The role of diisocyanate structure on microphase separation of solution polymerized polyureas

• Published in: Polymer (Guilford) Vol. 55; no. 3; pp. 906 - 913
• Main Authors: He, Yong, Zhang, Xinya, Runt, James
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 12.02.2014; Elsevier
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Phase separation; Physicochemistry of polymers; Polyurea; Properties and characterization; Structure, morphology and analysis; X-ray scattering; Polyurea; X-ray scattering; Phase separation; Thermal transition; Urea polymer; Nanostructure; Experimental study; Dielectric relaxation; Organic diisocyanate; Domain structure; Aliphatic polymer; Supramolecular structure; Comparative study; Hydrogen bond
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2014.01.001

Three diisocyanates with different symmetry and planarity (2,6-TDI, 2,4-TDI and MDI) were used to synthesize polyureas with the same oligomeric polyetheramine having a molecular weight of ∼1000 g/mol. The influence of diisocyanate symmetry on the phase separated morphology, hydrogen bonding behavior, and molecular dynamics were investigated. Symmetric diisocyanate structures facilitated self-assembly of hard segments into ribbon-like domains, driven by strong bidentate hydrogen bonding. The hard domains for the 2,6-TDI polymer appear to be continuous in AFM images, while the persistence length of the hard domains in the 2,4-TDI and MDI polymers gradually decrease, and fewer hard domains are apparent with decreasing hard segment symmetry. The extent of hard/soft segment demixing, assessed from small-angle X-ray scattering, was very incomplete for all of the polyureas and is significantly influenced by hard segment structure. For the 2,4- and 2,6-TDI polyureas, two segmental relaxations were observed using dielectric relaxation spectroscopy; one arising from relatively unrestricted motion in the soft segment rich phase, and a slower process associated with segments in the soft phase constrained by their attachment to hard domains. [Display omitted]