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The acetylene‐terminated polyisoimide oligomers introducing 2,2′‐bis (trifluoromethyl)benzidine (TFMB) or 3,4′‐oxydiphthalic anhydride (3,4′‐ODA) as the diamine were synthesized, and short quartz fiber reinforced polyisoimide composites were prepared. The structure, processability, and thermal properties of polyisoimide oligomers were characterized. The mechanical properties and ablation protection performances of the composites were tested. The effects of TFMB on the processability and thermal properties of polyisoimides were studied. The application properties of short quartz fiber reinforced polyisoimide composites as thermal protection materials were evaluated by coal gas/oxygen ablation test system. These results showed that the introduction of TFMB into the polyisoimide structure can improve its solubility and heat resistance, as well as the ablation protection performances of the composites. The above results showed its potential application in the field of thermal protection materials. This makes it possible for polyisoimide composites to be used in the field of ablation protection. [ABSTRACT FROM AUTHOR]

The application of phase delay property of complementary split-ring resonator (CSRR)-loaded transmission line in the miniaturisation of Butler matrix beam forming network is proposed. The design of left-handed transmission line and the influence of the capacitive stubs in the phase delay properties of the CSRR-loaded transmission line with a gap are presented. The CSRR-loaded transmission line with a 7 mm capacitive stub provides 93' more phase delay than the CSRR-loaded transmission line without the stubs. CSRR-loaded transmission line with capacitive stubs is applied to the phase compensating lines of 4×4 Butler matrix configurations, without disturbing the 90' hybrids and crossovers. The CSRR-loaded configuration exhibits a size reduction of 48% of the footprint of the conventional Butler matrix. The output of the miniaturised Butler matrix is connected to a linear microstrip antenna array of four radiating elements and its radiation parameters (beam pointing direction, beamwidth and sidelobe levels) are compared with that of an unloaded conventional 4×4 Butler matrix. The miniaturised switched beam-steering antenna exhibits similar radiation characteristics as that of a conventional switched beam antenna. [ABSTRACT FROM AUTHOR]

We develop novel parallel algorithms that allow molecular dynamics simulations in which byproduct molecules are created and removed because of the chemical reactions during the molecular dynamics simulation. To prevent large increases in the potential energy, we introduce the byproduct molecules smoothly by changing the non‐bonded interactions gradually. To simulate complete equilibrium reactions, we allow the byproduct molecules attack and destroy created bonds. Modeling of such reactions are, for instance, important to study the pore formation due to the presence of e.g. water molecules or development of polymer morphology during the process of splitting off byproduct molecules. Another concept that could be studied is the degradation of polymeric materials, a very important topic in a recycling of polymer waste. We illustrate the method by simulating the polymerization of polyethylene terephthalate (PET) at the coarse‐grained level as an example of a polycondensation reaction with water as a byproduct. The algorithms are implemented in a publicly available software package and are easily accessible using a domain‐specific language that describes chemical reactions in an input configuration file. © 2018 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

ABSTRACT: The dynamic and mechanical properties of the three thermoplastic polyimides—crystallizable polyimide BPDA‐P3 and amorphous polyimides ODPA‐P3 and aBPDA‐P3—have been simulated using the atomistic molecular dynamics technique. The three simulated polyimides differ in the chemical structure of their corresponding dianhydride fragments. Analyzing the local orientational mobility of different phenylene rings, it has been established that the increase of the glass‐transition temperature (Tg) in the ordered set T g aBPDA − P 3 > T g BPDA − P 3 > T g ODPA − P 3 is caused by the slowing down of the phthalimide rings relaxation in the corresponding dianhydride fragments. It has been observed that rather poor mechanical characteristics upon aBPDA‐P3 stretching in the strain‐hardening regime are also due to the low orientational mobility of the phthalimide rings. The correlation between the dynamic fragility and the polyimides strain‐hardening moduli has been observed; the increase of the dynamic fragility leads to the increase of the strain‐hardening modulus. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 375–382 [ABSTRACT FROM AUTHOR]

ABSTRACT Two new bio-based diacylhydrazide monomers, namely, 4,4′-(propane-1,3-diylbis(oxy))bis(3-methoxybenzohydrazide) and 4,4′-(propane-1,3-diylbis(oxy))bis(3,5-dimethoxybenzohydrazide) were synthesized starting from lignin-derived phenolic acids, namely, vanillic acid and syringic acid. A series of poly(amide imide)s was synthesized by polycondensation of these diacylhydrazide monomers with commercially available aromatic dianhydrides. Poly(amide imide)s showed inherent viscosity in the range 0.44-0.56 dL g−1 and exhibited good solubility in organic solvents. Poly(amide imide)s could be cast into transparent, flexible, and tough films from their N, N-dimethylacetamide solutions. Poly(amide imide)s showed 10% weight loss in the temperature range 340-364 °C indicating their good thermal stability. Glass transition temperature ( Tg) of poly(amide imides)s were measured by DSC and DMA which were in the range 201-223 °C and 214-248 °C, respectively. The Tg values of poly(amide imide)s were dependent on the number methoxy substituents on aromatic rings of diacylhydrazide monomers. Molecular dynamics simulation studies revealed that chain rigidity is the dominant factor for observed trends in Tg. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3636-3645 [ABSTRACT FROM AUTHOR]

