In order to reveal the relationship between 3,3-bis (azidomethyl) oxetane-tetrahydrofuran copolyether (P (BAMO-THF)) microstructure and its macro properties, the segment sequence structure of a kind of P(BAMO-THF) was characterized using quantitative 13 C-NMR analysis. It was found that the P(BAMO-THF) is composed of equimolar comonomers whose randomness factor (R) is 1.09, belonging to a quasi-ideal random copolymer. Combining DSC and polarizing optical microscopy, it was verified that the thermal-effect between 28 8C and 41 8C attributes to the melt-ing of the P(BAMO-THF)spherulites. Using WAXRD, it was suggested that the aggregation of BAMO micro-blocks among P(BAMO-THF) polymeric chains causes the formation of spherulites. The viscosity measurement clearly demonstrated that, below 30 8C or above 40 8C, the P (BAMO-THF) viscosities change slowly as a function of temperature. Conversely, between 30 8C and 40 8C, its viscosities sharply decline with the increase in temperature because of the changes in its morphology.
Ethylene oxide−tetrahydrofuran copolyether (P(E-co-T)) crosslinked with isocyanate Desmodur (N100) is widely used as the binder system in solid energetic propellant. The effect of its cross-linking degree on the physical properties is important for the evaluation of the propellant binders. In this work, an efficient method was presented for simulating the crosslinking process, predicting the microscopic behaviors and macroperformances of cross-linked P(E-co-T)−N100 binder systems. During the simulation of cross-linking network forming, the initial physical mixture model of P(E-co-T)/N100 was firstly constructed and optimized through molecular dynamics. Then the possible cross-linking topology was generated by means of the identification of the reactive site pairs. In this way, the P(E-co-T)−N100 cross-linking pathway was realized by alternate structure optimization and junction reaction. The cross-linking intermediate models were analyzed, and the density and mechanical property profiles have revealed the increasing tendency with cross-linking progressing, which is corresponding to the experimental results. Moreover, volume−temperature behaviors of P(E-co-T) and cross-linked P(E-co-T)−N100 systems were simulated to study the cold resistance characterized by glass transition temperature. The mean-squared displacements and free volume data have verified that the cross-linking structure of P(E-co-T)−N100 restricts the molecular mobility, which is helpful to explain the higher glass transition temperature and stronger mechanical properties.
Thermoset polyurethane elastomers made from poly(3,3-bis(azidomethyl) oxetane with tetrahydrofuran) and various multifunctional isocyanate cross-linkers were compared to uncover a new mechanism of modulating the mechanical properties. Extra hydrogen bonding motifs, such as urethane or urea, were built in the cross-linkers and were proved to essentially determine the stiffness and toughness of the elastomers, while the covalent cross-linking densities of both networks were controlled strictly at the same level. The impact of interchain H-bonding on the mechanical properties of the polyurethane thermoset was unprecedently emphasized and supported by evidence from Fourier-transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), and low-field nuclear magnetic resonance (LFNMR).
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