The high fire safety of polymer nanocomposites is being pursued by research institutions around the world. In addition to intrinsic flame retardancy strategy, the additive-type flame retardants have attracted increasing attention due to low commercial cost and easy fabrication craft. However, traditional additive-type flame retardants usually need high addition amount to achieve a desirable effect, which causes many side-effects on the overall performance of polymer materials, such as deteriorated mechanical property and processability. At present, two-dimensional (2D) nanomaterials have also been applied to reduce the fire hazards of polymer (nano)composites with the coupling of barrier function and catalysis as well as carbonization effect. Even though most research work mainly focus on graphene-based flame retardants, more emerging two-dimensional nanomaterials are taking away research attention, due to their complementary and unique properties, mainly including hexagonal boron nitride (h-BN), molybdenum disulfide (MoS₂), metal organic frameworks (MOF), carbon nitride (CN), titanium carbide (MXene) and black phosphorene (BP). In this review, except for graphene, the flame retardant mechanism involving different layered nanomaterials are also reviewed. Meanwhile, the functionalization method and flame retardancy effect of different layered nanomaterials are emphatically discussed for offering an effective reference to solve the fire hazards of polymer materials. Moreover, this work objectively evaluates the practical significance of polymer/layered nanomaterials composites for industrial application.

Injectable hydrogels as an important class of biomaterials have gained much attention in tissue engineering. However, their crosslinking degree is difficult to be controlled after being injected into body. As we all know, the crosslinking degree strongly influences the physicochemical properties of hydrogels. Therefore, developing an injectable hydrogel with tunable crosslinking degree in vivo is important for tissue engineering. Herein, we present a dual crosslinking strategy to prepare injectable hydrogels with step-by-step tunable crosslinking degree using Schiff base reaction and photopolymerization. The developed hyaluronic acid/poly(γ-glutamic acid) (HA/γ-PGA) hydrogels exhibit step-by-step tunable swelling behavior, enzymatic degradation behavior and mechanical properties. Mechanical performance tests show that the storage moduli of HA/γ-PGA hydrogels are all less than 2000 Pa and the compressive moduli are in kilopascal, which have a good match with soft tissue. In addition, NIH 3T3 cells encapsulated in HA/γ-PGA hydrogel exhibit a high cell viability, indicating a good cytocompatibility of HA/γ-PGA hydrogel. Therefore, the developed HA/γ-PGA hydrogel as an injectable biomaterial has a good potential in soft tissue engineering.

The effect of exogenous hydroxyl, carboxyl groups and/or Sn²⁺ on pyrolysis reactions of poly(L-lactide) (PLLA) was investigated by thermogravimetric analysis (TGA). The activation energy (E_a) of pyrolysis reactions was estimated by the Kissinger-Akahira-Sunose method. The kinetic models were also explored by the Malek method, and the random degradation behavior was determined by comparing the plots of $ {{\rm{ln}}}\{-{{\rm{ln}}}[1-{\left(1-w\right)}^{0.5}]\} $ versus 1/T for experimental data from TGA with model reactions. The pyrolysis reaction rate of PLLA was affected slightly by exogenous hydroxyl and carboxyl groups at lower levels of Sn with 65−70 mg·kg⁻¹ but increased appreciably in the presence of extraneous Sn²⁺, ―COOH/Sn²⁺, or ―OH/Sn²⁺. The E_a values for the pyrolysis reactions of the PLLAs that provided lactide were different under the catalysis of Sn²⁺ in different chemical environments because Sn²⁺ can form the new Sn-carboxylate and Sn-alkoxide with exogenous carboxyl and hydroxyl groups, which were different in steric hindrance for the formation of activated complex between Sn²⁺ and PLLA. Under the catalysis of Sn²⁺, a lactide molecule can be directly eliminated selectively at a random position of PLLA molecular chains, and the molecular chain of PLLA cannot change two PLLA fragments at the elimination site of lactide. However, it was regenerated into a new PLLA molecule with the molecular weight reduced by 144 g·mol⁻¹.

