Chinese Journal of Polymer Science最新文献

In this work, a morphology transition mode is revealed in ultra-high molecular weight polyethylene (UHMWPE) when stretching at 120 °C: moving from the slightly deformed region to the necked region, the morphology transfers from small spherulites to a mixture of transcrystalline and enlarged spherulites, and finally to pure transcrystalline; meanwhile, the lamellae making up the transcrystalline or spherulite were fragmented into smaller ones; spatial scan by wide-angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS) revealed that the crystallinity is increased from 25.3% to 30.1% and the crystal orientation was enhanced greatly, but the lamellae orientation was quite weak. The rise of enlarged spherulites or a mixture of transcrystalline and spherulites can also be found in UHMWPE stretched at 140 and 148 °C, whereas absent in UHMWPE stretched at 30 °C. In situ WAXS/SAXS measurements suggest that during stretching at 30 °C, the crystallinity is reduced drastically, and a few voids are formed as the size increases from 50 nm to 210 nm; during stretching at 120 °C, the crystallinity is reduced only slightly, and the kinking of lamellae occurs at large Hencky strain; during stretching at 140 and 148 °C, an increase in crystallinity with stretching strain can be found, and the lamellae are also kinked. Taking the microstructure and morphology transition into consideration, a mesoscale morphology transition mode is proposed, in the stretching-induced crystallization the fragmented lamellae can be rearranged into new supra-structures such as spherulite or transcrystalline during hot stretching.

Some novel manganese and nickel complexes were synthesized by reacting manganese(II) dichloride and nickel(II) dichloride with pyridyl-imine ligands differing in the nature of the substituents at the imino nitrogen atom. All the complexes were characterized by analytical and infrared data: for some of them single crystals were obtained, and their molecular structure was determined by X-ray diffraction. The complexes were used in association with methylaluminoxane (MAO) for the polymerization of 1,3-butadiene obtaining active and selective catalysts giving predominantly 1,2 polybutadiene in case of manganese catalysts and exclusively cis-1,4 polybutadiene in case of nickel catalysts.

Long-chain polyamides (LCPAs) are a class of bio-based polymers that can bridge conventional polyolefins and polycondensates. In this work, taking the advantage of the amphiphilic nature of polyamide 1012 (PA1012), membranes were prepared by using a non-conventional phase separation approach, namely, mixed ‘non-solvents’ evaporation induced phase separation (MNEIPS). PA1012 can be dissolved in a mixture of polar and non-polar solvents, both of which are non-solvents of PA1012. During the sequential evaporation of the two solvents, the phase separation of PA1012 occurred, inducing the formation of porous structures. We investigated the process of membrane formation in detail, with a specific focus on the liquid-liquid and liquid-solid phase transitions involved. Moreover, we studied the influence of critical factors, such as polymer concentration and mixed-solvent ratio, on the morphologies and properties of PA1012 membranes. This study provides new insights into the development of porous materials based on long-chain polycondensates.

The construction of monodisperse microporous organic microspheres is deemed a challenging issue, primarily due to the difficulty in achieving both high microporosity and uniformity within the microspheres. In this study, a series of fluorinated monodisperse microporous microspheres are fabricated by solvothermal precipitation polymerization. The resulting fluorous methacrylate-based microspheres achieved higher than 400 m²/g surface area, along with a yield of over 90% for the microspheres. Through comprehensive characterization and simulation methods, we discovered that the introduction of fluorous methacrylate monomers at high loading levels is the key factor contributing to the formation of the microporosity within the microspheres. The controlled temperature profile was found to be advantageous for achieving a high yield of microspheres and increased uniformity. Two-dimensional assemblies of these fluorinated microsphere arrays exhibited superhydrophobicity, superolephilicity, and water sliding angles below 10°. Furthermore, a three-dimensional assembly of the fluorinated microporous microsphere in a chromatographic column demonstrated significant improvement in the separation of Engelhardt agent compared to commercial columns. Our work offers a novel approach to constructing fluorinated monodisperse microporous microspheres for advanced applications.

In this study, a novel cost-effective methodology was developed to enhance the gas barrier properties and permselectivity of unfilled natural rubber (NR)/polybutadiene rubber (BR) composites through the construction of a heterogeneous structure using pre-vulcanized powder rubber to replace traditional fillers. The matrix material is composed of a blend of NR and BR, which is widely used in tire manufacturing. By incorporating pre-vulcanized trans-1,4-poly(isoprene-co-butadiene) (TBIR) rubber powder (pVTPR) with different cross-linking densities and contents, significant improvements in the gas barrier properties and CO₂ permselectivity of the NR/BR/pVTPR composites were observed. The results indicated that compared to NR/BR/TBIR composites prepared through direct blending of NR, BR, and TBIR, the NR/BR/pVTPR composites exhibited markedly superior gas barrier properties. Increasing the cross-linking density of pVTPR resulted in progressive enhancement of the gas barrier properties of the NR/BR/pVTPR composite. For example, the addition of 20 phr pVTPR with a cross-linking density of 346 mol/m³ resulted in a 79% improvement in the oxygen barrier property of NR/BR/pVTPR compared to NR/BR, achieving a value of 5.47×10⁻¹⁴ cm³·cm·cm⁻²·s⁻¹·Pa⁻¹. Similarly, the nitrogen barrier property improved by 76% compared to NR/BR, reaching 2.4×10⁻¹⁴ cm³·cm·cm⁻²·s⁻¹·Pa⁻¹, which is 28 % higher than the conventional inner liner material brominated butyl rubber (BIIR, P_N2=3.32×10⁻¹⁴ cm³·cm·cm⁻²·s⁻¹·Pa⁻¹). Owing to its low cost, exceptional gas barrier properties, superior adhesion to various tire components, and co-vulcanization capabilities, the NR/BR/pVTPR composite has emerged as a promising alternative to butyl rubber in the inner liner of tires. Furthermore, by fine-tuning the cross-linking density of pVTPR, the high-gas-barrier NR/BR/pVTPR composites also demonstrated remarkable CO₂ permselectivity, with a CO₂/N₂ selectivity of 61.4 and a CO₂/O₂ selectivity of 26.12. This innovation provides a novel strategy for CO₂ capture and separation, with potential applications in future environmental and industrial processes. The multifunctional NR/BR/pVTPR composite, with its superior gas barrier properties and CO₂ permselectivity, is expected to contribute to the development of safer, greener, and more cost-effective transportation solutions.

