Journal of Polymer Science最新文献

Polyvinylidene fluoride (PVDF), a semicrystalline polymeric material, exhibits five crystalline phases (α, β, γ, δ, and ε), with its crystalline structure altered under different fabrication conditions. This work systematically investigates the effects of extrusion temperature (190°C–210°C) and screw rotation speed (30–110 rpm) on the crystalline phases, crystallinity, and thermal stability of PVDF, while also exploring the recrystallization behavior of PVDF during solution casting. The results demonstrate that melt extrusion can convert PVDF crystal forms from the α-phase to the β-phase, increasing the β-phase fraction to 75.69%–81.94%. The screw rotation speed is the primary cause of this variation. Under different processing conditions, the crystallinity of PVDF is increased by 0.93%–6.10%, and the decomposition temperature is improved by approximately 20°C through melt extrusion. For the solution casting process, it causes a β-phase to γ-phase transition in PVDF, achieving γ-phase fractions of 66.23%–74.74%, with the crystallinity values of 51.05%–56.58%.

This work reports a bio-based polybenzoxazine vitrimer that simultaneously achieves high glass transition temperature (T _g), excellent reprocessability, and outstanding chemical resistance. The synthesis involves first esterifying phloretic acid with tyrosol to form bisphenol ester (BPE), which then undergoes Mannich condensation to yield the benzoxazine monomer, finally polymerized via ring-opening to afford ester-containing polybenzoxazine vitrimer (PEBZ). Because of the dynamic transesterification reactions (TERs), PEBZ has processable performance. The tensile strength retention rates of PEBZ after three times reprocessing were 90.4%, 72.1%, and 57.0%. PEBZ also has excellent thermal performance. The T _g is as high as 217°C, and its thermal decomposition temperatures T _d5 and T _d10 are 338°C and 369°C, respectively, with a carbon yield of 40.3%. These thermal characteristics remain basically unchanged after three post-treatment cycles. Due to the high crosslinking density and rigid framework of benzoxazine, PEBZ has excellent chemical resistance. This polybenzoxazine vitrimer achieves a unity of high performance and recyclability, providing a broader range of application scenarios for processable materials.

This study presents a novel, systematic approach to developing lightweight, flexible microwave absorbing composites based on styrene–butadiene–styrene (SBS) filled with conductive and magnetic fillers. Graphite and nickel powders were combined to simultaneously introduce dielectric and magnetic loss mechanisms, allowing their combined effect to enhance microwave absorption, while a physical blowing agent created microcellular foam at two target densities (0.6 and 0.44 g cm⁻³) to evaluate porosity effects. Systematic variation of filler ratios and foam morphology enabled tuning of dielectric–magnetic interactions and impedance matching. Scanning electron microscopy showed nickel addition affected graphite dispersion, and higher blowing agent content produced finer, more uniform cells; dielectric and magnetic characterization revealed enhanced permittivity and magnetic permeability from interfacial polarization and magnetic dipolar effects, especially in the optimal 40 phr graphite/40 phr nickel formulation. This composite showed a minimum reflection loss (RL_min) of −18 dB and an effective absorption bandwidth of 9.71–12.50 GHz (~2.79 GHz) (at ~0.6 mm), outperforming the graphite-only composite with 40 phr filler, which exhibited only a narrow window near 8–9 GHz (~1.0 GHz). Further enhancement was achieved with the foamed version at 0.44 g cm⁻³, where the finer, more homogeneous cellular morphology yielded RL_min = −54 dB (10.49 GHz) and broadband coverage across the X-band (8.0–12.5 GHz) at ~0.8 mm.

We report the preparation of chemically crosslinked alginate gels (ChemAlg_ss) using cystamine as a disulfide-containing crosslinker, along with dual crosslinked gels (DualAlg_ss) by further treating with CaCl₂. Gelation occurred when cystamine was used at 5–80 mol%, wherein the highest crosslinking density was achieved at 40 mol%. Rheological studies revealed that the storage modulus of DualAlg_ss was larger than that of ChemAlg_ss, reflecting the enhanced formation of physical crosslinking. Moreover, ChemAlg_ss exhibited reversible sol–gel transitions by the treatment with dithiothreitol (c = 380 mM) and subsequent addition of 30 wt% of hydrogen peroxide aqueous solution. These findings demonstrate a simple strategy for designing redox-responsive alginate hydrogels.

