Chinese Journal of Polymer Science最新文献

Nuclear magnetic resonance (NMR) is an advanced technique for the molecular weight (MW) determination of polymers at quantitative conditions. In this study, we investigate the effect of liquid ¹H-NMR instrumental setting parameters on the MW determination of polyether diols, namely poly(ethylene glycol) (PEG) and poly(tetramethylene oxide) (PTMO) diols, using hydroxymethylene groups as chain-ends. Our results show that the protons in chain-ends have larger spin-lattice relaxation time (T₁) than those in main chains. To let most of the excited protons relax to the equilibrium state, the delay time (d₁) should be much larger than T₁ of end-groups. When ¹³C decoupling is inactive, the relative errors can be greater than 60%, due to the ¹³C-coupled proton satellite peaks, which can overlap with chain-end groups or be misassigned as chain-ends. The optimal quantitative NMR conditions for the MW estimation of polyethers are revealed below: standard pulse with inverted gated ¹³C decoupling pulse sequence, 32 scans, 2.0 s acquisition time in 90 degree of flip angle and 30 s d₁. The MWs determined from ¹H quantitative NMR are all smaller than those from SEC which are relative to polystyrene (PS) standards, since the size of polyether chains is larger than that of PS with the same MW. In addition, the MW obtained from SEC for PTMOs shows larger overestimation than PEGs, suggesting PEG chains are more flexible than PTMO’s.

A series of novel side-chain liquid crystalline (SCLC) copolymers were synthesized by attaching two distinct mesogenic units, namely a chiral cholesteryl-based monomer (M1) and an achiral biphenyl-based monomer (M2), to a poly(3-mercaptopropylmethylsiloxane) (PMMS) backbone via thiol-ene click chemistry. The influence of side chain composition on the self-assembly behavior and phase structures of these SCLC copolymers was systematically investigated using different instrument. Results indicate that three distinct liquid crystalline phases and four unique molecular configurations were identified within the polymer series, with the emergence of the liquid crystalline phase being a synergistic outcome of the two distinct side chains. This study underscores the critical influence of side chain dimensions, rigidity, and spatial volume on the self-assembly structures and phase characteristics of liquid crystalline polymers, providing valuable insights for the rational design and development of advanced functional materials with tailored properties.

Epoxy resins are cross-linked polymeric materials with typically low thermal conductivity. Currently, the introduction of rigid groups into epoxy resins is the main method to improve their intrinsic thermal conductivity. The researchers explored the relationship between the flexible chains of epoxy monomers and the thermal conductivity of the modified epoxy resins (MEP). The effect of flexible chain length on the introduction of rigid groups into the cross-linked structure of epoxy is worth investigating, which is of great significance for the improvement of thermal conductivity of polymers and related theories. We prepared a small molecule liquid crystal (SMLC) containing a long flexible chain via a simple synthesis reaction, and introduced rigid mesocrystalline units into the epoxy resin via a curing reaction. During high-temperature curing, the introduced mesocrystalline units underwent orientational stacking and were immobilized within the polymer. XRD and TGA tests showed that the ordering within the modified epoxy resin was increased, which improved the thermal conductivity of the epoxy resin. Crucially, during the above process, the flexible chains of SMLC provide space for the biphenyl groups to align and therefore affect the thermal conductivity of the MEP. Specifically, the MEP-VI cured with SMLC-VI containing six carbon atoms in the flexible chain has the highest thermal conductivity of 0.40 W·m⁻¹·K⁻¹, which is 125% of the thermal conductivity of SMLC-IV of 0.32 W·m⁻¹·K⁻¹, 111% of the thermal conductivity of SMLC-VIII of 0.36 W·m⁻¹·K⁻¹, and 182% of the thermal conductivity of pure epoxy of 0.22 W·m⁻¹·K⁻¹. The introduction of appropriate length flexible chains for SMLC promotes the stacking of rigid groups within the resin while reducing the occurrence of chain folding. This study will provide new ideas for the enhancement of thermal conductivity of cross-linked polymeric materials.

