Simultaneous Improvement of Tensile Strength and Elongation: An Unprecedented Observation in the Case of Hydroxyl Terminated Polybutadiene Polyurethanes

Abstract

Chemical modifications of hydroxyl terminated polybutadiene (HTPB) with hydrogen bond forming functionalities were used as tactics to improve both tensile strength and elongation of polyurethanes (PUs) simultaneously. PUs were prepared using various diisocyanates with modified HTPB in which dinitrobenzene (DNB) groups are attached to terminal carbon atoms. The spectroscopic studies revealed the presence of an additional hydrogen bonding network between DNB and the urethane backbone which resulted into supramolecular cross-linking and was found to be responsible for significant improvement in mechanical properties of HTPB-DNB-PUs. Also, substantial improvement of elongation at break was observed in the case of HTPB-DNB-PUs. Small angle X-ray scattering (SAXS) and thermodynamical studies indicated a strong segmental mixing between the hard and soft segments of HTPB-DNB-PUs. Growth of partial crystalline character in HTPB-DNB-PUs was believed to be responsible for "fibrous-assembly" morphology. In summary, modification of HTPB induced extra cross-linking through supramolecular hydrogen bonding which in turn concurrently enhanced both strength and elongation of PUs.

Preparation and Characterization of Fluorinated Hydrophobic UV-Crosslinkable Thiol-Ene Polyurethane Coatings

“…The bands at 3343 and 1527 cm −1 were the characteristic peaks of -NH- [38]. In curve A, the disappearance of the isocyanate band at 2270 cm −1 [37] and the appearance of the -NH-band of urethane linkage at 3343 cm −1 confirmed the formation of HTPU. Figure 2 shows the 1 H NMR spectra of HTPB and HTPU represented by A and B, respectively.…”

“…The characteristic peak at 967 cm −1 of HTPB (curve C) corresponded to the trans olefin structure [36]. The band at 1712 cm −1 of prepolymer (curve B) corresponded to the stretching C=O vibration of the -NH-COO-group [37], and the appearance of a band at 967 cm −1 indicated the chemical reaction between -OH of HTPB and -NCO of IPDI. The bands at 3343 and 1527 cm −1 were the characteristic peaks of -NH- [38].…”

Triazine functionalized hydroxyl terminated polybutadiene polyurethane: Influence of triazine structure

“…The stoichiometric ratio between the functional groups (ÀNCO/ÀOH) was maintained constant and equal to 1:1 for all PUs synthesis. The moles of eOH functionality are calculated from the hydroxyl values of HTPB and modified HTPB [42,43,46]. It is to be noted that all the reaction conditions and curing conditions for the preparation of all twelve PUs are exactly identical.…”

“…Several approaches have been established in literature by which either 3 b or s b of PUs can be improved. For example, the increase in NCO/OH ratio or hard segment content (HSC) often enhances the tensile strength; on the other hand increase in the soft segment content results into higher ε b [42,43,46]. However, it is very difficult to improve both tensile strength (s b ) and elongation at break ( 3 b ) simultaneously.…”

“…Very recently, an experiment to improve both the strength and elongation of HTPB based PUs with the help of an aromatic functional moiety namely dinitrobenzene (DNB) which is chemically attached at the terminal carbons of HTPB and is capable of introducing hydrogen bonding between the hard and soft segments of HTPB-PUs was successful [42,43]. It was proved that the nitro functionality of dinitrobenzene is responsible for segmental mixing through hydrogen bonding interactions which in turn improves tensile strength and elongation simultaneously.…”