The time-resolved attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy is employed to investigate the transport mechanism of gel electrolytes by monitoring the diffusion behavior of propylene carbonate-lithium bis(trifluoromethylsulfonyl)imide (PC-LiTFSI) solution through poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) films. Fickian behavior has been observed for both TFSI⁻ and PC. Higher temperature leads to faster diffusion of TFSI⁻ and PC, which could be related to the increased free volume in P(VDF-HFP) matrix and rapid molecular movements upon heating. Various molecular interactions among LiTFSI, PC and P(VDF-HFP) have been recognized. During the diffusion process, PC molecules, in the form of small clusters, can firstly diffuse through the P(VDF-HFP) film and interact with P(VDF-HFP) by dipole-dipole interaction, acting as the plasticizer. Then, Li⁺ diffuses into P(VDF-HFP) with the help of ion-dipole interactions between Li⁺ and C＝O of PC. Meanwhile, TFSI⁻ diffuses through the polymer matrix in solvation states. In addition, slight ion-dipole interactions between Li⁺ and P(VDF-HFP) have been observed as well. Results in this work contribute to a better understanding of transport process in gel polymer electrolytes for lithium-ion batteries and support the development of improved gel polymer electrolytes by rationally regulating molecular interactions.

For the rational design of metal catalyst in olefin polymerization catalysis, various strategies were applied to suppress the chain transfer by bulking up the axial positions of the metal center, among which the ”sandwich” type turned out to be an efficient category in achieving high molecular weight polyolefin. In the α-diimine system, the “sandwich” type catalysts were built using the typical 8-aryl-naphthyl framework. In this contribution, by introducing the rotationally restrained benzosuberyl substituent into the ortho-position of N-aryl rings, a new class of “sandwich-like” α-diimine nickel catalysts was constructed and fully identified. The rotationally restrained benzosuberyl substituents played a “sandwich-like” function by capping the nickel center from two axial sites. Compared to the nickel catalyst Ni1 bearing freely rotated benzhydryl substituent, Ni2 featuring benzosuberyl substituent enabled the increase (8 times) of polymer molecular weights from 8 kDa to 65 kDa in the polymerization of ethylene. By further increasing the steric bulk of another ortho-site of the N-aryl ring, the polymer molecular weight even reached an ultrahigh level of 833 kDa (M_w=1857 kDa) using the optimized Ni3. Notably, these nickel catalysts could also mediate the copolymerization of ethylene with methyl 10-undecenoate, with Ni3 giving the highest copolymer molecular weight (88 kDa) and the highest incorporation of comonmer (2.0 mol%), along with high activity of up to 10⁵ g·mol⁻¹·h⁻¹.

A series of hydroxyl-terminated polyethylenes (HTPE) bearing various functional side groups (e.g. carboxyl, ester and butane groups) were synthesized by the combination of ring-opening metathesis polymerization (ROMP) and visible light photocatalytic thiol-ene reaction. The products are named as α,ω-dihydroxyl-poly[(propionyloxythio)methinetrimethylene] (HTPE_carboxyl), α,ω-dihydroxyl-poly[(methylpropionatethio)methinetrimethylene] (HTPE_ester) and α,ω-dihydroxyl-poly[(butylthio) methinetrimethylene] (HTPE_butane), respectively. The investigation of ROMP indicated that the molecular weight of resultant hydroxyl-terminated polybutadiene (HTPB) can be tailored by varying the feed ratios of monomer to chain transfer agent (CTA). The exploration of the photocatalytic thiol-ene reaction between HTPB precursor and methyl 3-mercaptopropionate revealed that blue light as well as oxygen accelerated the reaction. ¹H-NMR and ¹³C-NMR results verified all the double bonds in HTPB can be modified, and the main chain of resultant polymer can be considered as polyethylene. Subsequently, relationship between the structure of side groups and the thermal properties of functional PEs was studied. And the results suggested that the T_g was in the order of HTPE_butane<HTPE_ester<HTPE_carboxyl. Greater interaction between side groups resulted in higher T_g. Moreover, all the functional PE samples exhibited poor thermostability as compared to HTPB. Finally, the promising applications for functional PEs were explored. HTPE_carboxyl can be utilized as a smart material with pH-responsive properties due to its pH-dependent ionization of carboxyl side groups. HTPE_butane can be employed as a macro-initiator for building the triblock copolymer due to the presence of active hydroxyl end groups. HTPE_ester can serve as a plasticizer for PVC which can enhance the ductility of PVC without obviously sacrificing strength.

