RDX/AMMO推进剂的分子动力学

Molecular dynamics simulations have been performed to investigate well-known ener-getic material cyclotrimethylene trinitramine (RDX) crystal, 3-azidomethyl-3-methyloxetane (AMMO) and RDX/AMMO propellant. The results show that the binding energies on differ-ent crystalline surface of RDX changes in the order of (010)>(100)>(001). The interactions between RDX and AMMO have been analyzed by means of pair correlation functions. The mechanical properties of RDX/AMMO propellant, i.e. elastic coefficients, modulus, Cauchypressure, and Poisson's ratio, etc., have been obtained. It is found that mechanical properties are effectively improved by adding some amounts of AMMO polymers, and the overall effect of AMMO on three crystalline surfaces of RDX changes in the order of (100)>(010)>(001). The energetic properties of RDX/AMMO propellant have also been calculated and the results show that compared with the pure RDX crystal, the standard theoretical specific impulse of RDX/AMMO propellant decrease, but they are still superior to those of double base propellant.     

Inorganic-Organic Hybrid Polymers Based on Surface-Modified Metal Oxide Clusters

Transition metal oxide clusters with unsaturated carboxylate ligands bonded to their surface were polymerized in the presence of organic co-monomers by various polymerization techniques to form cluster-reinforced polymers. The properties of the cluster-crosslinked hybrid polymers are distinctly different to those of the parent polymers and originate from both crosslinking and filler effects. Variation of the cluster proportion, the kind of employed cluster, the ratio of functional and non-functional capping ligands and the polymerization conditions allows modifying the materials properties of the hybrid materials. The most important changes in materials properties compared with the cluster-free polymers relate to the swelling behavior, thermal stability and mechanical properties. Furthermore, cluster-specific properties can be introduced into the polymers, such as magnetic properties.     

Foamed crosslinked LDPE/PP blends made by hot mold injection molding

Foamed and crosslinked blends of LDPE and i-PP were investigated. The specimens were made by hot mold injection molding process at the temperature of the mold of 210°C. Azodicarbonamide as foaming agent and 2,5-dimethyl-2,5-di(tert.-butylperoxy)hexane as crosslinked agent were used. The chemical changes as a result of the crosslinking were determined by gel content. Thermal behavior of the blends was studied by DSC. The difference of influence of crosslinking agent on chemical changes of both polymers was established. An improvement of the mechanical properties due to crosslinking between PE and PP on their interface was observed. The interaction on the PE/PP interface was confirmed by phase transition parameters determined on the basis of DSC-curves.     

Proton mobility in hydrated sulfonated polystyrene: NMR and impedance studies

Different ionomers were obtained by sulfonation of a commercial polystyrene (PS), using acetyl sulfate as reagent. The sulfonation was assessed by FTIR and XPS spectroscopies and the thermal and mechanical properties were deduced from DMA measurements. The acid form of the ionomers was characterized by means of ¹H and ¹³C MAS-NMR spectroscopies. Polymer hydration under controlled humidity atmosphere was analyzed by gravimetric, NMR and complex impedance techniques. In the hydrated state, two stages associated with formation of hydronium (H₃O⁺) species and proton hopping between adsorbed water molecules were deduced from NMR data. Both processes are responsible for important changes detected in mechanical properties and conductivity of sulfonated polymers during hydration processes.     

Properties and hydrolysis of PLGA and PLLA cross-linked with electron beam radiation

Radiation has been used as a processing tool to modify the properties of polymers. The aim of this study is to understand how electron beam radiation, together with pentaerythritol tetraacrylate (PTTA) as a tetra-functional monomer, can alter the properties (i.e. thermal and mechanical) and hydrolysis rates of PLGA and PLLA. The effects of radiation dose and PFM concentration on the physical properties of the polymers were investigated. The results showed that upon irradiation PLGA and PLLA cross-linked, and an increased in gel content was observed. Glass transition temperature (T_g) and mechanical properties of the polymers also increased. Cross-linked PLGA and PLLA samples were found to retard hydrolytic degradation. The mechanical properties of these polymers were also unaffected by hydrolysis. In summary, PLGA and PLLA cross-linked with PTTA were found to have enhanced mechanical properties and were able to retard hydrolytic degradation.     

Differential reactivity of aromatic diamines during polyimide formation in water

A series of mono and di-imide compounds were synthesized by the reaction of common aromatic diamines with 4,5-dichlorophthalic acid in aqueous solution (at temperature between 160 °C and 200 °C) as a precursor to determining the chemical reactivity changes in these diamines during copolyimide synthesis under the same conditions. The reactivities of the second amino group were shown to reduce dramatically, in number of examples, after substitution had occurred on the first amino group. The effect of these reactivity changes on polymer and copolymer properties was examined by the synthesis of a series of polymers containing two of the diamines with very different reactivity behaviours.The model compounds and polymers were characterized by FTIR, ¹H NMR and where possible by mass spectroscopy. The polymers were also characterized by GPC, Tg and some mechanical properties.     

