A photo-controlled approach is developed to regulate the interpenetrating polymer network (IPN) topology by varying the connecting structure between the first and second networks. The approach is based on multifunctional inimer (Vinyl-oNB-Br) possessing three moieties, i.e., an acrylate-based double bond for incorporation within a polymer network, a Br group for grafting polymerization to get connect-IPN (c-IPN), and an o-nitrobenzyl spacer for photocleaving to convert the c-IPN to disconnected-IPN (d-IPN) with UV light irradiation. Such design allows for finely controlling the connection degree between two networks. A systematic study on the mechanical property of a series of samples with different connection degrees thus can be conducted. The results reveal that decreasing the connecting degree between two networks of IPN made a negligible contribution to materials’ mechanical properties.

Flexible, breathable and lightweight electronic textiles hold great promise to change the ways we intact with electronics. Electrical connections among functional components are indispensable for system integrations of electronic textiles. However, it remains challenging to achieve mechanically and electrically robust connections to fully integrate with interwoven architecture and weaving process of textiles. Here, we reported a seamlessly-integrated textile electric circuit by weaving conductive fibers with self-connecting capacity at the interwoven points. Self-connecting conductive fibers (SCFs) were prepared by coating modified polyurethane conductive composites onto nylon fibers. Electrical connections were achieved at interwoven points in less than 5 s once the weft and warp SCFs were woven together, due to the designed dynamic bonds of aromatic disulfide metathesis and hydrogen bonds in the modified polyurethane (MPU). The self-connecting point was electrically stable (varied by less than 6.7% in electrical resistance) to withstand repeated deformations of bending, pressing and even folding. Such a self-connecting strategy could be generalized to weave full-textile electronics capable of receiving signals and displaying with enhanced interfacial stability, offering a new way to unify fabrication of electronics and weaving of textiles.

The ring-opening alternating copolymerization processes of epoxides with small-molecule monomers, such as carbon dioxide (CO₂), carbonyl sulfide (COS) and cyclic anhydrides, are powerful strategies for preparing polymeric materials with degradable carbonate/ester/thiocarbonate main-chain backbone units. The catalysts selected for copolymerization processes play crucial roles in determining their reaction rates and productivities, as well as the selectivity, regio- and stereochemistry, compositions, and the molecular weights of their resultant copolymers. These processes often generate undesirable byproducts such as polyether or ether linkages dispersed randomly within the copolymer’s chain, and/or more thermodynamically stable cyclic products. In this account, we outline our efforts of over a dozen years on developing highly active well-defined metal catalysts based on inter- and intra-molecular synergistic strategies to selectively produce completely alternating copolymers from epoxides and various small-molecule monomers. Much attention was paid to the enantioselective resolution copolymerization processes of racemic epoxides via regioselective ring-openings, and the asymmetric copolymerization processes of meso-epoxides with CO₂, COS, or cyclic anhydrides via dissymmetrical ring-openings using multichiral catalytic systems, and affording isotactic copolymers with main-chain chirality. In addition, this account provides a thorough mechanistic understanding of the high reactivities, excellent selectivity, and unprecedented stereochemical controls of these copolymerization systems, mediated by inter- and intramolecular synergistic catalysis.

A novel boron-containing monomer, (4-(3,4-dicyanophenoxy)phenyl)boronic acid (BPhPN) was synthesized and used to promote the curing process of phthalonitrile monomer 1,3-bis(3,4-dicyanophenoxy)benzene (MPN). Differential scanning calorimetry and rheological analysis were used to study the curing behaviors of BPhPN/MPN (namely B-MPN), and results suggested that B-MPN systems have better processibility. FTIR spectra and solid-state ¹³C-NMR exhibited triazine and isoindoline have been formed in the curing process. Boron-containing Lewis acid curing mechanism was preliminarily speculated and verified by two model compounds with different boron chemical environments. The thermogravimetric analysis and dynamic mechanical analysis demonstrated that the cured B-MPN polymers showed excellent thermal stability and heat resistance, which were comparable with conventional catalytic systems for phthalonitrile resins. This study not only presented a novel curing system for phthalonitrile resins, but also shed light on future design of high temperature thermosets.