Silicon-containing arylacetylene (PSA) resins have broad application prospects because of their excellent heat resistance. However, improving their mechanical properties and interfacial bonding with reinforcement fibers while maintaining heat resistance is a challenge in engineering applications. Here, poly(diethynylbenzene-methylsilyl-3-benzonitrile) (DEB-CN) and poly(diethynylbenzene-methylsilyl-3,6-diethynylcarbazole-3-benzonitrile) (DEC-CN) were synthesized via an isopropylmagnesium chloride lithium-chloride complex (i-PrMgCl·LiCl), overcoming the compatibility problem between cyano groups and Grignard reagents. The cyano and alkyne groups in the resin underwent cyclization to form pyridine, catalyzed by the -NH- moiety in DEC-CN, resulting in extremely high thermal stability (5% weight loss temperature: 669.3 °C, glass transition temperature >650 °C). The combination of cyano dipole-dipole pairing and hydrogen bonding greatly enhanced the resin-fiber interface properties, while the generated pyridine promoted stress relief in the crosslinked network, substantially improving the mechanical properties of the cyano-silicon-containing arylacetylene resin composites. The flexural strength of quartz fiber cloth/DEC-CN composites was 298.2 MPa at room temperature and 145.9 MPa at 500 °C, corresponding to 84.0% and 127.6% enhancements, respectively, over the cyano-free counterpart. These cyano-silicon-containing arylacetylene resins exhibited a dual reinforcement mechanism involving physical interfacial interactions and chemical crosslinking, achieving a good balance between thermal stability and mechanical properties.

Using molecular dynamics (MD) simulations, this study explores the fluid properties of three polymer melts with the same number of entanglements, Z, achieved by adjusting the entanglement length N_e, while investigating the evolution of polymer melt conformation and entanglement under high-rate elongational flow. The identification of a master curve indicates consistent normalized linear viscoelastic behavior. Surprising findings regarding the steady-state viscosity at various elongational rates (Wi_R>4.7) for polymer melts with the same Z have been uncovered, challenging existing tube models. Nevertheless, the study demonstrates the potential for normalizing the steady-state elongational viscosity at high rates (Wi_R>4.7) by scaling with the square of the chain contour length. Additionally, the observed independence of viscosity on the elongational rate at high rates suggests that higher rates lead to a more significant alignment of polymer chains, a decrease in entanglement, and a stretching in contour length of polymer chains. Molecular-level tracking of tagged chains further supports the assumption of no entanglement under rapid elongation, emphasizing the need for further research on disentanglement in polymer melts subjected to high-rate elongational flow. These results carry significant implications for understanding and predicting the behavior of polymer melts under high-rate elongational flow conditions.

As a type of bi-functional device, electrochromic supercapacitors (EC-SCs) have attracted extensive attention in diverse applications such as flexible electronics. However, despite recent encouraging progress, rational design and development of high-performance EC-SC materials with desirable stability remain challenging for practical applications. Here, we propose a fluorination strategy to develop high-performance EC-SC materials with tough hydrogen bonding cross-linked intermolecular polymer network by one-step electrosynthesis of 3-fluorothiophene. The electrosynthesized free-standing poly(3-fluorothiophene) (PFT) films simultaneously achieve high electrochromic performance (optical contrast 42% at 560 nm with reversible color changes between purple and blue), and good capacitance property (290 F·g⁻¹, 1 A·g⁻¹), as well as outstanding cyclic stability (<2% reduction after 20000 cycles). We further demonstrate the fabrication of PFT-based flexible electrochromic supercapacitor devices (FESDs), and the resultant devices can be used to visually monitor the energy storage state in real-time and maintain outstanding stability under mechanical distortion like bending. Such a tough fluorination hydrogen bonding cross-linking strategy may provide a new design concept for high-performance EC-SC materials and reliable FESDs toward practical applications.

