Synthetic polypeptides, also known as poly(α-amino acid)s (PαAAs), are biomimetic and biodegradable polymers holding great potential for a variety of biomedical applications. Possessing the same peptide bonds as natural proteins, polypeptides can also adopt typical well-defined secondary structures including α-helix, which have been shown to significantly impact the physicochemical properties and biological outcomes of materials. In this feature article, we review the state-of-the-art progresses of α-helical polypeptides for biomedical applications, with a special emphasis on the manipulation of helix-to-coil dynamic transition, conformation-associated anti-biofouling coatings, cellular uptake regulation, and reducing immunogenicity of polypeptide-protein conjugates. Finally, perspectives on outstanding challenges remained in this field and some important future directions are discussed.

Sequenced-defined oligomer has been emerged as one of the hot topics in polymer chemistry due to its capability of precisely controlling both chain length and monomer sequence. Recent efforts have focused on development of synthetic methodologies using state-of-the-art chemistry tools. However, investigating the impact of minor changes in monomer sequence on physical properties of these materials is still underdeveloped. Herein, four sequenced pentamers are synthesized by a reversible addition-fragmentation chain transfer (RAFT) single unit monomer insertion technique, in which a base pentamer possesses a relatively rigid backbone comprising of five cyclic monomer units. One of the cyclic units in this base pentamer is replaced by an acyclic monomer at different locations (the 1^st, 3^rd and 5^th unit) to produce three modified pentamers, which leads to a significant decrease of glass transition temperature (T_g) compared to the base pentamer. Meanwhile, the modified pentamers with identical primary structures but distinct monomer sequences also present different T_g values depending on the position of the acyclic monomer unit. The middle (3^rd) position of the acyclic unit causes profound decrease of T_g due to its increased molecular flexibility. These synthetic pentamers have been demonstrated to be excellent oligomeric plasticizers to modulate thermal transitions of bulk polymer materials.

The emerging chemical recyclable polymers, such as poly(γ-butyrolactone) (PGBL) and poly((R)-3,4-trans six-membered ring-fused GBL) (P((R)-M)), provide a good solution to the plastic pollution. However, these homopolymers suffer from limited structures and properties. Herein, we reported a fully chemical recyclable copolymer P(GBL-co-((R)-M)) through ring-opening copolymerization (ROCOP) of GBL and (R)-M. By employing organomagnesium as the catalyst and regulating the reaction conditions, the chemical structures of copolymers were well-controlled (GBL content=13%−78%, M_n=6560−15600 g/mol, Ð_M=1.08−1.59). The resultant P(GBL-co-((R)-M)) exhibited fully chemical recyclability, which rapidly and quantitatively depolymerized into initial GBL and (R)-M monomer through chemolysis. By varying GBL content, tunable thermal properties were achieved for P(GBL-co-((R)-M)). The onset decomposition temperatures of copolymers varied from 193 °C to 234 °C. A linear evolution of glass transition temperature (T_g) of P(GBL-co-((R)-M)) versus GBL content was obtained as following equation of T_g = −1.06 × GBL mol% × 100 + 39.6. We hope that the reported fully chemical recyclable copolymers with tunable structures and properties would serve as the candidate material for sustainable applications.

Poly(propylene carbonate phthalate) (PPC-P) is a chemically modified poly(propylene carbonate) (PPC) biodegradable thermoplastic by introducing phthalic anhydride (PA) as the third monomer into the copolymerization of propylene oxide (PO) and CO₂. To enhance the thermal and mechanical properties of PPC-P, a branching agent pyromellitic anhydride (PMDA) was introduced into the terpolymerization of PO, PA and CO₂. The resulting copolymers with branched structure, named branched PPC-P, can be obtained using metal-free Lewis pair consisting of triethyl borane (TEB) and bis(triphenylphosphine)iminium chloride (PPNCl) as catalyst. The products obtained were analyzed by NMR spectro- scopy and their thermal, mechanical properties and melt processability were evaluated by DSC, TGA, tensile test and melt flow index (MFI) measurement. The obtained branched PPC-P has a high molecular weight up to 156.0 kg·mol⁻¹. It shows an increased glass transition tempera- ture (T_g) higher than 50 °C and an enhanced tensile strength as high as 38.9 MPa. Noteworthily, the MFI value decreases obviously, indicative of an improved melt strength arising from the branched structure and high molecular weight. What is more, the branched PPC-P exhibits reasonable biodegradability, which demonstrates the great potential as a new green thermoplastic for the family of biodegradable plastics.