Melt pre-shear induced crystallization of polymer blends holds great significance in industrial processing and product application. In this work, two typical PB/PP blends (50/50, 90/10), possessing commercial value and academic hotspot, were employed to investigate the effect of melt pre-shear on the crystallization of isotactic poly(1-butene) (PB) and polypropylene (PP) by applying shearing slightly above the melting temperature of PP with subsequent non-isothermal crystallization to simulate actual processing conditions. It was discovered that in PB/PP (90/10) blend, in situ melt pre-shear generated oriented PP precursors induced the formation of PP-FIC (Flow-induced crystallization) which acted as row crystal nucleus significantly promoting PB crystallization into spherulite with higher melting temperatures (T_m), crystallinity (X_c), and thicker lamellar thickness (d_c). While in PB/PP (50/50) blend, the melt pre-shear generated PP-shish precursors induced the formation of PP shish-kebab that exerted a confining effect on the crystal growth of PB, resulting in truncated spherulite formation with higher T_m and thicker d_c but lower X_c. This research provides insight into the mechanism underlying oriented crystal structure formation, crystal properties, and phase morphology of PB/PP blends under melt pre-shear fields, which have significant theoretical and practical implications for their industrial processing and preparation of high-performance products.

Machine learning-assisted prediction of polymer properties prior to synthesis has the potential to significantly accelerate the discovery and development of new polymer materials. To date, several approaches have been implemented to represent the chemical structure in machine learning models, among which Mol2Vec embeddings have attracted considerable attention in the cheminformatics community since their introduction in 2018. However, for small datasets, the use of chemical structure representations typically increases the dimensionality of the input dataset, resulting in a decrease in model performance. Furthermore, the limited diversity of polymer chemical structures hinders the training of reliable embeddings, necessitating complex task-specific architecture implementations. To address these challenges, we examined the efficacy of Mol2Vec pre-trained embeddings in deriving vectorized representations of polymers. This study assesses the impact of incorporating Mol2Vec compound vectors into the input features on the efficacy of a model reliant on the physical properties of 214 polymers. The results will hopefully highlight the potential for improving prediction accuracy in polymer studies by incorporating pre-trained embeddings or promote their utilization when dealing with modestly sized polymer databases.

A series of transparent crosslinked colorless polyimide (CPI) films are prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2,2′-bis(trifluoro-methyl)benzidine (TFMB), and 4,4′-oxydianiline (ODA) by thermal imidization, incorporating varying contents of 2,2′-(1,3-phenylene)bis(2-oxazoline) (1,3-PBO) as the crosslinking agent. Following the incorporation of the crosslinking structure, the CPI films show good optical transparency (approximately 85% winthin visible light range), enhanced glass transition temperature (from 325 °C to 341 °C), and improved thermal stability, and tensile strength. Notably, compared with the pristine uncrosslinked CPI, these crosslinked CPI films significantly increase in elongation at break (from 5.4% to 44.2%). Furthermore, the new approach ensures that crosslinked CPIs improve heat resistance and mechanical properties, while avoiding the embrittlement of materials. This study also offeres straightforward preparation methods for optically transparent crosslinked polyimides without additional processing steps. All these results make this approach can effectively improve the competitive performance of the CPI films for potential applications in microelectronic and optoelectronic fields.

Nanopore sequencing harnesses changes in ionic current as nucleotides traverse a nanopore, enabling real-time decoding of DNA/RNA sequences. The instruments for the dynamic behavior of substances in the nanopore on the molecular scale are still very limited experimentally. This study employs all-atom molecular dynamics (MD) simulations to explore the impact of charge densities on graphene nanopore in the translocation of single-stranded DNA (ssDNA). We find that the magnitude of graphene’s charge, rather than the charge disparity between ssDNA and graphene, significantly influences ssDNA adsorption and translocation speed. Specifically, high negative charge densities on graphene nanopores are shown to substantially slow down ssDNA translocation, highlighting the importance of hydrodynamic effects and electrostatic repulsions. This indicates translocation is crucial for achieving distinct ionic current blockades, which plays a central role for DNA sequencing accuracy. Our findings suggest that negatively charged graphene nanopores hold considerable potential for optimizing DNA sequencing, marking a critical advancement in this field.

Mechanical properties of polymers can be regulated by changing the numbers of hydrogen bonds and entanglement points. However, the interplay between hydrogen bond network and entangled network during stretching has not been fully studied. We performed molecular dynamics simulations to investigate the changes of hydrogen bonds and entanglements during stretching. The stretching causes the orientation of local segments, leading to the entanglement sliding and disentanglements at different strain regions. Then, the number of entanglement points keeps constant at first and then decreases with increasing strain. Differently, the orientation of local segments can cause the change of chain conformation, which leads to the breakage of hydrogen bonds. Thus, the number of hydrogen bonds decreases with the increase of strain. Simulation results also demonstrated that the number of hydrogen bonds decreases faster during stretching in systems containing more entanglements. In systems with different hydrogen bond site contents, the initial number of entanglement nodes and its decline range during stretching increase firstly and then decrease with the increase of hydrogen bond site content.