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The crystallization behavior of polyamide 6,6 (PA66) under complex flow field is of great importance for its final mechanical properties. Poly(vinyl pyrrolidone) (PVP) was applied as crystallization modifying agency to improve processability of PA66. The regulation nature on hydrogen bonds (H-bonds) interaction of PVP was studied upon cooling process. As revealed by in situ FTIR, the sample with 5 wt% PVP displays decreased enthalpy change (ΔH) for both the generation of H-bonds and the transition of H-bonds from "disordered" to "ordered" state, which illustrates the molecular mechanism for the regulation of crystallzation behavior. Moveover, 2D-WAXD is applied to reveal the evolution of microstructure for sample under external injection field. Hermans orientation factor (fH) decreases obviously with the addition of PVP, because the relaxation of chain segments is promoted as well the crystallization is retarded. The above crystallization and microstructure changes during the processing provokes the improvement of processability without the apparent sacrifice of mechanical properties. [ABSTRACT FROM AUTHOR]

Well-defined polypropylene grafted silica nanoparticles (PP-g-SiO2) were prepared through the reaction of maleic anhydride grafted polypropylene (PP-g-MAH) with amino-functionalized silica (SiO2-NH2) by the 'grafting-to' method. The grafting density of PP-g-SiO2 is found to be controlled by the concentration of silane coupling agent 3-[2-(2-aminoethylamino) ethyl amino] propyl trimethoxy silane (TAMS). The maximum grafting density of grafted PP-g-MAH chains with molecular weight of 9100 g/mol could reach 0.34 chains/nm2, when the critical concentration of TAMS was 0.0194 mol/L. The critical concentration of TAMS can be explained by the maximum amounts of primary amino groups, which can totally react with PP-g-MAH on the surface of SiO2-NH2, when the silane monolayer is formed. The synthesized PP-g-SiO2 with different molecular weights was mixed with PP by solution mixing to form a series of nanocomposites. The crystallization temperature (Tc) of nanocomposites increased significantly with the particle loading. The PP-g-SiO2 with high molecular weight of grafted chains exhibits a high nucleation ability at 1 wt% nanoparticle loading in PP/PP-g-SiO2 nanocomposites. In summary, we provide an effective method to synthesize the well-defined PP-g-SiO2 with controlled grafting density, which shows excellent nucleation ability. [ABSTRACT FROM AUTHOR]

The Chinese Journal of Polymer Science has published a special issue on Functional Polymer Materials, highlighting the significant role of polymer materials in various fields such as industry, medicine, energy, and the environment. The issue features research papers from 12 young scholars covering topics such as thermal conduction, flame retardancy, electromagnetic wave absorption, water harvesting, holographic imaging, and electromagnetic interference shielding. The papers provide scientific analyses and innovative ideas, offering valuable knowledge and inspiration. The journal aims to stimulate further research interest in functional polymer materials and advance the field of polymer science. [Extracted from the article]

The crystallization kinetics of semicrystalline polymers is often studied with isothermal experiments and analyzed by fitting the data with analytical expressions of the Avrami and Lauritzen and Hoffman (LH) theories. To correctly carry out the analysis, precautions in both experiments and data fitting should be taken. Here, we systematically discussed the factors that influence the validity of the crystallization kinetics study. The basic concepts and fundamentals of the Avrami and LH theories were introduced at first. Then, experimental protocols were discussed in detail. To clarify the impact of various experimental parameters, selected common polymers, i.e., polypropylene and polylactide, were studied using various experimental techniques (i.e., differential scanning calorimetry and polarized light optical microscopy). Common mistakes were simulated under conditions when non-ideal experimental parameters were applied. Furthermore, from a practical point of view, we show how to fit the experimental data to the Avrami and the LH theories, using an Origin® App developed by us. [ABSTRACT FROM AUTHOR]

