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Vinyl‐substituted hydridopolycarbosilane (VHPCS) is widely studied for its low viscosity, abundance of active functional groups, rapid curing, and high ceramic yield. The curing reactions mainly involve the free radical polymerization of vinyl and hydrosilylation reactions, but these reactions typically require high temperatures such as 160–250°C. The curing behavior of VHPCS‐17 with a tert‐butyl peroxybenzoate/Nickel acetylacetonate (TBPB/NIAA) system is investigated using differential scanning calorimetry and in situ Fourier transform infrared. The properties of VHPCS‐17 with different initiator systems and VHPCS with different vinyl contents (under TBPB/NIAA system) are studied using thermogravimetric analysis and x‐ray diffraction. The results demonstrate that the TBPB/NIAA system can facilitate the free radical polymerization of vinyl; moreover, this system decreases the peak temperature of the curing reaction from 251 to 141°C and increases the ceramic yield from 80.49% to 89.88%. The ceramic yield of cured VHPCS increases gradually, reaching 89.88% when the vinyl content is 17%. The grain size of β‐SiC decreases continuously with the increase in vinyl content, while the high‐temperature oxidation‐resistant properties of SiC ceramics obtained from different VHPCSs are not negatively affected. [ABSTRACT FROM AUTHOR]

Liquid hydridopolycarbosilanes (LHPCS) with vinyl or allyl groups have attracted significant research interest due to their low curing temperature and high ceramic yield. In this study, allyl-terminated hydridopolycarbosilane (AHPCS) and vinyl-terminated hydridopolycarbosilane (VHPCS) were prepared by the Grignard coupling reaction and characterized by NMR and Fourier infrared spectroscopy (FTIR). And the curing reactions of AHPCS and VHPCS with or without initiators (dicumyl peroxide [DCP], tert-Butyl peroxybenzoate [TBPB]) or Karstedt catalyst were investigated using differential scanning calorimetry and in-situ FTIR. The main curing reactions of VHPCS and AHPCS are the double bond free radical polymerization and hydrosilylation reaction, respectively. The addition of initiators and Karstedt catalyst could promote the corresponding curing reaction and increase the weight residual at 1000°C. The thermal properties of the cured resins were investigated by thermogravimetric analysis. The addition of initiators and catalyst could significantly increase the weight residual of VHPCS and AHPCS, respectively. The addition of the Karstedt catalyst increased the weight residual of AHPCS from 75.6% to 83.1%. In addition, the addition of TBPB and DCP increased the weight residual of VHPCS from 74.2% to 81.2% and 80.2%, respectively. [ABSTRACT FROM AUTHOR]

In order to study the curing process of hydroxyl‐terminated polyether (HTPE) with different curing agents, aliphatic triisocyanate (N100) and toluene diisocyanate (TDI), the crosslink density (XLD) and chemical processes of the curing reactions have been investigated by low‐field NMR spectroscopy and FTIR spectroscopy, respectively, while the mechanical properties of those two cure systems were studied as well. The results show that, for either HTPE/N100 or HTPE/TDI, the higher curing temperature leads to the shorter curing time to reach stability of XLD, while the final XLD decreases by increasing the temperature. The XLD and tensile strength of HTPE/TDI are both lower than those of HTPE/N100, although curing reaction of the HTPE/TDI system is faster and more complete, as seen from FTIR spectra. Besides, the tensile strength of HTPE/N100 based propellant attains the maximum value of 0.64 MPa at NCO/OH ratio of 1.4, while the maximum XLD value of 6.5× 10−5 mol⋅cm−3 was obtained at the same time. The XLD is well correlated in tensile strength with the variation of NCO/OH, that suggests regulation of XLD value may be an effective way to optimize the curing conditions for improving mechanical properties of HTPE/isocyanate‐based propellants. [ABSTRACT FROM AUTHOR]

Epoxy/polysufone (PSF) composites cured with 4,4'‐diaminodiphenyl sulfone (DDS) and 4,4'‐diaminodiphenyl methane (DDM) were fabricated, and the effect of dual curing reaction of diamines with epoxy on morphology, mechanical, and thermal performance was investigated. DSC results indicated that DDM was more reactive than DDS and the activation energy decreased with the rising of DDM content. Structures with small domain size at the early stage of phase separation were fixed by the fast epoxy‐DDM reaction. When the DDM content was elevated to a high level, large dual structures were changed to fine bicontinuous structures, which was favorable to improve the mechanical property. The mechanical performance of epoxy composites was enhanced and the maximum values were achieved when the DDM/DDS ratio was located at 75/25 (PSF/DDS0.25‐DDM0.75). The flexural and tensile strength relative to epoxy/DDM system were enhanced more than those relative to epoxy/DDS, while the increase in toughness was the opposite. TGA measurement showed that thermal stability of epoxy/PSF composites was improved because of the restricting effect of continuous PSF domains on thermal motion of epoxy. DMA analysis exhibited two relaxation peaks for PSF/DDS0.25‐DDM0.75, which could be attributed to the formation of phase separated morphology and epoxy network with different cross‐link density. [ABSTRACT FROM AUTHOR]

