Chinese Journal of Polymer Science最新文献

Viscoelastic properties of thermoplastic polyurethane (TPU) is of fundamental importance for its processing. In this work, we prepared different TPUs from polycaprolactone (PCL) diol, diphenylmethane-4,4′-diisocyanate (MDI), and 1,4-butanediol (BDO), and investigated the viscoelastic behavior of three TPUs with different hard segment content during thermal annealing process. The storage modulus (G′) of TPU increases over time in a medium annealing temperature (T_a) region, but remains unchanged at both high and low temperature regions. The growth of loss modulus (G″) over time is slower than that of G′. At medium T_a, both G′ and G″ increase during the repeating frequency (ω) sweep, due to the gradual crystallization of hard segments. This indicates that the crystallites primarily restrain the relaxation of unit with large size. The increments of G′ and G″ are weakened when the content of hard segment in TPU is decreased. For TPU with high content of hard segments, a complete high elastic platform with a width of 3 orders of magnitude was observed only through one frequency scan test at medium T_a. In addition, the crystallites of hard segments grow up continuously during frequency scan test (isothermal annealing treatment) and cause the extreme increase in G′ and G″ with ω in low ω region.

Membrane fusion is essential for many cellular physiological functions, which is modulated by highly precise molecular mechanism involving multiple energy barriers. Nanoparticles (NPs), which exhibit immense potential in the field of biomedical applications, can act as fusogen proteins to initiate and regulate membrane fusion. However, the underlying mechanisms of NP-induced membrane fusion and the molecular details involved remain largely elusive. Here, using coarse-grained molecular dynamics simulations, we systematically investigate the NP-induced membrane fusion behaviors and the influences of NP properties (size, hydrophobicity and hydrophilicity). Our results show that the vesicle-bilayer fusion induced by a hydrophobic NP is an intricately state-wise process, involving the approach and local deformation of the vesicle and bilayer bridging by the NP, the flip-flop of lipids from proximal leaflets and the formation of a fusion stalk, as well as further lipid interactions between distal leaflets and complete fusion. Moreover, we find that NP properties have distinct effects on membrane fusion and thus the optimal NP conditions for facilitating membrane fusion are obtained. Our work provides a mechanistic understanding of NP-induced membrane fusion and offers useful insights for efficient and controlled regulation of membrane fusion.

Star-shaped poly(lactic acid)s (PLAs) with two to five arms were synthesized by ring opening polymerization using tin(II) 2-ethylhexanoate as catalyst and polyols as initiators. The effects of molecular weight together with multi-arm architecture on crystallization behavior, spherulite morphology and alkaline degradation behavior of star-shaped PLAs have been investigated. The results indicate that the multi-arm architecture interfered with spherulite growth, but promoted nucleation and alkaline degradation of star-shaped PLAs. Interestingly, with the increase of molecular weight (M_n), the crystallization rate first increased and then decreased, while the alkaline degradation rate was the opposite. The characteristic crystallization and alkaline degradation behavior of star-shaped PLAs were discussed based on the competition between segmental mobility and central core confinement.

Anion-exchange membranes (AEMs) with high conductivity and stability are essential components of hydrogen related water electrolysis and fuel cell applications. During the past decades, polynorbornene (PNB)-based AEMs have shown excellent performance due to their saturated all-carbon-based backbones and diverse strategies to prepare cross-linked membranes. However, nearly all previously reported PNB-based AEMs rely on the alkyl-substituted norbornene monomers, whose low-yielding synthesis leads to high-cost of the AEMs. In addition, the cross-linked PNB-based AEMs usually suffered from mechanical brittleness. Herein, we propose a novel semi-interpenetrating polymer network (s-IPN) strategy to simultaneously enhance mechanical modulus and ionic conductivity, while using commercial 5-vinyl-2-norbornene (VNB) as the single norbornene derivatives to prepare high-performance AEMs. A diallylphenol quaternary ammonium salt was used for photo-induced cross-linking with poly-VNB and various dithiols to produce AEMs with s-IPN structures. The resultant membranes have excellent hydroxide conductivities and alkaline stability in 1 mol/L KOH at 80 °C, and are successfully applied in alkaline anion-exchange membrane water electrolyzers to stably operate for over 150 h.

