Experimental and modeling studies of IPDI‐based polyurea elastomers – The role of hard segment fraction

• Published in: Journal of applied polymer science Vol. 140; no. 10
• Main Authors: Tzelepis, Demetrios A., Suzuki, Jorge, Su, Yi Feng, Wang, Yiyu, Lim, Yong Chae, Zayernouri, Mohsen, Ginzburg, Valeriy V.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 10.03.2023; Wiley Subscription Services, Inc; Wiley
• Subjects: adhesive; Diamines; Diisocyanates; dynamic mechanical analysis; Elastomers; fractional calculus; Gels; hard domains; MATERIALS SCIENCE; Modelling; Polymers; polyurea; Polyureas; Qualitative analysis; Segments; time temperature superposition; Toluene; Weight
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.53592

Segmented polyureas (PUa) are industrially important class of polymers widely used in coatings, sealant, and adhesive applications. Here, we report synthesis, characterization, and modeling of Isophorone Diisocyanate‐Diethyl‐Toluene‐Diamine‐Polyether amine (IPDI‐DETDA‐PO PUa) with varied hard segment contents of 20, 30, and 40 weight percent. For each of the three materials, we study its structure and phase behavior using FTIR, DSC, and TEM, and clearly show the presence of microphase separation between the hard and soft nanodomains. We then measure the linear viscoelastic response of the PUa‐s using DMA (frequency sweeps at multiple temperatures). The DMA data are shown to obey the time‐temperature superposition. Finally, we develop a new micromechanical model describing the DMA results; the model describes a phase‐separated PUa as two “Fractional‐order Maxwell gels” branches, connected in parallel, with the first FMG branch representing the “percolated hard phase" and the second one modeling the “filled soft phase". In agreement with the earlier thermodynamic theories, the volume‐fraction of the percolated hard phase is related to the hard segment weight‐fraction (HSWF), defined as the combined mass of IPDI and DETDA normalized to the total mass of the polymer. The data and model are found to be in a good qualitative and quantitative agreement. Polyurea (PUa) adhesives have unique properties due to their nanophase‐separated morphology. Here, multiple experimental techniques (TEM and DSC) are used to elucidate the hard phase domain structure as a function of the formulation. A new micromechanical model is then proposed to describe linear viscoelasticity of the material and successfully validated based on DMA measurements.