This study utilizes molecular dynamics simulation to investigate the complex dynamics of entangled semi-flexible polymer melts. The investigation reveals a significant stress overshoot phenomenon in the systems, demonstrating the intricate interplay between shear rates, chain orientation, and chain stretching dynamics. Additionally, the identification of metastable states, characterized by a dual-plateau phenomenon in the shear stress-strain curve at specific Rouse-Weissenberg number Wi_R, showcases the system’s responsiveness to external perturbations and its transition to stable shear banding states. Moreover, the analysis of flow field deviations uncovers a progression of shear bands with increasing Wi_R, displaying distinct behaviors in the system’s dynamics under different shear rates and chain lengths. These findings challenge established theoretical frameworks and advocate for refined modelling approaches in polymer rheology research.

Supramolecular polymer networks (SPNs) are celebrated for their dynamic nature, yet they often exhibit inadequate mechanical properties. Thus far, the quest to bolster the mechanical resilience of SPNs while preserving their dynamic character presents a formidable challenge. Herein, we introduce [2]rotaxane into SPN to serve as another cross-link, which could effectively enhance the mechanical robustness of the polymer network without losing the dynamic properties. Compared with SPN, the dually cross-linked network (DPN) demonstrates superior breaking strength, Young’s modulus, puncture force and toughness, underscoring its superior robustness. Furthermore, the cyclic tensile tests reveal that the energy dissipation capacity of DPN rivals, and in some cases surpasses, that of SPN, owing to the efficient energy dissipation pathway facilitated by [2]rotaxane. In addition, benefiting from stable topological structure of [2]rotaxane, DPN exhibits accelerated recovery from deformation, indicating superior elasticity compared to SPN. This strategy elevates the performance of SPNs across multiple metrics, presenting a promising avenue for the development of high-performance dynamic materials.

Amyloidosis is characterized by the deposition of fibrillar aggregates, with a specific peptide or protein as the primary component, in affected tissues or organs. Excessive proliferation and deposition of amyloid fibrils can cause organismal dysfunction and lethal pathological outcomes associated with amyloidosis. In this study, a nanochaperone (nChap-NA) was developed to inhibit protein misfolding and fibrillation by simulating the function of natural molecular chaperones. The nanochaperone was prepared by self-assembly of two block copolymers PEG-b-PCL and PCL-b-P(NIPAM-co-AANTA), which had a phase-separated surface consisting of hydrophobic PNIPAM microdomains with coordinative NTA(Zn) moieties and hydrophilic PEG chains. The hydrophobic interaction of the PNIPAM microdomain and the coordination of NTA(Zn) synergistically work together to effectively trap the amyloid monomer and block its fibrillation site. Insulin and human islet amyloid polypeptide (hIAPP) were used as model proteins to investigate the nanochaperone’s inhibition of amyloid misfolding and fibrillation. It was proved that the nanochaperone could stabilize the natural conformation of the trapped insulin and hIAPP, and effectively inhibit their fibrillation. In vivo study demonstrated that the nanochaperone could effectively preserve the bioactivity of insulin and reduce the cytotoxicity caused by hIAPP aggregation. This study may provide a promising strategy for the prophylactic treatment of amyloidosis.

Polyethyleneimine (PEI), as a widely used polymer material in the field of gene delivery, has been extensively studied for modification and shielding to reduce its cytotoxicity. However, research aimed at preparing degradable PEI is scarce. In this work, the hydrogen peroxide (H₂O₂) oxidation method was used to introduce degradable amide groups in the PEI and a series of oxidized PEI22k (oxPEI22k) with different degrees of oxidation were synthesized by regulating the dosage of H₂O₂. The relationship between the oxidation degree of oxPEI22k and the gene transfection efficiency of oxPEI22k was studied in detail, confirming that the oxPEI22k with oxidation degrees of 16.7% and 28.6% achieved improved transfection efficiency compared to unmodified PEI. These oxPEI22k also proved reduced cytotoxicity and improved degradability. Further, this strategy was extended to the synthesis of low-molecular-weight oxPEI1.8k. The oxPEI1.8k with suitable oxidation degree also achieved improved transfection efficiency and reduced cytotoxicity. In brief, this work provided high-efficiency and low-cytotoxicity degradable gene delivery carriers by regulating the oxidation degree of PEI, which was of great significance for promoting clinical applications of PEI.