The existence of tumor immunosuppressive microenvironment (TIME) is the major determinant for the poor efficacy of current tumor immunotherapy. Tumor-associated macrophages (TAMs) tend to become tumor-promoting M2-like phenotype and hinder immune response in solid tumors. Repolarization of TAMs from M2 to anti-tumor M1 phenotype is robust for remodeling the TIME. Herein, we developed a redox-responsive nanogel as the delivery system of Toll-like receptor 7 and 8 (TLR7/8) agonist (R848) prodrug for potent cancer immunotherapy. The nanogel (denoted as R848-Gel) was obtained by emulsion polymerization of HSEMA and R848 prodrug (R848-HSEMA), whose size was appropriate 100 nm. R848-Gel could be internalized by macrophages and dendritic cells in vitro, and effectively repolarized M2 into M1 macrophages and promoted the maturation of antigen-presenting cells. In vivo study indicated that the R848-Gel showed a stronger tumor inhibitory effect and no drastic body weight change compared with free drug. Immune cell analysis after the treatment indicated that R848-Gel was helpful to activating the TIME. In summary, this study provides a simple but effective vehicle for R848 to improve cancer immunotherapy. [ABSTRACT FROM AUTHOR]

The polymorphic transition of trans-1,4-polyisoprene (TPI) during stretching was investigated by in situ wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The influences of the initial structure, stretching temperature, and strain rate on the contents of different crystal modifications (α, β) were explored. The results confirm that the α-β transition occurs during stretching of TPI that only contains α crystal (α-TPI). When the stress is relaxed, the β crystal formed during stretching remains, which indicates that the transition is irreversible. On the other hand, stretching of TPI that only contains β crystal (β-TPI) results in orientated β crystal. No β-α transition occurs during stretching. The different structures of stretched α-TPI and β-TPI exclude the previously proposed "melting-recrystallization mechanism". The α-β transition depends significantly on temperature and strain rate, indicating the transition is governed both by thermodynamics and kinetics. Our results support a solid-solid transition mechanism rather than a melting-recrystallization mechanism. The irreversible nature of the transition is attributed to the metastability of the β phase in the unstretched state. Different from the "β phases" that appear in polymers with stress-induced reversible transitions, e.g. poly(butylene terephthalate) and poly(butylene succinate), the stability of β phase in TPI is high that can be long-lived. The strain rate dependence of α-β transition hinders the determination of critical stress for the transition. It further indicates that the local stress within the sample is more heterogeneous at higher strain rates. [ABSTRACT FROM AUTHOR]

Stimulus-responsive polymers containing dynamic bonds enable fascinating properties of self-healing, recycling and reprocessing due to enhanced relaxation of polymer chain/network with labile linkages. Here, we study the structure and properties of a new type of thermoplastic polyurethanes (TPUs) with trapped dynamic covalent bonds in the hard-phase domain and report the frustrated relaxation of TPUs containing weak dynamic bond and π-π interaction in hard segments. As detected by rheometry, the aromatic TPUs with alkyl disulfide in the hard segments possess the maximum network relaxation time in contrast to those without dynamic bonds and alicyclic TPUs. In situ FTIR and small-angle scattering results reveal that the alkyl disulfide facilitates stronger intermolecular interaction and more stable micro-phase morphology in π-π interaction based aromatic TPUs. Molecular dynamics simulation for pure hard segments of model molecules verify that the presence of disulfide bonds leads to stronger π-π stacking of aromatic rings due to both enhanced assembling thermodynamics and kinetics. The enhanced π-π packing and micro-phase structure in TPUs further kinetically immobilize the dynamic bond. This kinetically interlocking between the weak dynamic bonds and strong molecular interaction in hard segments leads to much slower network relaxation of TPU. This work provides a new insight in tuning the network relaxation and heat resistance as well as molecular self-assembly in stimulus-responsive dynamic polymers by both molecular design and micro-phase control toward the functional applications of advanced materials. [ABSTRACT FROM AUTHOR]

The Theological property evolution of polyamide 1012 (PA1012) in the isothermal process in molten state has been investigated. The results show that the viscosity increases and crosslinking reaction occurs simultaneously together with the increase of temperature, thus causing the variation of storage modulus (G′) and loss modulus (G″) in the repeated frequency sweeps with residual time. This research has pointed out that the superposition is valid for monitoring the complex behavior composed of the viscosity increasing and crosslink occurring process by tracing the variation behavior of the crossover points of G' and G" with time, revealing the same time-temperature dependence of the two reactions in the isothermal process. A normalized master curve has been proposed to describe the melt behavior at a given temperature. [ABSTRACT FROM AUTHOR]