The α-imino-ketone nickel catalyst is an emerging versatile platform that is easy to prepare and allows for the production of branched high molecular weight functionalized polyethylenes. However, study on this catalyst system is rare thus far. In this contribution, by introducing different backbones, flexible and rigid axial substituents into the α-imino-ketone framework, a family of cationic nickel catalysts were synthesized and fully characterized. Without the addition of any activator, systematic studies on ethylene polymerization and copolymerization with polar monomers were performed to explore the influence of both backbone and axial substituent on catalytic activity, polymer molecular weight, branching density and incorporation. In particular, owing to the unique semi-opening feature of the α-imino-ketone framework, the preferred nickel catalyst exhibited high activity of 175 kg·mol⁻¹·h⁻¹ to produce functionalized polyethylene with molecular weight of 13.4 kg·mol⁻¹ and co-monomer incorporation of 2.9 mol%.

The solventnatures are crucial to deeply reveal solution behavior of macromolecular chains, physical essence of condensed state structures formation of the film as well as the photoelectronic devices performance. Based on the second virial coefficient (A₂), effect of the synergistic action of solvents and external electric field on both solution behavior and the film’s condensed state structure for the semi-rigid conjugated polymer, poly[2-methoxy-5-(2'-ethylhexoxy)-1,4-phenylvinylene] (MEH-PPV) was investigated by dynamic/static light scattering, photoluminescence spectroscopy and transmission electron microscopy, etc. It was found that although the MEH-PPV solutions with different solvents (toluene, chlorobenzene, chloroform and tetrahydrofuran) all could generate a response to the external electric field, the degree of response varied significantly with the change of solvent nature. Furthermore, ordered degree of the film from the solutions was also obviously different. The essential reason for this responsive difference was firstly revealed in the research, which actually depended on the degree of interaction between the solute and solvent, and this degree of interaction could be quantitatively described by the second virial coefficient (A₂). The bigger the A₂, the stronger the interaction between solvent and solute in the solution, and the stronger the response to the external electric field. Further, under the induction of external electric field, chains aggregations with different sizes were formed accompanied by large-scale chains ordered structure in the solution. This ordered structure not only can effectively transfer to film prepared by the precursor solution but also is beneficial to enhance the carrier mobility and device efficiency of the photoelectronic film.

Improvement of the treatment for Glioblastoma multiforme (GBM) especially the development of in situ controllable drug release is still a major concern. In this study, we developed waterborne biodegradable polyurethane (WBPU) scaffolds incorporated with redox-sensitive and RGD-decorated paclitaxel (PTX) polymer-drug conjugates (PDCs) for targeted GBM therapy in situ. The drug scaffolds could be implanted at residual GBM site post-operation. Dual-targeting PTX-PDCs were obtained through step-by-step conjugation of disulfide linked PTX, poly(ethylene glycol) (PEG), and arginine-glycine-aspartic acid (RGD). The RGD-modified PTX-PDCs were spherical nanoparticles (NPs) that would be released from scaffolds and identified GBM cells actively. Internalized redox-sensitive PTX-PDCs would be decomposed and release PTX inside GBM cells under the circumstances of glutathione (GSH). The release profiles of PTX from the scaffolds with/without GSH were investigated. In vitro cytotoxicity assay revealed that the dual-targeting PTX-PDCs from scaffolds could specifically kill GBM cells and protect normal cells, suggesting that dual-targeting PTX-PDC-loaded scaffolds may have the potential to repair tumor-induced brain injury. In vivo anti-recurrence assay indicated that the PTX-PDC-scaffolds could deliver PTX-PDCs to the GBM cells followed by inhibiting tumor growth and inducing apoptosis. In general, the PTX prodrug-loaded devices exhibited significant anti-GBM effects and normal tissue protection simultaneously, indicating that the WBPU scaffolds incorporated with dual-targeting PTX-PDCs may be a promising strategy for local therapy of GBM.