Modifications at polypeptide side chains have been found to affect conformational and properties, which is a vital strategy to prepare functional polypeptides. This contribution describes the synthesis of homo and co-polypeptides containing unsaturated bonds and thioether moieties, poly(S-allylcysteine) (PAC). The pendant vinyl groups provide an active binding site which are able to be further modified with cysteine by thiol-ene click reaction. The sulfoxide from thioether oxidation bestows the polypeptide water solubility and enzymatic catalytic sites. The self-assembly micelles of PEG-b-PAC are ruptured along with oxidation to release the Nile red payloads. Moreover, poly(S-allyl-cysteine sulfoxide), aka. polyalliin, is the oxidation product of PAC which undergoes side chain cleavage catalyzed by alliinase enzyme. The polypeptides are biocompatible as confirmed by cell viability assays and may find applications in drug delivery, biosensing and nanoreactor.

A family of highly bulky bis(salicylaldiminate) Co(II) complexes bearing cavity-like conformations are disclosed herein. Due to their unique bulky nature around the cobalt atoms that are reflected from space-filling models and the buried volume percentages, obviously longer bond distances of Co―N and Co―O are revealed from those complexes. Moreover, because of these well-protected active species, the cobalt complexes are able to catalyze 1,3-butadiene polymerization in high yields at extreme low catalyst concentrations, revealing a ultra high catalytic efficiency. At a ratio of 50000, all the complexes can afford polybutadiene with yields higher than 90%. Furthermore, the highly steric bulkiness of the ligand can also significantly enhance the thermostability of the active species. At temperature of 80−120 °C, the complexes are able to successfully maintain high activities, giving polymer yields up to 90%.

Developing thermal management fabrics with good energy storage and multistimuli responsive properties is important for regulating the body temperature in complex environment. Herein, the intelligent nonwoven membranes were fabricated via a coaxial electrospinning method, resulting in a core-sheath structure with poly(ethylene glycol) (PEG) as core and polyurethane (PU) as sheath. Additionally, polypyrrole (PPy) with good light absorption ability and electrical conductivity was deposited onto the surface of the PU@PEG electrospun fibers via electrochemical polymerization. The PPy layer enabled the membranes to respond quickly to sunlight and electrical stimuli. The membranes could heat up to 86 °C under simulated sunlight within 200 s or produce remarkable electrothermal effect under a low voltage input of only 1 V, exhibiting efficient energy conversion and storage performances. The photothermal and electrothermal conversion effect could be easily adjusted by controlling the polymerization time of PPy. Therefore, the multifunctional membranes with high latent heat, good mechanical properties as well as excellent photothermal/electrothermal conversion ability are promising in personal thermal management applications.

The dissatisfactory mechanical compliance between stiff polypropylene (PP) and soft human tissue is one of the main factors causing the implanted complication of PP mesh devices such as chronic abdominopelvic pain and mesh exposure. This work aims to improve the mechanical compliance of PP monofilament to human tissue without compromising the mechanical properties by elaborating polyurethane pillowy soft mat on the PP monofilament surface. Combining polarity pretreatment with dopamine-sedimentation, stiff PP monofilament can be wrapped up facilely and tightly in soft polyurethane to obtain PU/PP complex fiber with a core-shell structure. Notably, the interfacial shear strengths (IFSS) between stepwise treated PP monofilament and PU mat can effectively increase 586% compared to raw PP. This work provides a promising surface modification strategy to improve the interfacial adhesion between PP monofilament and PU mat. The obtained novel PU/PP complex fiber with pillowy soft mat would be a potential application in abdominal wall defects, hernia repair and pelvic organ prolapsed surgery.

Poly(vinyl alcohol) (PVA) is usually processed and used in a form of aqueous dispersion. A large number of inter- and intramolecular hydrogen bonds make it very difficult to obtain suitable rheological behavior for processing. In this study, carbon particles with different topological shapes were added into PVA aqueous dispersion to tune the steady and dynamic rheological behavior. The results show that the zero-dimensional particles (carbon black, CB) increase monotonically the zero-shear viscosity of PVA dispersion, while the one-dimensional particles (carbon nanotubes, CNTs) make it first increase, and then decrease and rise again, like an N-shape, and the two-dimensional particles (graphene oxide, GO) can make it first decrease and then increase, exhibiting a U-shape. It is believed that the topological shape of the carbon particles brought about these discrepancies. The zero-dimensional particles mainly act as physical crosslinking points due to their small size. While at a certain content, both CNTs and GO can destroy the intermolecular hydrogen bonds between PVA chains because the PVA chains can twine around the slim CNTs and the large planar size of GO prevents the adsorbed PVA from forming hydrogen bond with other chains. The high hydroxyl value of carbon particle surface could strengthen this effect. It is expected that the viscosity of polymer dispersion can be regulated by particles with different topological shape and the surface characteristic, so as to widen the operable concentration range during preparing composite functional materials.