Macroscopic,microscopic and molecular aspects of fracture in polymers

The distribution of stress at macroscopic and molecular levels can dramatically affect mechanical properties. This paper explores both these aspects. In the first part, quenching operations for polycarbonate and polystyrene were shown to develop favorable residual stresses as well as structural alterations (as manifested by changes in density, hardness, DSC results, etc.). The changes in these glassy polymers can be accompanied by as much as an order of magnitude increase in impact strength and fatigue life. In the other phase of our study, various analytical methods were used to investigate phenomena associated with fracture in oriented semi-crystalline polymers. In the studies reported here, the combined effects of stress and environmental agents on mechanical strength of nylon, polyethylene, and Kevlar fibers were measured. These results, in conjunction with investigations of bond rupture kinetics, suggest that fracture in these materials involve thermally activated chain scission in which the activation energy is aided by stress and the chemical environment. Different mechanisms appear to dominate fracture in spherulitic forms of chemically similar polymers.     

Polyethylene-polystyrene gradient polymers III. Mechanical and rheo-optical studies of relaxation processes

In this paper the structure correlation of PE-PS gradient polymers, modified by styrene LDPE films with their mechanical and rheo-optical properties, is presented. The specific structural changes of both the investigated materials can be demonstrated by using dynamic mechanical deformation studies. The influence of the penetrant on LDPE crystalline and amorphous phase order is shown. Some interesting mechanical behaviour of the gradient polymers, depending on the polystyrene contents, is discussed.     

Polymer nanogels grafted from nanopatterned surfaces studied by AFM force spectroscopy

Nanopatterned cross-linked polymers are important for applications with controlled mechanical properties. Grafted linear and cross-linked polydimethylacrylamide gels on micro- and nanopatterns were created using iniferter-driven quasi-living radical polymerization combined with conventional photolithography and nanosphere lithography. Micropatterned linear polymers reproduce the expected scaling behavior at moderate grafting density. The addition of cross-linker to the polymerization solution leads to an increased tendency of early termination as determined by AFM force spectroscopy. Similarly, nanopatterned linear polymers show reduced thickness in agreement with the expected scaling relationship for nanoisland grafts that have reduced lateral confinement. The addition of cross-linker reintroduces some of the lateral confinement for the length of polymers reported here. The mechanical properties of both the micro- and nanopatterned linear as well as cross-linked polymers were analyzed using an algorithm to objectively determine the contact point in AFM force spectroscopy and two independent Hertz-based analysis approaches. The obtained Young's moduli are close to those expected for homogeneous thick polymer films and are independent of pattern size. Our results demonstrate that polymeric nanopillars with controlled elastic modulus can be fabricated using irreversible cross-linkers. They also highlight some of the factors that must be considered for successful fabrication of grafted nanopillars of defined mechanical and structural properties.     

Structural changes in blends of linear polymers during their physical aging

Structural transformations in the blends of linear polymers polyurethane and polystyrene during multistage physical aging are studied. Effects of the temperature and time of heat treatment and the rate of cooling after heat treatment on the dynamic mechanical properties of the blends are analyzed. Aging at T = 110°C is accompanied by noticeable structural transformations in the polyurethane phase, while chemical changes are absent, as evidenced by thermogravimetric analysis and IR spectroscopy. Additional physical bonds and topological entanglements presumably form between chains in the blends of linear polymers during physical aging.     

Thermal,mechanical and morphological properties of multicomponent blends based on acrylic and styrenic polymers

Multicomponent polymer blends afford polymeric materials with specific properties for many applications. The effect of different chemical structures on the miscibility and compatibility of polymer blends composed of multicomponent acrylic and styrenic polymers was studied in this research. The influence of each component on the thermal, mechanical, and morphological properties, as well as optical transparency, was analyzed in poly (methyl methacrylate), homopolymer (PMMAh), or copolymer (PMMAe) blends where the minority constituents formed by polystyrene (PS), styrene-acrylonitrile copolymer (SAN) or acrylonitrile-butadiene-styrene terpolymer (ABS). The results showed significant changes in the properties of these mixtures due to the effect of the type of chemical structure and different elastomeric domains of the majority and minority components of polymer blends.     