The present study presents an assessment of the interrelations between long-chain branching, specific nucleation, and end-use properties of polypropylene blends: blends of linear polypropylene (L-PP) and long-chain branched polypropylene (LCB-PP) modified by a specific β-nucleating agent (NA). Specimens with various LCB-PP compositions with and without NA were prepared under complex flow fields by injection molding. Wide-angle X-ray scattering was employed to capture the X-ray patterns of both the skin and core of the specimens, determining the overall crystallinity and amounts of individual polymorphs. The increasing content of LCB-PP and γ-phase, at the same time, in the blends is reflected in both increasing crystallinity and improved mechanical properties, namely, yield stress and Young’s modulus. On the other hand, the composition of the blends had no significant effect on the impact strength, except for nucleated L-PP. It has been demonstrated that adding a relatively small amount of LCB-PP is sufficient to modify the mechanical properties of linear polypropylene. Even a very small amount of LCB-PP in the L-PP suppressed the effectiveness of NA.

Conjugated polymers are mainly synthesized by cross-coupling polymerizations catalyzed with transition metal (Pd, Ni) catalysts through step-growth polymerization (SGP) mechanism. According to the classical theory of SGP, the polymer dispersion index (Ð) of the synthesized polymers will never be higher than 2. However, the cases where conjugated polymers synthesized with Ð value far exceeding 2 are very common in reality, which severely limits their processing property, performance and applications. To investigate the reason behind the Ð value deviation from the theoretical value of SGP, direct arylation polycondensation (DArP) of 2-bromo-3-hexylthiophene (3HT) was chosen as the model reaction, and the reaction process was tracked using gel permeation chromatography analysis. When Pd(OAc)₂ was used as the catalyst, the Ð value linearly increased with the increase of the weight-average molecular weight (M_w) of polymer (P3HT) after a short period and reached up to 7.2 at prolonged reaction time. Scanning transmission electron microscopic images of the reaction mixture showed the fibril-like aggregation of P3HT and assembling of Pd species in P3HT aggregates. A catalyst competition mechanism was thus proposed, together with numerical calculation, giving a good fitting to the experimental results, which is believed to have far-reaching significance for guiding the design, synthesis and processing of conjugated polymers.

Photonic materials, which react to light, have garnered interest due to their capability to exhibit adjustable structural colors. Typically, light targets the UV, visible, or near-IR spectrums. In this study, microgel-based photonic materials that are capable of reversibly responding to X-rays have been engineered. To accomplish this, azobenzene (Azo)-containing poly(N-isopropylacrylamide) (pNIPAm)-based microgels are synthesized. Subsequently, ZnS scintillator and Cr/Au are applied on each side of the poly(methyl methacrylate (PMMA) substrate. Subsequently, the Azo MG monolayer is deposited onto the Au surface, followed by the deposition of an additional layer of Cr/Au. This process generates ZnS/PMMA/Cr/Au/Azo MG/Cr/Au or ZnS/Au-Azo MG-Au structure. Functioning as a typical interferometer, ZnS/Au-Azo MG-Au demonstrates tunable colors based on the separation distance between the two Au layers. The ZnS scintillator can absorb and convert X-rays into UV light, initiating the transition of the Azo groups from a trans to a cis state. Consequently, this transition causes the Azo MG to swell. As Azo MG swells, the distance between the two Au layers increases, resulting in a red-shift of approximately 350 nm in the optical signal of the ZnS/Au-Azo MG-Au interferometer. Remarkably, this X-ray responsivity of the interferometer is reversible, as it returns to its initial state after being stored in the dark for 24 h. To demonstrate its capabilities, the ZnS/Au-Azo MG-Au interferometer successfully releases a drug when triggered by X-ray stimulation, thus validating its potential. The microgel-based interferometers hold significant promise for applications in chemoradiotherapy, radiobiology, and actuators in space.

