Chinese Journal of Polymer Science最新文献

Achieving versatile room temperature phosphorescence (RTP) materials, especially with tunable mechanical properties and shape memory is attractive and essential but rarely reported. Here, a strategy was reported to realize multi-functional RTP films with multicolor fluorescence, ultralong afterglow, adjustable mechanical properties, and shape memory through the synergistic dynamic interaction of lanthanide (Ln^III)-terpyridine coordination, borate ester bonds, and hydrogen bondings in a poly(vinyl alcohol) (PVA) matrix. By varying the amount of borax, the mechanical properties of the films could be finely controlled due to the change of crosslinking degree of dynamic borate ester bonds in PVA. The assembly and disassembly of borate ester bonds upon the trigger of borax and acid were applied as reversible linkage to achieve programmable shape memory behavior. In addition, the films displayed both fascinating multicolor fluorescence and ultralong afterglow characteristics due to the presence of Ln^III doping and confinement of terpyridine in PVA. This study provides a new avenue to impart modulable mechanical strength and shape memory to RTP materials.

Elastomers with high strength and toughness, excellent self-healing properties, and biocompatibility have broad application prospects in wearable electronics and other fields, but preparing it remains a challenge. In this work, we propose a highly adaptable strategy by introducing the small molecule crosslinking agent of triethanolamine (TEA) to the poly thioctic acid (PTA) chains and preparing the PA_xE_y elastomers using a simple synthesis step. This strategy stabilizes the PTA chains by constructing multiple non-covalent cross-linked dynamic networks, endowing materials with excellent strength and toughness (tensile strength of 288 kPa, toughness of 278.2 kJ/m³), admirable self-healing properties (self-healing efficiency of 121.6% within 7 h at 70 °C), and good biocompatibility. The PA_xE_y elastomers can also be combined with MWNTs to become flexible strain sensors, which can be used to monitor human joint movements with high sensitivity, repeatable responses, and stability.

Sulfur-containing dynamic polymers had attracted significant attention due to their unique chemical structures with high reversibility. Utilizating sulfur, an inexpensive industrial waste product, to synthesize dynamic polysulfide polymers through reverse vulcanization has been a notable approach. However, this method required high temperatures and resulted in the release of unpleasant oders. In this study, we presented a robust method for the preparation of sulfur-rich polymers with dynamic polysulfide bonds from elemental sulfur and inexpensive epoxide monomers via a one-pot strategy at the mild room temperature. Different types of polysulfide molecules and polymers were synthesized by reacting various epoxide compounds with sulfur, along with the investigation of their structures and dynamic behaviors. It was noteworthy that the obatined polymers prepared from m-(2,3-epoxypropoxy)-N,N-bis(2,3-epoxypropyl)aniline and elemental sulfur exhibit multiple dynamic behaviors, including polysulfide metathesis and polysulfide-thiol exchange, enabling their rapid stress relaxation, self-healing, reprocessing and degradable properties of the cross-linked polymer. More importantly, the hydroxyl groups at the side chains from epoxide ring opening exhibited potential transesterification. This work provided a facile strategy for designing dynamic sulfur-rich polymers via a mild synthesis route.

The incorporation of molecular switches into polymer networks has been a powerful approach for the development of functional polymer materials that display macroscopic actuation and function enabled directly by molecular changes. However, such materials sometimes require harsh conditions to perform their functions, and the design of new molecular photoswitches that can function under physiological conditions is highly needed. Here, we report the design and synthesis of a spiropyridine-based photoswitchable hydrogel that exhibits light-driven actuation at physiological pH. Owing to its high pK_a, spiropyridine maintains its ring-open protonated form at neutral pH, and the resulting hydrogel remains in a swollen state. Upon irradiation with visible light, the ring closure of spiropyridine leads to a decrease in the charge and a reduction in the volume of the hydrogel. The contracted gel could spontaneously recover to its expanding state in the dark, and this process is highly dynamic and reversible when the light is switched on and off. Furthermore, the hydrogel shows switchable fluorescence in response to visible light. Bending deformation is observed in the hydrogel thin films upon irradiation from one side. Importantly, the independence of this spiropyridine hydrogel from the acidic environment makes it biotolerant and shows excellent biocompatibility. This biocompatible spiropyridine hydrogel might have important biorelated applications in the future.

Poly(butylene adipate-co-terephthalate) (PBAT), a widely studied biodegradable material, has not effectively addressed the problem of plastic waste. Taking into consideration the cost-effectiveness, upcycling PBAT should take precedence over direct composting degradation. The present work adopts a chain breaking-crosslinking strategy, upcycling PBAT into dual covalent adaptable networks (CANs). During the chain-breaking stage, the ammonolysis between PBAT and polyethyleneimine (PEI) established the primary crosslinked network. Subsequently, styrene maleic anhydride copolymer (SMA) reacted with the hydroxyl group, culminating in the formation of dual covalent adaptable networks. In contrast to PBAT, the PBAT-dual-CANs exhibited a notable Young’s modulus of 239 MPa, alongside an inherent resistance to creep and solvents. Owing to catalysis from neighboring carboxyl group and excess hydroxyl groups, the PBAT-dual-CANs exhibited fast stress relaxation. Additionally, they could be recycled through extrusion and hot-press reprocessing, while retaining their biodegradability. This straightforward strategy offers a solution for dealing with plastic waste.

Realizing multiple locked shapes in pre-oriented liquid crystal elastomers (LCEs) is highly desired for diversifying deformations and enhancing multi-functionality. However, conventional LCEs only deform between two shapes for each actuation cycle upon liquid crystal-isotropic phase transitions induced by external stimuli. Here, we propose to regulate the actuation modes and the locked shapes of a pre-orientated epoxy LCE by combining dynamic covalent bonds with cooling-rate-mediated control. The actuation modes can be adjusted on demand by exchange reactions of dynamic covalent bonds. Derived from the established actuation modes, such as elongation, bending, and spiraling, the epoxy LCE displays varied locked shapes at room temperature under different cooling rates. Various mediums are utilized to control the cooling rate, including water, silicone oil, and copper plates. This approach provides a novel way for regulating the actuation modes and locked shapes of cutting-edge intelligent devices.

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.