Gels were obtained from resol type phenolic resins, with resorcinol, formaldehyde and lignin as precursors. Thermal response was evaluated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and curing kinetics were determined from the SDTA curves using Flynn-Wall-Ozawa and Friedman iso-conversional models. Additionally, it was used Fourier transform infrared spectroscopy (FTIR) to evaluate the progress of the curing reaction. These analyzes were performed for two gels, one of them prepared with lignin (lignin resin), and a reference (resorcinol resin). Lignin resins tend to be more thermally stable than resorcinol resins. Average values found for activation energy of the curing processes are 55.07 kJ mol−1 and 60.60 kJ mol−1 for resorcinol resin and lignin resins respectively using Flynn-Wall-Ozawa method; values of 51.94 kJ mol−1 and 53.14 kJ mol−1 were obtained using Friedman method. It was possible to conclude that the lignin affects positively the thermal stability of the resin; the curing reaction takes place in the first six hours and the Flynn-Wall-Ozawa model fits better. [ABSTRACT FROM AUTHOR]

ABSTRACT A uniform dispersion of reactants is necessary to achieve a complete reaction involving multicomponents. In this study, we have examined the role of plasticizer in the reaction of two seemingly unlikely reactants: a highly crystalline hexamethylenetetramine (HMTA) and a strongly hydrogen bonded phenol formaldehyde resin. By combining information from NMR, infrared spectroscopy and differential scanning calorimetry, we were able to determine the role of specific intermolecular interactions necessary for the plasticizer to dissolve the highly crystalline HMTA and to plasticize the phenol formaldehyde resin in this crosslinking reaction. The presence of the plasticizer increased the segmental mobility, disrupted the hydrogen bonded matrix, and freed the hydroxyl units, which further increased the solubility of the HMTA. Both the endothermic and exothermic transitions are accounted for in the calorimetric data obtained. For the first time, it is possible to obtain the effective molar ratio of each component needed to complete the crosslinking reaction efficiently. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1519-1526 [ABSTRACT FROM AUTHOR]

ABSTRACT This study demonstrates that the curing reaction of thermosetting polymers, in particular, epoxy resins cured with aliphatic amines, can be characterized by different multiple-quantum (MQ) NMR experiments performed in low-field spectrometers. Measurements of the curing reaction at 40 °C, 70 °C, and 100 °C are carried out to obtain the kinetic parameters like induction time, vitrification time, polymerization rate, and activation energy being consistent with data obtained by other traditional and complementary techniques. Besides, it is demonstrated that 1H MQ-NMR spectroscopy is a successful approach to overcome the experimental challenge arising from the characterization of high dipolar-coupled polymers to study the network structure and segmental dynamics of thermosetting polymer networks. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1324-1332 [ABSTRACT FROM AUTHOR]

Octaepoxysilsesquioxane (POSS-Ep) was first synthesized by the hydrolysis and condensation of γ-[(2,3)-epoxypropoxy]propyltrimethoxysilicane (KH-560) with the presence of ethanol and HCl at 55°C for 72 h. Then, it was cured with 4,4′-diaminodiphenylsulfone (DDS) and methylnadic anhydride (MNA), respectively. The curing reactions between POSS-Ep and DDS or MNA were investigated by FTIR. Thermal stability of the cured nanocomposites was studied by TGA. The micromophologies of the obtained hybrids were observed by SEM. FTIR results show that POSS-Ep can be cured completely with DDS or MNA to obtain the final organic-inorganic (O-I) hybrids after the same experimental curing cycle: 120°C/2 h + 140°C/2 h + 160°C/2 h + 180°C/2 h + 200°C/2 h. TGA results show that POSS-Ep/DDS hybrid displays better thermal stability than that of POSS-Ep/MNA hybrid. Initial thermal degradation temperature (Tdi) of POSS-Ep/DDS hybrid is 420°C, 195°C higher than that of POSS-Ep/MNA (225°C). SEM images of the fracture surfaces of the hybrids suggest the cured POSS-Ep possesses good mechanical properties. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]