Chinese Journal of Polymer Science最新文献

Recycling of carbon fiber reinforced composites is important for sustainable development and the circular economy. Despite the use of dynamic chemistry, developing high-strength recyclable CFRPs remains a major challenge due to the mutual exclusivity between the dynamic and mechanical properties of materials. Here, we developed a high-strength recyclable epoxy resin (HREP) based on dynamic dithioacetal covalent adaptive network using diglycidyl ether bisphenol A (DGEBA), pentaerythritol tetra(3-mercapto-propionate) (PETMP), and vanillin epoxy resin (VEPR). At high temperatures, the exchange reaction of thermally activated dithioacetals accelerated the rearrangement of the network, giving it significant reprocessing ability. Moreover, HREP exhibited excellent solvent resistance due to the increased cross-linking density. Using this high-strength recyclable epoxy resin as the matrix and carbon fiber modified with hyperbranched ionic liquids (HBP-AMIM⁺PF₆⁻) as the reinforcing agent, high performance CFRPs were successfully prepared. The tensile strength, interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of the optimized formulation (HREP20/CF-HBPPF₆) were 1016.1, 70.8 and 76.0 MPa, respectively. In addition, the CFRPs demonstrated excellent solvent and acid/alkali-resistance. The CFRPs could completely degrade within 24 h in DMSO at 140 °C, and the recycled CF still maintained the same tensile strength and ILSS as the original after multiple degradation cycles.

Vitrimers have emerged as a prominent research area in the field of polymer materials. Most of the studies have focused on synthesizing polymers with versatile dynamic crosslinking structures, while the impact of chemical structure on aggregate structure of vitrimers, particularly during polymer processing, remains insufficiently investigated. The present study employed commercial maleic anhydride-grafted-high density polyethylene (M-g-HDPE) as the matrix and hexanediol as the crosslinker to facilely obtain fiber-shaped HDPE vitrimers through a reaction extrusion and post-drawing process. Through chemical structure characterization, morphology observation, thermal and mechanical properties investigation, as well as aggregate structure analysis, this work revealed the influence of dynamic bonds on the formation of aggregate structures during fiber-shaped vitrimers processing. A small amount of dynamic bonds in HDPE restricts the motion of PE chain during melt-extruding and post-drawing, resulting in a lower orientation of the PE chains. However, lamellar growth and fibril formation during post-drawing at high temperature are enhanced to some extent due to the competition between dynamic bond and chain relaxation. The uneven morphology of fiber-shaped HDPE vitrimers can be attributed to the stronger elastic effect brought by dynamic bonding, which plays a more dominant role in determining the mechanical properties of fiber-shaped vitrimers compared to aggregate structure.

Polymer aging under environmental conditions causes deterioration of service properties. Understanding the aging behavior and mechanism is important not only for lifetime prediction, but also for material improvement and development. Therefore, comprehensive characterization of polymer materials during aging is crucial. In this review, various analytical methods for characterization of chemical changes, physical changes and service properties are introduced. Based on that, methods for stabilization evaluation and lifetime prediction, especially sensitive evaluation methods are reviewed. Chemical changes include molecular weight changes by chain scission and crosslinking, functional group changes on the surface and in the bulk, formation of free radicals, formation of small molecular species as the degradation products, and chemical distribution by heterogeneous aging and additives migration. Physical changes include crystallization changes (post- or chemi-crystallization) and morphology changes (cracking, debonding, etc.). Service property changes include deterioration of processability, mechanical properties, electrical properties and appearance. In the end, existing problems and future research perspective are proposed, including relationship between chemical/physical changes and service properties, introduction of modern mathematical and computer tools.

The crystallization behavior of silica-filled polydimethylsiloxane (PDMS) was investigated in detail by ¹H solid-state nuclear magnetic resonance (¹H SS-NMR) in combination with synchrotron radiation wide-angle X-ray scattering (WAXS), and temperature-modulated differential scanning calorimetry (TMDSC) techniques. For neat PDMS, no apparent difference is observed for the crystallinity characterized by ¹H SS-NMR and WAXS at low-temperature regions. However, upon filler addition, a 15%–35% lower difference in crystallinity is observed measured by ¹H SS-NMR compared to WAXS. The origin of such mismatch was explored through multi-component structural, dynamics, and chain-order analysis of PDMS samples with different filler fractions. The 1D integrated WAXS results of PDMS with different filler fractions at different temperatures show that the packing structure as well as crystal size basically remain unchanged, but as the filler fraction increases from 0 phr to 60 phr, the rigid component’s dynamics order parameter S_r obtained by ¹H SS-NMR decreases from 0.70 to 0.55. The filler fraction-dependent crystallinity calculated based on S_r was compared with experimental values, revealing a behavior of decreasing order in the crystalline region. Combining with the results of accelerated chain dynamics in crystalline region as reflected by T₂ values, the molecular origin is attributed to the formation of CONDIS crystals, whose conformational order is lost but the position and orientation orders are kept. Such hypothesis is further supported by the TMDSC results, where, as the filler fraction increases from 0 phr to 60 phr, the melting range widens from 8.77 K to 14.56 K, representing a growth of 166%. In addition to previous reports related to the condition for forming CONDIS mesophase, i.e., temperature, pressure, and stretching, the nano-sized filler could also introduce the local conformational disorder for chain packing.

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.

Nonconventional luminescent materials (NLMs) are a type of organic luminescent materials that does not contain aromatic units. Due to the simplicity of the synthesis process, mild reaction conditions, good hydrophilicity and biological compatibility, NLMs have attracted much attention. Nevertheless, numerous reports indicate that NLMs can only effectively luminesce at high concentrations and in solid state, which limits their applicability in the field of cell imaging. This study addresses this limitation by designing and synthesizing oligomers P1, P2 and P3 using ethylene glycol diglycidyl ether and amine compounds containing ethylene groups. These oligomers exhibit remarkable luminescence efficiency reaching as high as 9.2% in dilute solutions (0.1 mg/mL), making them among the best NLMs in this category. Furthermore, the synthesized oligomers exhibit excitation wavelength-dependent and concentration-dependent luminescence intensity, fluorescence response to temperature and pH changes, as well as the ability to identify Fe³⁺, Cu²⁺ and Mo⁵⁺ in dilute solutions. These characteristics render them potentially useful in the for cell imaging.

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.

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.