Well-defined polypropylene grafted silica nanoparticles (PP-g-SiO₂) were prepared through the reaction of maleic anhydride grafted polypropylene (PP-g-MAH) with amino-functionalized silica (SiO₂-NH₂) by the 'grafting-to' method. The grafting density of PP-g-SiO₂ is found to be controlled by the concentration of silane coupling agent 3-[2-(2-aminoethylamino) ethyl amino] propyl trimethoxy silane (TAMS). The maximum grafting density of grafted PP-g-MAH chains with molecular weight of 9100 g/mol could reach 0.34 chains/nm², when the critical concentration of TAMS was 0.0194 mol/L. The critical concentration of TAMS can be explained by the maximum amounts of primary amino groups, which can totally react with PP-g-MAH on the surface of SiO₂-NH₂, when the silane monolayer is formed. The synthesized PP-g-SiO₂ with different molecular weights was mixed with PP by solution mixing to form a series of nanocomposites. The crystallization temperature (T_c) of nanocomposites increased significantly with the particle loading. The PP-g-SiO₂ with high molecular weight of grafted chains exhibits a high nucleation ability at 1 wt% nanoparticle loading in PP/PP-g-SiO₂ nanocomposites. In summary, we provide an effective method to synthesize the well-defined PP-g-SiO₂ with controlled grafting density, which shows excellent nucleation ability.

Polymer fiber with an ultrahigh thermal stability, superior flame retardancy and low smoke release during combustion is urgently needed and a crucial challenge for developing advanced fireproof textiles. In this study, a series of high-performance polyimide fibers are synthesized by copolymerizing 4,4'-diaminodiphenylmethane (MDA) into the pyromellitic dianhydride-p-phenylenediamine (PMDA-PDA) backbone for synergistically solving the technical challenge of poor fiber processing ability of these polyimides with a high inherent molecular rigidity. The glass transition temperature (T_g) of resultant fibers with the PDA molar ratio over 50 mol% reaches above 420 °C and their 10 wt% weight loss temperature (T_10%) is within 543−633 °C. For the typical fiber containing 80 mol% of PDA, the limiting oxygen index (LOI) reaches 39% and exhibits a rapid self-extinguishing performance after deviating from the flame. Meanwhile, this fiber exhibits the minimum heat release rate of 14.1 kW/m² in a long ignition time of 813 s during combustion, revealing its better flame retardancy than the well-known Nomex fiber with a heat release rate of 140.6 kW/m² during the 120 s ignition. Meanwhile, the total smoke production of this polyimide fiber is only 1/9 of the Nomex fiber. Accordingly, the excellent flame retardancy of polyimide fibers indicating them more attractive as the fireproof materials in the field of emergency protection.

A great progress has been made over the last decades in studying concentration scaling on rheometric properties of monodisperse polymer solutions. However, the effects of polydisperse polymer solutions on such a concentration scaling remain elusive. In this work, rheometric properties of industrially relevant polydisperse and high molecular weight polyacrylamide (PAAm) aqueous solution have been studied. The results show a concentration scaling of the characteristic relaxation time, the plateau modulus and the zero-shear viscosity across a concentration range from 10c* to 250c*. The time-concentration superposition principle is validated and extended in the data analysis of the terminal dynamic regime. The concentration scaling exponent of their shifting factors is significantly smaller than the results of monodisperse polymer solutions in good and θ solvents reported in the literature. The steady shear viscosity and shear stress of 18M PAAm aqueous solutions with relatively lower concentration (≤35c*) could also be superimposed into a master curve with the shear-thinning exponent of 0.73±0.03 and 0.27±0.03, respectively, over a wide range of shear rates in about six orders of magnitudes. However, for 18M PAAm aqueous solutions with higher concentration (≥48c*) in an intermediate shear thinning regime, the scaling exponent shows a pronounced concentration dependence. The shear thinning exponent of steady shear viscosity varies from 0.73 to 0.57 as concentration is increased, and then increases from 0.57 to 0.90 from sufficiently high shear rate. Further increasing shear rate, the shear-thinning exponent of 18M PAAm aqueous solutions at all concentrations converges to the lower bounded value observed in the relatively less concentrated (≤35c*) 18M PAAm aqueous solutions, i.e., 0.73±0.02 for shear viscosity and 0.27±0.02 for steady shear stress, respectively. It reveals that the concentration effects of polydisperse polymer solutions could be greatly reduced by the dynamic "molecular individualism” in strong shear flow.