Developing efficient, stable and sustainable photocatalysts for water splitting is one of the most significant methods for generating hydrogen. Conjugated microporous polymers, as a new type of organic semiconductor photocatalyst, have adjustable bandgaps and high specific surface areas, and can be synthesized using diverse methods. In this work, we report the design and synthesis of a series of pyridyl conjugated microporous polymers (PCMPs) utilizing polycondensation of aromatic aldehydes and aromatic ketones in the presence of ammonium acetate. PCMPs with different chemical structures were synthesized via adjusting monomers with different geometries and contents of nitrogen element, which could adjust the bandgap and photocatalytic performance. Photocatalytic hydrogen evolution rate (HER) up to 1198.9 μmol·h⁻¹·g⁻¹ was achieved on the optimized polymer with a specific surface area of 312 m²·g⁻¹ under UV-Vis light irradiation (λ>320 nm). This metal-free synthetic method provides a new avenue to preparing an efficient photocatalyst for hydrogen evolution.

Copolymerization is a commonly employed method for optimizing the properties of polymer materials. Incorporating ether segments into polyesters main chain to obtain polyether-polyester copolymers is an effective strategy to realize the integration of multiple properties of polyester and polyether, and to develop more high-performance, multi-purpose polymer materials. Herein, the synthesis of poly(ether-ester)s is accessible by employing the biphenyl-linked heterodinuclear salen Cr-Al complex in the presence of PPNCl for the copolymerization of epoxides and ε-caprolactone (CL). Monitoring the copolymerization process reveals that catalyst 1 exhibited good performance for the copolymerization of epoxides and CL, affording copolymers with a gradient sequence structure. The dynamic thermomechanical analysis (DMA) study indicates the obtained poly(ether-ester)s possess enhanced flexibility compared with the block copolymers or blend of PPO and PCL homopolymers with the same ratio. This study provides a theoretical basis for the preparation of high-performance polymer materials.

Medical devices-related infections pose a great threat to patients and cause an increased morbidity and mortality. Herein, we prepare an antibacterial composite (TPU-x) through blending medical grade thermoplastic polyurethane (TPU) and the complex (PL-DOSS) of ε-polylysine (ε-PL) and docusate sodium (DOSS). >99% reduction of colony forming unit (CFU) can be obtained in TPU-x composite films even at relatively low content of PL-DOSS, e.g. 0.13% for Methicillin resistant S. aureus (MRSA) and 0.5% for E. coli. The excellent antibacterial activity is mainly attributed to the formation of PL-DOSS nanoparticles that are uniformly dispersed in the TPU matrix with a size of ~100 nm. TPU-x composite films exhibit long-term stability in saline and good biocompatibility, and retain mechanical properties of TPU.