A phosphorus–nitrogen hybrid flame retardant (L–CS–P₂O₅) was developed using a two-stage synthesis method, based on lignin, chitosan, and phosphorus pentoxide as the main components. It was then incorporated into thermoplastic polyurethane (TPU) to enhance its flame-retardant properties. The performance under different additions was investigated. Data indicated that adding 15 phr of L–CS–P₂O₅ to TPU composite materials was the optimal ratio for achieving flame retardancy. At this ratio, the TPU/15 phr L–CS–P₂O₅ mixture exhibited excellent flame retardancy, with a limiting oxygen index of 24.6% and V-2 rating in the UL-94 test. Compared with pure TPU, the addition of 15 phr of L–CS–P₂O₅ significantly reduced the peak heat release rate (PHRR) and peak smoke production rate (PSPR) by 63.26% and 64.62%, respectively. The impressive flame-retardant performance stemmed from a powerful synergy between condensed and gas-phase mechanisms, combining processes like dehydration, char formation, dilution of flammable gases, and free radical quenching effects. In addition, the incorporation of L–CS–P₂O₅ induced a plasticizing effect in TPU, resulting in a 45.32% enhancement in elongation at break. This significant mechanical improvement substantially broadened the potential application scope of TPU composites in more fields.

As a high-performance melt-processable fluoropolymer, perfluoroalkoxy (PFA) exhibits mechanical properties that are critically influenced by its crystalline structure. However, capturing detailed insights into the crystallization process of PFA proves challenging due to its exceptionally rapid crystal growth rate. In this paper, the crystallization kinetics and structural reorganization of PFA across three distinct anneal regimes: sub-melting (280°C–305°C), self-nucleation (305°C–320°C), and complete melting (> 320°C) were dynamically examined via utilizing multi-scaled analytical approaches such as differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarized optical microscopy (POM), etc. The results demonstrate that annealing in the sub-melting region significantly improves both crystallinity (by up to 33%) and lamellar thickness (by up to 23.7%), owing to molecular chain rearrangement and crystal perfection. Within the self-nucleation region, annealing induces partial melting and subsequent recrystallization, resulting in a homogeneous lamellar distribution and optimized mechanical performance. However, annealing in the complete melting region erases the crystal memory effect, yielding a regenerated crystalline architecture with short-range order similar to that of the untreated sample. These insights bridge laboratory analysis with industrial processing, enabling precise microstructure control for manufacturing high-reliability PFA components in electronic and power transmission applications.

Given the increasing depletion of petrochemical resources and the intensification of environmental issues, the development of high-performance bio-based functional materials is crucial for achieving sustainable development. This study utilized renewable rosin as the raw material. Rosin-based ester was prepared through an esterification reaction with glycidyl methacrylate, which was subsequently reacted with diisocyanate of different structures (aromatic/alicyclic) to synthesize a series of rosin-based polyurea materials containing dynamic urea bonds. The influence of diisocyanate type on the material properties was systematically investigated. The results indicate that polyurea constructed from alicyclic diisocyanate exhibited superior comprehensive performance. Benefiting from the synergistic reversible effects of the dynamic urea bonds and hydrogen bonds within the material, the resulting materials not only demonstrate good mechanical properties (tensile strength reaching 4.29 MPa) but also possess excellent self-healing capabilities (scratches could be completely repaired within 6 h at 100°C). Additionally, these materials combine good thermal stability with coating performance. This study provides an effective strategy for developing self-healing bio-based polymeric materials.

An improved synthetic strategy for pyrrolo[3,4-b]dithieno[2,3-f:2′-h]quinoxalindione derivatives was developed as acceptor units in donor-acceptor (D-A) polymers for organic solar cells. The approach involves the efficient fusion of two pendant thienyl groups in 6-(2-octyldodecyl)-2,3-di(thiophen-3-yl)-5H-pyrrolo[3,4-b]pyrazine-5,7(6H)-dione into a dithienoquinoxaline skeleton via FeCl₃-mediated oxidative coupling, achieving excellent yields. Compared to previous methods, this route demonstrated higher yields, shorter reaction times, and simplified purification processes. Two polymers, PQB and PQDB, synthesized from the monomer and BDT-Cl, exhibited high thermal stability with decomposition temperatures of 400.52°C and 420.37°C, respectively. Their absorption maxima were 468 and 464 nm in solution, and 467 and 485 nm as films, with optical bandgaps of 1.90 and 1.85 eV. HOMO energy levels were calculated as −5.82 and −5.64 eV, and LUMO energy levels as −3.56 and −3.50 eV, respectively. The HOMO energy levels are among the lowest observed, presenting a new avenue for a distinct class of wide-band polymers. Optimized solar cells based on PQDB and PCBM, fabricated with 1 vol% DIO and without annealing, achieved a power conversion efficiency (PCE) of 3.18%.