Crosslinking reactions of high density polyethylene with low peroxide concentrations ranging from 0.1 wt% to 1.0 wt% at temperatures of 170, 180 and 190 °C were monitored by rheological measurements. A critical gel forms at the peroxide concentration of 0.2 wt%, where the transition from long chain branching generation to crosslinking network formation could occur. Rheokinetics of crosslinking can be fitted well by Ding-Leonov's model. The curing rate k at the earlier stage exhibits about 3 times acceleration per 10 °C with increasing temperature, while the equilibrium modulus G′ at the fully cured stage is almost independent of temperature. Influences of crosslinking on the subsequent crystallization behaviors were detected by DSC measurements. Above the critical gel concentration, crystallization is largely retarded as evidenced by the lower crystallization temperature T and crystallinity X due to the network formation. The secondary crystallization valley located at the temperature near 80 °C can be observed above the critical concentration, which becomes more evident with the increasing peroxide concentration and curing temperature. This phenomenon provides another evidence of crystallization retardation by the crosslinking network. [ABSTRACT FROM AUTHOR]

PA1012/calcium silicate whisker nanocomposites with contents of whisker ranging from 10 wt% to 40 wt%, are prepared by twin screw extruder without any additions of coupling agent. The effect of whisker on the matrix is analyzed by the studies of morphology, the mechanical properties, water absorption and thermal stabilities. SEM micrographs obviously demonstrate, even under the high filler content of 40 wt% and without surface treatment, calcium silicate whisker can be homogeneously dispersed in polyamide, directly leading to the enhanced mechanical properties. The mechanism of higher efficiency of reinforcement is needle-like shape whisker, having access to be intercalated, and mutual affinity caused by hydrogen bonding interaction between carbonyl group in polyamide chain and hydroxyl group in whisker surface. Both aspects attach matrix with excellent stress-transfer properties. In addition, with the assistance of whisker, the nanocomposite favors an improved water absorption as well as thermal stability, which is intimately associated with physical performance. [ABSTRACT FROM AUTHOR]

Polyester-based biodegradable polyurethane (PU) with different hard segment ratios was selected to modify the impact toughness of poly(L-lactide) (PLLA). The influence of blending composition and hard segment ratio of PU on the phase morphology, crystallization behavior and mechanical properties of PLLA/PU blends has been investigated systematically. The results showed that the PU particles were uniformly dispersed in PLLA matrix at a scale from submicrons to several microns. The glass transition temperature of PU within these blends decreased compared to that of neat PU, but rose slightly with its content and hard segment ratio. The presence of PU retarded the crystallization ability of PLLA, whereas enhanced its elongation at break and impact resistance effectively. As the PU content reaches up to 30 wt%, the phenomenon of brittle-ductile transition occurred, resulting in a rougher fracture surface with the formation of fibril-like structure. Moreover, under the same concentrations, the elongation at break and impact strength of PLLA blends decreased slightly with the increase of hard segment ratio of PU. [ABSTRACT FROM AUTHOR]

The morphology evolution and the corresponding linear viscoelastic behavior of the phase-separating polybutadiene (PB)/low vinyl content polyisoprene (LPI) blend have been investigated by phase contrast optical microscopy (PCOM), small-angle light scattering (SALS) and rheometry. Two kinds of structure evolutions and rheological responses have been observed. It is found that the co-continuous structure generally gives a power law behavior of the dynamic storage modulus versus frequency and the coarsening of co-continuous structure leads to a decrease of the storage modulus. For the droplet-matrix structure, a platform modulus is observed at the mediate frequencies, followed by the typical terminal relaxation behavior of storage modulus at the extremely low frequencies. The decreasing platform modulus and increasing terminal modulus with the growth of droplets are observed and can be well interpreted by the simplified Palierne model. The platform modulus and terminal modulus at a given frequency are found to be scalable with the phase separation time. Besides, the characteristic relaxation time and domain size of the droplets have been obtained by rheology. And it seems that the rheologically determined droplet dimensions are consistent with the ones determined by PCOM and SALS. [ABSTRACT FROM AUTHOR]