High-quality film capacitors are widely used in many fields such as new energy vehicles, electronic communications, etc., due to their advantages in wide frequency response and low dielectric loss. The dielectric film is a crucial part of the film capacitor, and its properties have an important impact on the performance and use conditions of the film capacitor. In this work, a novel high-temperature-resistant dielectric film was prepared. Firstly, the Bi₂S₃/rGO-CN fillers were prepared by hydrothermal method combined with cyanation treatment, and then added to the poly(arylene ether nitrile) (PEN) matrix to prepare the dielectric film materials (PEN/Bi₂S₃/rGO-CN). After high temperature treatment, the fillers Bi₂S₃/rGO-CN reacted with the PEN matrix, and the composites materials transformed into a thermosetting hybrid film (PEN-Bi₂S₃/rGO) with gel content of 97.88%. The prepared hybrid dielectric films did not decompose significantly before 400 °C, and showed a glass transition temperature (T_g) of up to 252.4 °C, which could increase the effective use temperature of the materials. Compared with the composite films without heat treatment, they exhibit better mechanical properties, with further improvement in tensile strength and elastic modulus, and a decrease in elongation at break. The dielectric constant of the hybrid films can be up to 6.8 while the dielectric loss is only about 0.02 at 1 kHz. Moreover, the hybrid films showed excellent dielectric stability during temperature changes, and remain relatively stable before 250 °C, which is suitable as a high-temperature-resistant high-dielectric material and is more advantageous for practical applications.

It is known that the enhanced melt memory effect is strongly correlated with the retarded chain dynamics. However, previous studies using differential scanning calorimetry (DSC) showed a weakened or even vanished melt memory in polymer nanocomposites, although adding nanoparticles in polymers often reduces chain mobility. In this work, we added two kinds of silica nanoparticles, O15 and W22 nanoparticles (with low and high surface silanol density, respectively), to poly(ε-caprolactone) (PCL), where the degree of chain entanglements near nanoparticles increases, and chain dynamics is gradually retarded with increasing silica content. The strongly aggregated W22 nanoparticles show significant heterogeneous nucleation, while well-dispersed O15 nanoparticles exhibit very weak heterogeneous nucleation. In contrast to the restrained self-nucleation effects during the rapid non-isothermal crystallization of two nanocomposites, we found evident melt memory effects during the slow isothermal crystallization in PCL/O15 nanocomposites as indicated by DSC and polarized light microscopy (PLM) measurements. The melt memory becomes stronger with more O15 nanoparticles, but depends non-monotonically on the loadings of W22 nanoparticles. The lifetime of the melt memory effects matches the chain re-entanglement time of the SN melts of nanocomposites, which is consistent with our previous work on PCL miscible blends. The complicated influence of silica on nucleation and crystal growth is induced by the spatial inhomogeneity of chain entanglements in the silica-filled PCL system. The decrease in the entanglement density of the interfacial chains in the SN melts of nanocomposites is conducive to nucleate under slow isothermal crystallization, but the chain mobility is still greatly restrained by the nanoparticles, causing the slow growth rate of spherulites and the difficulty to form nuclei under fast non-isothermal crystallization.