Copolyfluorenes are of great interest due to their ability to form thin films with tunable optical and electrical properties. In this paper, copolymers of polyfluorene with electron withdrawing dicyanostilbene and dicyanophenanthrene moieties were synthesized; their thin films were characterized by electron spectroscopy, cyclic voltammetry, electrical, and photoelectrical measurements. The mobility of charge carriers in the copolymers was measured for the first time, with the acceptor components providing balanced electron and hole mobilities of the order of 10⁻⁶ cm²·V⁻¹·s⁻¹. Photodetectors based on the copolymer/PTCDI heterojunction exhibited the photoresponse band extended into the green region due to the absorption of PTCDI and an increased photocurrent in the UV-blue absorption band of the copolymer, which is related to the absorption of photoluminescent emission of the copolymers in PTCDI. The presented approach to improving the performance of a polymer-based photodetector is promising in organic optoelectronics.

In particle-filled polymer composites with selective distributions of fillers in one phase, much attention has been focused on the “volume exclusion effect” in reducing the percolation threshold of filler, while the role of dispersed polymer phase acting as bridges of fillers in the particle network has largely been ignored. Herein, we studied industrially important ternary composites, polypropylene (PP)/ethylene-octene copolymer (a polyolefin elastomer, POE)/talc systems, and adopted rheology to reveal the bridging behavior of POE droplets in the network of talc particles. It is found that talc fillers concentrate in the PP phase using the “blend first” protocol, while more talc particles are located at the interface of PP and POE phases using the “filler first” protocol. Changing the POE viscosity and talc size can affect the migration of talc from the POE phase to the PP phase in the “filler first” protocol. The linear rheology behavior indicates that besides the “volume exclusion effect”, the talc-POE hybrid network can further contribute to the reinforcement effect. Meanwhile, the POE droplet bridging structure can facilitate the rebuilding of the hybrid network after large amplitude oscillatory shear, in contrast to the un-recoverable structures in the PP/talc binary composites. The correlation between rheology and selective distribution of fillers in ternary composites may provide practical guidance for processing and designing advanced polymer composites with controlled selective location of fillers.

This study delves into the pivotal role of sulfur vulcanization in defining the mechanical characteristics of natural rubber (NR) latex-dipped products. Utilizing sulfur vulcanization, known for its operational simplicity and cost-effectiveness, we examine its ability to enhance product elasticity and mechanical strength through various sulfidic bond formations such as mono-, di-, and polysulfidic bonds. Different vulcanization systems and sulfur contents were evaluated for their influence on the mechanical attributes of latex films, employing three types of NR latex, namely concentrated NR (CNR), deproteinized NR (DPNR), and small rubber particle NR (SRP), each representing distinct non-rubber components (NRCs). The study utilized advanced atomic force microscopy (AFM) equipped with PeakForce Quantitative Nanomechanical Mapping (QNM) to visualize and measure Young’s modulus distribution across the film of pre-vulcanized latex. Our findings reveal that films by CNR processed using the conventional vulcanization (CV) system exhibited enhanced tensile strength and elongation at break. It even showed a lower crosslink density than those processed using the efficient vulcanization (EV) system. Interestingly, DPNR films showed a more uniform distribution of Young’s modulus, correlating well with their superior mechanical strength. In contrast, SRP films showed excessive network structure formation in the particles due to accelerated vulcanization rates, hampering subsequent post-vulcanization interparticle crosslinking in film formation and remaining more rigid. The overall results Illustrate clearly that the ultimate mechanical properties of the latex films are strongly dependent on the type of sulfidic bonds formed. This research reveals further the very intricate relationship between the vulcanization methods, sulfur content, and latex type in optimizing the mechanical performance of NR latex products. It provides valuable insights for industry practices aimed at improving the quality and performance of latex-dipped goods.