The novel amphiphilic graft copolymers with hydrophilic hard polar hydroxypropyl cellulose (HPC) backbone and hydrophobic soft nonpolar polyisobutylene (PIB) branches have been successfully synthesized through nucleophilic substitution reaction of living PIB chains carrying oxonium ions with the −OH groups along HPC backbone. The PIB branch length in the graft copolymers could be designed by living cationic polymerization and the grafting density could be adjusted by PIB⁺/−OH molar ratio. The living PIB chains carrying oxonium ion were prepared by transformation of allyl bromide end groups in the presence of AgClO₄ and silver nanoparticles (3.2±0.3 nm, 0.7 wt%−1.8 wt%) generated in situ from AgBr. The phase-separation morphology was formed in the graft copolymers due to their incompatibility between backbone and branches. The hydrophilicity on the surface of graft copolymer films could be turned to hydrophobicity by increasing grafting density or/and length of PIB branches. The soft PIB segments in graft copolymers provided an unique surface via self-assembly for anti-protein adsorption against bovine serum albumin. A small amount of Ag nanoparticles in the copolymers contributed to good antibacterial activities against Staphylococcus aureus or Escherichia coli.

Adding fumed silica (SiO₂) has been considered as an effective method for tailoring the phase morphology and performance of elastomer-toughened plastic binary blends. It has been demonstrated that the selective distribution of SiO₂ plays a decisive role in the mechanical properties of plastic/elastomer/SiO₂ nanocomposites, especially for the impact toughness. In this work, we aim to illuminate the role of specific surface area in controlling their selective distribution of fumed SiO₂ and consequent mechanical properties of plastic/elastomer binary blends. Three types of SiO₂ with different specific surface areas were incorporated into polylactide/ethylene-co-vinyl-acetate (PLA/EVA) model blends by melt blending directly. It was found that the selective distribution of SiO₂ is largely determined by their specific surface areas, i.e. SiO₂ nanoparticles with low specific surface area has a stronger tendency to be located at the interface between PLA matrix and EVA dispersed phase as compared to those with high specific surface area. The specific surface area-dependent interfacial selective distribution of SiO₂ is mainly attributed to the extent of increased viscosity of EVA dispersed phase in which SiO₂ nanoparticles are initially dispersed and resultant migration rate of SiO₂ nanoparticles. The interfacial localized SiO₂ nanoparticles induce an obvious enhancement in the impact toughness with strength and modulus well maintained. More importantly, in the case of the same interfacial distribution, toughening efficiency is increased with the specific surface area of SiO₂. Therefore, this is an optimum specific surface area of SiO₂ for the toughening. This work not only provides a novel way to manipulate the selective distribution of SiO₂ in elastomer-toughened plastic blends toward high-performance, but also gives a deep insight into the role of interfacial localized nanoparticles in the toughening mechanism.

Formation of shish-kebab crystals using a bimodal polyethylene system containing high molecular weight (HMW) component with different ethyl branch contents was investigated. In situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques were used to monitor the formation and evolution of shish-kebab structure sheared at low temperature in simple shear mode and low rate. Only the bimodal PE with no branch formed shish-kebab crystals at the shear temperature of 129 °C, and the shish length increased with the crystallization time, while bimodal PE with branch has no observable shish under the same conditions. The degree of crystallization for bimodal PE with no branch increased with time up to above 7%, while those with ethyl branch increased continually up to above 23%. Furthermore, bimodal PE's Hermans orientation factor with no branch increased to 0.60, while those with ethyl branch only increased to a value below 0.15. This study indicated that the shish-kebab crystal formed at the low temperature of 129 °C is due to the stretch of entangled chains under shear for the bimodal PE with no branch. Only partly oriented lamellar crystals were formed for the bimodal PE with ethyl branch. All the results at the shear temperatures higher, closed to, and lower than the melting point, the modulation of shish crystals formation owing to different mechanisms of the coil-stretch transition and the stretched network by changing shear temperature was achieved in the bimodal PE samples.

The influence of polystyrene particles with different nanoscale roughnesses on the morphology of polyisobutylene/polydimethylsiloxane blends was studied under shear flow by using confocal laser scanning microscopy. It was found that the surface roughness of particles strongly affected their diffusion and distribution behaviors, thereby determining the size and spatial arrangement of droplets in the blends. The roughness effect of particles was found to possess a strong dependence on both the blend ratio and the shear rate. The result suggested that the particle roughness can serve as a new parameter to control the structure-property correlation in particle-filled polymer blends, especially under slow flow.