the effect of physical aging are not well understood. Herein, atomic force microscopy (AFM) based nanomechanical mapping technology was utilized to visualize the differences in the deformation mechanisms between unaged and aged PLA/poly(ε-caprolactone) (PCL) blend upon uniaxial drawing. Results show that physical aging has a significant effect on the microscopic Young’s modulus and its distribution of PLA matrix, resulting in a highly heterogeneous response of the PLA/PCL blend to external stress and affecting the mechanical properties of the PLA phase under different extensions. This work provides a new experimental basis for understanding the effect of physical aging on the mechanical properties of PLA-based materials.

To illustrate mechanisms of Payne effect in rubbers and their nanocomposites experiencing large amplitude oscillatory shear (LAOS), comparison studies were performed in styrene-isoprene-styrene (SIS) copolymers and their selectively crosslinked materials at temperatures below and above glass transition temperature of the polystyrene (PS) phase. It was found that under periodic dynamic shear, the strain softening is reversible when the polyisoprene (PI) phase, either crosslinked or not, is restricted by hard PS domains but it shows hysteresis once the PS domains disassociate. The strain softening can happen at the time scale of intrinsic Rouse relaxation of elastically active network strands. Critical stress of strain softening scales with number density of elastically active network strands, a simple relation being verified not only in the selectively crosslinked SIS copolymers but also in PI gum vulcanizates and carbon black filled PI compounds. Payne effect is traditionally used to term strain softening of highly filled rubber vulcanizates under LAOS deformation while evidenced herein is that the Payne effect of highly filled rubber vulcanizates shares the mechanism being common to the strain softening of SIS copolymers.

In this work, the nanostructures and phase diagrams of lamella-forming and cylinder-forming ABC linear triblock copolymers confined in spherical cavities are investigated on the basis of real-space self-consistent field theory. We designate specific monomer-monomer interactions and block composition and study morphology transformation under spherical confinement with a neutral surface. Various potentially valuable morphological structures, such as two- or three-colored spheres, rotational structures, and biconcave disklike structures, are identified in the phase diagrams constructed on confining diameters. Single confinement induces an obvious transformation of self-assembled structures, which still retain some of the conformational properties of bulk structures. We then focus on phase morphology under preferential surfaces. Absorption can smooth out differences in block ratios, and similar structures can be assembled from block copolymers with different proportions. We incorporate a non-centrosymmetric feature into our spherical confinement model and design a Janus adsorption field to explore unpredictable microphase behavior. Results show that the unbalance of the block ratio causes adsorption to exert a stable shaping effect on conformation. The influence of confinement on the degree of freedom of polymer chains disrupts the influence of adsorption on the complexity and transformation activity of self-assembled structures. The theoretical results correspond to recent experimental observations and contribute to the field functional material synthesis.