In the present work, the blend of poly(butylene succinate) (PBS) and bisphenol A (BPA) was prepared by solution mixing, and the intermolecular interactions between the two components were characterized by a combination of nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The results showed that intermolecular hydrogen-bonding forms between the carbonyl group of PBS and phenol hydroxyl of BPA. With the increase of BPA content, more hydrogen bonds were formed. The effect of hydrogen bonding on the crystallization behavior of PBS was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results showed that the overall isothermal crystallization kinetics and the spherulite growth rate of PBS decrease with the increase of BPA content, while the PBS spherulite size increases with BPA content. [ABSTRACT FROM AUTHOR]

In the present work, structure changes during stretching of isotactic polypropylene ( iPP) and iPP/silicon dioxide (SiO) composites have been investigated systematically. The α-form crystal structure of both iPP and iPP/SiO composites is destroyed and transforms into the mesophase as the samples are stretched at a low temperature (35°C), while stretching at high temperatures (90°C and 120°C) can restrain the appearance of defects and keep the perfection of crystal structure. FTIR results reveal that the stretching temperatures show no obvious difference of the effect on the orientation of pure iPP, however, the orientation of iPP/SiO composites is greatly changed by the tensile temperature. In the case of micron-sized SiO particles (average particle diameter d > 1 μm), the orientation of the composites is lower than that of pure iPP at all stretching temperatures. The above results suggest that the stretching temperature and the SiO particle size have great influence on the structure variation and orientation behavior of iPP/SiO composites. [ABSTRACT FROM AUTHOR]

The master curves of a series of aliphatic polycarbonates (APCs) with different lengths of methylene segments in the repeat unit were obtained by dynamic rheological measurements. The plateau modulus and entanglement molecular weight were determined and cross-checked by different methods. Though having distinct difference in chemical structure of repeat units, both APCs and bisphenol-A polycarbonates have the similar entanglement weight and entanglement spacing. On the other side, the plateau modulus decreases with increasing the length of the side group of aliphatic polycarbonates with different side-chain lengths in the literature. The packing length model can explain the relationship between chain structure and entanglements. [ABSTRACT FROM AUTHOR]

The early stage of polymer crystallization may be viewed as physical gelation process, i.e., the phase transition of polymer from liquid to solid. Determination of the gel point is of significance in polymer processing. In this work, the gelation behavior of poly(butylene succinate) (PBS) at different temperatures has been investigated by rheological method. It was found that during the isothermal crystallization process of PBS, both the storage modulus ( G′) and the loss modulus ( G″) increase with time, and the rheological response of the system varies from viscous-dominated ( G′ < G″) to elastic-dominated ( G′ > G″), meaning the phase transition from liquid to solid. The physical gel point was determined by the intersection point of loss tangent curves measured under different frequencies. The gel time ( t) for PBS was found to increase with increasing crystallization temperature. The relative crystallinity of PBS at the gel point is very low (2.5%-8.5%) and increases with increasing the crystallization temperature. The low crystallinity of PBS at the gel point suggests that only a few junctions are necessary to form a spanning network, indicating that the network is 'loosely' connected, in another word, the critical gel is soft. Due to the elevated crystallinity at gel point under higher crystallization temperature, the gel strength S increases, while the relaxation exponent n decreases with increasing the crystallization temperature. These experimental results suggest that rheological method is an effective tool for verifying the gel point of biodegradable semi-crystalline polymers. [ABSTRACT FROM AUTHOR]

Syndiotactic polypropylene ( sPP) as-spun fiber ( sPP1) and drawn fiber ( sPP2) were prepared by melt-spinning and melt-spinning/hot-drawing, respectively. The structure transition of the two fibers induced by annealing at different temperatures and the corresponding mechanical properties were subsequently investigated by the combination of Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD) and tensile testing. The results indicate that the chain conformation and crystal forms of the two sPP fibers are not obviously changed at low annealing temperature (40°C). With increasing the annealing temperature, the trans-planar conformation and mesophase in sPP1 and sPP2 fibers can be completely transformed to helical conformation and crystal form I under tension. Upon removing the tension, a small amount of mesophase and trans-planar conformation will be regained. The mechanical properties of the annealed fibers are manifestly dependent on their initial structure and the annealing temperature. [ABSTRACT FROM AUTHOR]