Due to their excellent dielectric properties and the rapid response to microwave irradiation, silicon carbide nanowhiskers (SiCNWs) were employed as microwave susceptor in this study to absorb microwave and locally melt the surrounding polypropylene (PP) substrates for the joining of PP substrates. Complete welded joint is formed after the melted PP was cooled and resolidified. Other than microwave susceptor, SiCNWs also acted as the nanofillers in strengthening the welded joint through the formation of SiCNWs reinforced PP nanocomposite at the interface of PP substrates. Besides, the effect of microwave power on the microwave welding of PP substrates using SiCNWs as susceptor was studied and reported. It was found that the tensile strength and modulus of elasticity of the welded joint improved as microwave power increased. However, it deteriorates the flexibility of the welded joint as high stiffness SiCNWs were incorporated deeper into the PP matrix which restricted the PP chain mobility. Aside from microwave power, clamping pressure is also critical in determining the mechanical properties of a welded joint. When compared to unclamped welded joint, the tensile strength, modulus of elasticity and flexibility of welded joint subjected to clamping pressure improved drastically. Moreover, the tensile strength of welded joint increased when the clamping pressure was increased from P1 to P3, but decreased when the clamping pressure was further increased to P4 due to the occurrence of flashing at welded joint. The formation mechanism of SiCNWs reinforced PP welded joint was also proposed in this study. Compared to conventional welding, this welding process is easy, straightforward and is able to produce welded joint with outstanding mechanical properties via precise controlling of the processing parameters. Thus, microwave welding is thought to offer an option for the joining of thermoplastics and other applications.

Nanocomposites of blends of biodegradable poly(butylene adipate-co-terephthalate) (PBAT) and sustainable poly(propylene carbonate) (PPC) with nanosilica were prepared by melt compounding method. PBAT/PPC blend was partially miscible system with sea-island structure, and nanosilica particles were selectively dispersed in the continuous phase PBAT matrix to form the double percolation network. The introduction of nanosilica into PBAT/PPC blend reduced the size of dispersed PPC phase, promoted the crystallization of PBAT in the nanocomposites, and increased the storage modulus of the nanocomposites. The study of rheological behaviors indicated that the double percolation network was formed at the nanosilica loading of 5 wt%, as a result, the nanocomposites exhibited the solid-like viscoelastic behavior and their relaxation time was extended. With the increase of the nanosilica content, the PBAT/PPC/silica nanocomposites displayed increased Young’s modulus and yield strength.

Despite growing interest in nano-sized fillers, micro-sized fillers with desired compatibility are still used for reinforcing rubbers, owing to their lower production cost and easier processing relative to nano-sized fillers. Especially, the abundant and eco-friendly clay minerals are recognized as the materials of the twenty-first century. Herein, illite, a naturally occurring clay having dimension in micrometric scale, has been selected as filler to reinforce the SBR. To improve the compatibility of illite with SBR, the illite was modified by either bis[3-(triethoxysilyl)propyl] tetrasulfide (Si69-illite) or 3-mercaptopropyltriethoxysilane (KH580-illite). The interfacial interactions of SBR composites filled with pristine illite (illite/SBR) and Si69-illite (Si69-illite/SBR), or KH580-illite (KH580-illite/SBR) were characterized by bound rubber content and Payne effect measurements, while dynamic hysteresis losses of these uncured and cured composites were also analyzed under various strain amplitudes. It was found that the filler-rubber interactions were greatly improved for Si69-illite/SBR and KH580-illite/SBR systems compared to the illite/SBR composite. This leads to an increment of modulus at 300% strain of the composites from 3.46 MPa for illite/SBR to 7.70 MPa for Si69-illite/SBR and 12.96 MPa for KH580-illite/SBR. Moreover, lower rolling resistance and better wear resistance without compromising wet traction of Si69-illite/SBR and KH580-illite/SBR have been achieved. This demonstrates the high possibility of Si69 and KH580 modified illites as promising alternative fillers for reinforcing rubbers.

High-performance compression sensors have been playing an increasingly important role in human motion detection, health monitoring and human-machine interfaces over recent years. However, it remains a great challenge to develop theoretical models providing practical guidance to the sensor design. Herein, carbon black (CB), carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) were respectively incorporated into porous melamine sponges by a facile approach of dip-coating to fabricate compression sensors. Uniaxial compression-resistance tests show that the compressibility, stability and piezoresistive sensitivity of sensors could be tailored by the filler type and concentration. A model considering the number of conductive pathways (NCP) is given to describe the relationship between the resistance change and applied compression, showing extremely good agreement with the experimental data. Also, the correlation between the equivalent filler volume fraction and conductivity is described by the other two models proposed by McLachlan and Kirkpatrick, revealing the electrical percolation thresholds (Φ_c) for the conductive systems under compression. Among the three fillers, CB particles endowed the composite with the best piezoresistive sensitivity but the largest Φ_c due to its small size and aspect ratio. A combination of experimental study and theoretical model opens up a way of further understanding the piezoresistive sensing behavior as well as optimizing the electrical property and piezoresistivity of compressive conductive polymer composite.