The changes of crosslinking network of perfluorinated elastomer (FFKM) cured by TAIC and DBPH under thermo-oxidative aging conditions were investigated. Two competitive processes including post-curing and network destruction occur simultaneously, which directly affect the storage modulus and crosslinking density. With the increase of aging temperature, the network destruction becomes dominant. FTIR and XPS characterizations further reveal that the network destruction happens preferentially on the crosslink points of TAIC structure, and the post-curing is mainly caused by the decomposition of residual curing agent DBPH. Unlike the easier breaking of TAIC structure in the crosslinking network, both the backbone and the pendent groups of FFKM itself are much more stable. To further figure out the destruction mechanism, TGA-FTIR-GC-MS test was also conducted and a schematic degradation process of TAIC structure was proposed. It is found that the destruction of TAIC crosslinking points happens first on the unstable exocyclic C―N bonds and the intermediate ring radicals could eventually decompose into volatile hydrogen isocyanate (HCNO) under extreme condition.

High-performance dielectric polymer composites have received increasing attention due to their important applications in the field of energy storage. The rational structural design of hybrid fillers can lead to a balance between high dielectric constant and insulation in composites. In this work, novel hybrid fillers were fabricated byin situ synthesizing one-dimensional polypyrrole nanowires (PPynws) on the two-dimensional molybdenum disulfide (MoS₂), which integrated the good ion polarization ability of PPynws and the high insulation and adjustable band gap of MoS₂. Compared with the binary poly(vinylidene fluoride) (PVDF)/MoS₂ composites, the PVDF/MoS₂-PPynws composites exhibited remarkably improved dielectric constant and breakdown strength, while the dielectric loss was still maintained at a low level. An optimal ternary composite with 1 wt% MoS₂-PPynws showed a high dielectric constant (15@1kHz), suppressed dielectric loss (0.027@1kHz), and high breakdown strength (422.1 MV/m). PPynws inducing strong interfacial polarization and the highly insulated MoS₂ nanosheets extending the breakdown path mainly contributed to the synchronously enhanced dielectric constant and breakdown strength. This intriguing synthesis method of PVDF/MoS₂-PPynws nanocomposite will open up new opportunities for fabricating nanostructured polymer composites to produce high dielectric materials.

A new method for characterizing fiber bending flexibility was developed by worm-like chain model proposed by Kratky-Porod,^[1] which was first introduced to the pulp and paper field in this study. For the three types of pulps, the experimental results were compared with the KP chain model, and the resulting determination coefficients were all above 0.95, which proved that the model was feasible to be applied to these three fibers. The relation between fiber bending rigidity and that of cellulosic chains inside was discussed to deduce the fiber bending flexibility. The flexibility of an individual fiber can be approximated as the contribution of that of all the cellulose chains inside. By this method, the fiber flexibility values were determined to be in the range of 0.6×10¹¹−3.5×10¹¹ N⁻¹·m⁻², which was comparable to that of the conventional methods recorded in the literature.

The effect of viscosity of non-translocated (cis) side, η_cis, on the driven translocation of charged polymers through nanopores is investigated using Langevin dynamics simulation. Results show that the translocation of polymer chains can be regulated by changing η_cis. As η_cis decreases, the translocation time τ decreases, and the exponent δ in the scaling relation with driving force f, τ~f^−δ, increases whereas α in the scaling relation with chain length N, τ~N^α, decreases. Simultaneously, the conformation of the polymer chain at the cis side gravitates towards an equilibrium state. The results imply a relationship between the translocation and the conformation of polymer chains. To verify this hypothesis, we change the conformation of polymer by artificially relaxing the translocating polymer via adding an additional relaxation time in the simulation. A sufficient large additional relaxation time for the translocating polymer chain at the cis side only or at both cis and trans sides results in exponents α and δ both close to 1, in contrast to α=1.36 and δ=0.8 for the translocation without the additional relaxation. The additional relaxation for the polymer chain at the cis side accelerates the translocation and plays a more important role than that for polymer chain at the trans side.