A phenylethynyl-terminated reactive diluent [Card-4-phenylethynylphthalic anhydride (PEPA)], which contained fluorenyl cardo structures, was successfully synthesized and used as a modifier for flexible phenylethynyl-terminated imide oligomer (PEI-PEPA). The chemical structure, crosslink characterization, molecular weights, and thermal properties of the products were characterized. The imide systems with addition of 10, 20, 30, and 40 wt% Card-PEPA to PEI-PEPA (PEI-PEPA-Card) and their cured resin systems were prepared. The thermal curing behaviors of imide systems at different heating rates were analyzed by using differential scanning calorimetry. Thermal properties such as glass transition temperature ( Tg) and char yield at 800°C of the resultant resin systems were studied by differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The rheological properties were also investigated using a dynamic rheometry. These properties were found to be outstanding compared with pure PEI-PEPA. The uncured imide systems exhibited lower Tg and lower isothermal viscosity with addition of Card-PEPA. Furthermore, the Tg and char yield of the cured resin systems increased with addition of Card-PEPA. The cured resin systems containing 40 wt% Card-PEPA exhibited the highest Tg of 359°C and char yield at 800°C of 66.5%. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Using systematic coarse-grained (CG) techniques such as iterative Boltzmann inversion (IBI) is an efficient means to simulate high molecular weight polymer melts within reasonable computational time. One drawback of such an approach is however the need to carry out extensive atomistic simulations in order to extrapolate the necessary distributions to derive the inter and intrabead force field parameters. Here it is shown that it is possible to use atomistic simulations of relative short oligomers to develop the CG model for high molecular weight polymers. In particular for the specific case of polycarbonates, it is found that the structural properties (end-to-end distance, radius of gyration and their distributions) are similar irrespective of whether the CG potentials are derived from 5-mer or 10-mer melt systems. Dynamical properties of the CG systems are smoother and faster than the atomistic ones. Scaling factor, derived by overlapping the CG mean square displacement curves (obtained from different CG IBI potentials) over the atomistic ones, also scales the autocorrelation functions. A prediction of the dynamical scaling factor in the case of the unavailability of atomistic simulations is also discussed. The dynamical properties of the CG melts are modeled reasonably well by all the CG potentials derived from atomistic simulations of short oligomers. [ABSTRACT FROM AUTHOR]

An important high-temperature polyimide, namely HFPE-30, has been coarse grained to three different levels of detail. It has been shown that while it is possible to successfully calibrate bonded and non-bonded forcefields and attain realistic densities with all levels of coarse graining, reproducing chain structures and dynamic properties requires an adequate level of atomistic detail to be retained. A model that coarse grains the HFPE-30 molecule into eight beads, approximates both chain structure and dynamic properties well. Alternately, the unrealistically fast dynamics in coarse-grained models can be slowed down by increasing the thermal coupling constant by a scaling factor that is estimated by comparing mean square displacements in detailed atomistic and coarse-grained simulations. In general, stress-strain responses of coarse-grained systems do not match those of the detailed atomic systems except when the coarse graining involves eight beads. In cases where lesser number of beads are used, slowing the dynamics down by the estimated scaling factor takes the stress-strain response of the coarse-grained system close to that of the detailed atomistic one. [ABSTRACT FROM AUTHOR]

ZnAl2O4–TiO2 (ZAT)/polytetrafluoroethylene (PTFE) composites were prepared by powder processing method. The structure and microstructure of the composites were analyzed using X-ray diffraction and scanning electron microscopic techniques. The effect of different volume fraction of ZAT (0–0.6) on the dielectric properties of the composites was investigated at 1 MHz and at the microwave frequency of 7 GHz. The dielectric properties (relative permittivity and dielectric loss) were found to increase with the ZAT content. The samples with 60 vol.% of ZAT filler showed a relative permittivity of 3.9 and dielectric loss of 0.009, respectively, at 7 GHz. The variation of relative permittivity and dielectric loss showed only a very small variation with temperature in the range 25°–70°C for various ZAT/PTFE composites. The relative permittivity obtained experimentally were compared with that of the theoretical values predicted using modified Lichtenecker, Jayasundere—Smith, and Series mixing formulae. They were found to agree well with the predicted values for low filler content. [ABSTRACT FROM AUTHOR]