Overlooked Impact of Interchain H-Bonding between Cross-Links on the Mechanical Properties of Thermoset Polyurethane Elastomers

Abstract

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).

Polyurethane-Based Blend Membrane Containing Polycarbonate for Gas Separation: Compatibility Analysis, Microstructure Evaluation, and CO2 Separation Performance

“…Based on Figure a, a distinct peak corresponding to cross-linking is observed at a temperature of 173.83 °C. This cross-linking phenomenon is attributed to the linear structure of the synthesized PU, where the soft segment undergoes cross-linking through the formation of cross-links facilitated by the presence of hydrogen bonding sites. − The FTIR spectrum of the synthesized polymer exhibits shifted and newly formed peaks compared to non-cross-linked PU, providing further evidence for this phenomenon. Notably, peaks at the wavenumbers of 635, 781, 1220, and 1463 cm –1 (see Figure b) demonstrate the pronounced changes associated with cross-linking.…”

Polyurethane Exothermic Polymerization and Phase Change Material Thermal Delay Matching: An Approach to Reducing Fire Risks in Mining Polymer Materials

“…During the foaming process, the more ureido-potassium ester reaction of 5%EP/12P-PU enhances the branched and cross-linked strength of the polyurethane foam, which further promotes the development of pores in the material. Consequently, 5%EP/12P-PU undergoes phase change and heat absorption after the polyurethane foaming is completed, which is less destructive to the original material properties and improve the foaming multiplicity of the product …”

Polydimethylsiloxane-Based Polyurethane as the Matrix of Electrorheological Elastomers with an Adjustable Dielectric Constant and Improved Field-Active Efficiency

“…Polyurethanes (PUs) are block polymers consisting of alternating soft and hard segments: the hard segments provide structural rigidity via self-conjugation to form hard domains; the low glass transition temperature of soft segments confers flexibility. − The thermodynamic incompatibility of soft and hard segments causes PU to have a distinct microphase separation structure, and the degree of microphase separation is closely related to the mechanical properties of PU . Also, the mechanical properties of PU can be obtained by adjusting the ratio and chemical structure of both soft and hard segments. , In addition, the designability of the PU structure can be achieved by adjusting the structure and type of monomer isocyanate and polyol.…”