PA66/PA12/clay based nanocomposites: morphology and physical properties

The structure and the physical properties of several polyamide 66 (PA66)/polyamide 12 (PA12) blends containing different amounts of the two polymers and obtained by melt‐blending have been investigated. A low amount of organically‐modified layered silicate (OMLS, 4 wt%) has also been introduced in order to further improve the physical properties and, in particular, to evaluate its effect on the blends' structure and components' miscibility. The microstructure and morphology of all the composites were analyzed by means of X‐Ray diffraction (WAXD), transmission electron microscopy (TEM), and high resolution scanning electron microscopy (SEM), while the macroscopic scale properties (mechanical behavior and water adsorption) were assessed in order to investigate and understand the materials' structure–properties relationships. The partial miscibility of PA66 and PA12, with phase separation depending on blend composition, has been confirmed. The results also underlined the possibility to tailor the behavior of polymer blends in terms of mechanical water adsorption properties by varying the amount of PA12, added to PA66 with and without the addition of the OLMS. The effectiveness of the clay in modifying the components' miscibility as well as its tendency to segregate preferentially within separate PA66 domains have been assessed. WAXD results showed opposite effects of PA12 and clay on the crystallization behavior of PA66, an aspect that has also been deepened in another paper by the same authors discussing the results of the complete thermal characterization. Copyright © 2010 John Wiley & Sons, Ltd.     

Modified Burgers-Reimschuessel model for moisture-sensitive polymers

Viscoelastic properties of moisture-sensitive polymers can be significantly affected by moisture in the ambient environment, resulting in drastic changes in the properties as the absorbed moisture content increases. In this article, a simple yet important modification to the Reimschuessel model is introduced by considering both plasticization and anti-plasticization induced by water molecules. The proposed model is validated against the results of four different polymers obtained by Onogi et al., which demonstrates its capability of describing the available data. This model can be used to estimate the performance and service life of products produced using moisture-sensitive polymers. It also reveals that small amounts of diffused moisture might have a stiffening effect on the mechanical properties of hydrophilic polymers.     

Miscibility-structure-property correlation in blends of ethylene vinyl alcohol copolymer and polyamide 6/66

Blends of ethylene vinyl alcohol (EVOH; 44 mol% ethylene) and polyamide 6/66 (PA; 75 mol% PA 6) random copolymers were studied in the entire composition range. Specific interaction between the components was analyzed by IR spectroscopy; furthermore, coefficients related to the Flory-Huggins interaction parameter were derived from equilibrium water uptake and tensile strength. Morphology of the blends was investigated by thermal analysis (DSC), density measurements, and SEM micrographs. The two polymers form heterogeneous blends in each composition. Although the components crystallize in separate phases, the morphology and the mechanical properties are greatly affected by the association of OH and NH groups. Crystallization is restricted in the blends, and the increase of the amorphous fraction, as well as specific interaction between the components, results in essential improvement in the mechanical properties.     

交联对聚己二酸乙二醇酯聚氨酯/甲基丙烯酸甲酯交联聚合物的力学阻尼、相容性及形态的影响

用紫外光聚合方法制备出一系列端乙烯基聚己二酸乙二醇酯聚氨酯(PEAPU)和甲基丙烯酸甲酯(MMA)AB交联聚合物(ABCP)。用粘弹谱仪、透射电子显微镜(TEM)和平衡溶胀法研究了AB交联聚合物的动态力学性能、玻璃化转变温度、形态和交联密度、观察到相应于聚氨酯和PMMA相两个玻璃化转变温度,TEM照片中的微相分离是更明显的,ABCP中的两个T_g内移表明,两种成分的化学交联增加了相互的可混性、与ABCP具有相同组成的IPN有比ABCP大得多的相区。氢键能够影响ABCP的相容性、形态和动态力学性能。     

The characterization of polymer deformation by rheo-optical fourier-transform infrared spectroscopy

The mechanical properties of polymeric materials are of considerable importance to their engineering applications. Apart from the chemical structure and the thermal history, molecular orientation has a major influence on the mechanical properties of a polymer. The increased need for more detailed data and a better understanding of the mechanisms involved in polymer deformation has led to the search for new experimental techniques to characterize transient structural changes during mechanical processes. With the advent of rapid-scanning Fourier - transform infrared (FTIR) spectroscopy, simultaneous vibrational spectroscopic and mechanical (so-called rheo-optical) measurements during the deformation of polymers have emerged as a very informative probe for the study of deformation and relaxation phenomena in polymer films in the late seventies and have since then been applied to obtain data on strain-induced crystallization and orientational and conformational changes during mechanical treatment of a wide variety of polymers.     

