Characterization of Phase Structures of Novel Metallo‐Polyurethanes

Abstract

Two series of chemically well-defi ned polyurethanes (PUs) have been synthesized containing two different soft segments of interest in aerospace applications. At a given soft fragment, four different hard segments (HSs) based on single diisocyanate molecules with no chain extenders have been incorporated. Both segmented PU series have been prepared by stoichiometric reactions of the macrodiol hydroxyl-terminated polybutadiene (HTPB), and a metallo-derived, this being the (ferrocenylbutyl) dimethylsilane grafted on HTPB, so-called Butacene. Those HSs are isophorone diisocyanate, toluene-2,4-diisocyanate, 4,4′-diphenyl methane diisocyanate, and hexamethylene diisocyanate. Microphase separation and morphology development have been studied at room temperature in these copolymers using Fourier transform infrared spectroscopy, analyzing the change in the relative intensities of free and hydrogen-bonded carbonyl peaks. Measurements of wide-and small-angle X-ray diffraction using synchrotron radiation allow analyzing the morphological and microstructural differences between these two series of samples. In addition, dynamic mechanical analysis and differential scanning calorimetry have been used to learn about the relaxation processes and thermal transitions that are observed in these materials and to confi rm the existence or lack of phase segregation. The knowledge of structure-property relationship is very important in these advanced organometallic PUs to get an understanding of their application as solid composite propellants binder.

Effect of hydroxyl‐terminated poly(fluoroalkyl methacrylate) main‐chain length on the microphase separation of waterborne fluorinated polyurethane

“…For WFPU‐12, the hard segments showed a peak at around 33 °C and a broader shoulder at about 77 °C. The broader shoulder may be ascribed to certain heterogeneity in long hard units . Accordingly, the difference of glass transition temperature between soft and hard segments became larger.…”

“…All the samples presented three characteristic thermal transitions. The plateau at around −50 °C corresponded to the glass transition temperature of the soft segments ( T g,s ); the other plateau at about −12 °C was ascribed to the glass transition temperature of the shortest hard segments ( T g,h ); the broad melting peak in the range 50–100 °C belonged to the short‐range order in hard segments ( T m,h ) . The enthalpy (Δ H ) of the short‐range order in hard segments was determined by the integration of the peak areas.…”

“…For WFPU-12, the hard segments showed a peak at around 33 ∘ C and a broader shoulder at about 77 ∘ C. The broader shoulder may be ascribed to certain heterogeneity in long hard units. 29 Accordingly, the difference of glass transition temperature between soft and hard segments became larger. The results showed that the introduction of fluorinated side chains into WPU and the increasing main-chain length of HTPFMA could lead to an increase of the extent of microphase separation, resulting from the increase of interactions between hard and hard segments, as discussed above for the FTIR analysis.…”

“…The analysis of hydrogen bonded C O groups using FTIR spectroscopy could provide valuable information to understand the extent of microphase separation in polyurethane. [29][30][31] The changes of the C O types in hard segments would influence the packing of molecules and, further, the crystal structure of hard segments and the extent of microphase separation between hard and soft segments. In this study, FTIR spectra were analyzed between 1600 and 1800 cm −1 by deconvolution of the C O peaks.…”

Hydroxyl Terminated Polybutadiene: Chemical Modification and Application of these Modifiers in Propellants and Explosives

“…This pre-polymer is a grafted polymer obtained by hydrosilylation of a ferrocenyl organo silicon derivative, Fe-R-SiH(CH 3 ) 2 , and the vinyl groups of HTPB (Scheme 9: Butacene®). Many studies of Butacene ® , such as application, [92,93] rheological behavior [94][95][96][97] and characterization [98] of Butacene ® -based polyurethanes have been thoroughly executed. Kurva et al [99] envisaged an application for high BR composite propellants with Butacene ® as a BR modifier by partially (10% to 50%) replacing HTPB using a TDI/IPDI bi-curing system in the ratio of 65/35.…”