Insulating Polymers as Additives to Bulk-Heterojunction Organic Solar Cells: The Effect of Miscibility

Adding insulating polymers to conjugated polymers is an efficient strategy to tailor their mechanical properties for flexible organic electronics. In this work, we selected two insulating polymers as additives for high-performance photoactive layers and investigated the mechanical and photovoltaic properties in organic solar cells (OSCs). The insulating polymers were found to reduce the electron mobilities in the photoactive layers, and hence the power conversion efficiencies were significantly decreased. More importantly, we found that the insulating polymers exhibited negative effect on the mechanical properties of the photoactive layers, with reduced Young's modulus and low crack onset strains. Further studies revealed that the insulating polymers had poor miscibility with the photoactive layers, providing large domains and more cavities in blend thin films, which act as negative effect for the tensile test. The studies indicate that rational selection of insulating polymers, especially enhancing the non-covalent interaction with the photoactive layers, will be critically important for the stretchable OSCs.     

Molecular dynamics simulations of trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin-based polymer-bonded explosives

Molecular dynamics has been applied to investigate the low-sensitivity explosive TNAD (trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin)-based polymer-bonded explosives (PBXs) with four typical fluorine polymers, PVDF (polyvinylidenedifluoride), PCTFE (polychlorotrifluoroethylene), F(2311) (fluorine rubber), and F(2314) (fluorine resin). The elastic constants, mechanical properties (tensile modulus, bulk modulus, shear modulus, and Poission ratio), binding energies, and detonation performances are first reported for the TNAD-based PBXs. The results show that the mechanical properties of TNAD can be effectively improved by the addition of small amounts of fluorine polymers, and the overall effect of fluorine polymers on the mechanical properties of the PBXs along three crystalline surfaces is (001) > (010) > (100). On each crystal surface, improvement in the ductibility made by the fluorine polymers changes approximately in the sequence of PVDF > F(2311) > F(2314) > PCTFE. The binding energies between different TNAD crystalline surfaces and different polymer binders with the same chain segment or mass fraction both decrease in the order of (010) > (100) > (001). The binding properties of the polymers with the same chain segment on each crystal surface of TNAD increase as PVDF < F(2311) < F(2314) < PCTFE, while those of different polymers in the same content decrease in the sequence of PVDF > F(2311) > F(2314) > PCTFE. The detonation performances of the PBXs decrease in comparison with the pure crystal, but they are superior to those of TNT.     

Structure-property relationships for novel wholly aromatic polyamide-hydrazides containing various proportions of para-phenylene and meta-phenylene units: I. Synthesis and characterization

A series of novel wholly aromatic polyamide-hydrazides was synthesized by a low temperature solution polycondensation reaction of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either terephthaloyl chloride (TCl), isophthaloyl chloride (ICl), or mixtures of various molar ratios of TCl and ICl in anhydrous N,N-dimethylacetamide (DMAc) as a solvent. Polymer structures were identified by elemental analysis and infrared spectroscopy. All the polymers have the same structural formula except the way of linking phenylene units inside the polymer chain. The content of para- and meta-phenylene moieties was varied within this series so that the changes in the latter were 10 mol % from polymer to polymer, starting from an overall content of 0-100 mol %. The prepared polymers were characterized for their properties in order to acquire clear understanding of the influence exerted by controlled structural variations in these polymers upon some of important properties, such as solubility, intrinsic viscosity, moisture regain, mechanical properties and thermal as well as thermo-oxidative stability. The polymers were readily soluble in several organic polar solvents such as DMAc, N,N-dimethylformamide, dimethyl sulphoxide, N-methyl-2-pyrrolidone and hexamethyl phosphoramide and could be cast into flexible films. Their solubilities were found to increase remarkably with introduction of meta-phenylene moieties into the polymer chains. Their intrinsic viscosities ranged from 0.73 to 4.83 dl g⁻¹ in DMAc at 30 °C and increased with the increase of para-phenylene units content. Mechanical properties of the films produced from these polymers are improved markedly by substitution of para-phenylene units for meta-phenylene units. Thermogravimetric studies revealed that the completely para-oriented type of polymer has better thermal and thermo-oxidative stability relative to that of the other polymers. Moreover, the results reveal that the prepared polymers have a great affinity to water sorption. The hydrophilic character increases as a function of meta-oriented phenylene rings incorporated into the polymer chains.     

STUDY ON CASTOR OIL POLYURETHANE/POLY (METHYL METHACRYLATE) AB CROSSLINKED POLYMERS

Castor oil polyurethane/poly(methyl methacrylate) AB crosslinked polymers (ABCP) were synthesized by free radical copolymerization of MMA and vinyl-terminated castor oil polyurethane which was obtained from isocyanate-terminated castor oil polyurethane and hydroxyethyl methacrylate The mechanical properties, transition and relaxation, as well as compatibility and morphology of the ABCP were investigated by changing the component. The results show that the ABCP is a semicompatible system and the compatibility of the two components decreases with increasing content of the hard segment. The mechanical and damping properties of the ABCP are obviously superior to that of their homopolymers. The damping value is mainly controlled by cross[ink density of the ABCP but the T-g value by component.