Preparation of Supramolecular Extenders with Precise Chain Lengths via Iterative Synthesis and Their Applications in Polyurethane Elastomers

In this study, we synthesized a dual-functional building intermediate, 4-(3,3-diethyl-2,4-dioxoazetidin-1-yl)benzoyl chloride (DEDA-BC), from readily available starting materials, including 4-isocyanatobenzoyl chloride and p-tolyl isocyanate. In its iterative syntheses of hard segments, we first treated the highly reactive acid chloride of DEDA-BC with the monoamine (aniline) or the diamine (4,4'-methylenedianiline, 4,4'-MDA) to form first-generation azetidien-2,4-dione intermediates. We then reacted these derivatives with 4-aminobenzylamine at the more-selective azetidine-2,4-dione group of DEDA-BC to form the first-generation of benzyl amine extenders. Using this alternating method, we obtained high yields of supramolecular extenders of various chain lengths (n = 1-3) in a systematic manner, without the need for tedious purification steps, under catalyst-free conditions. The mono- and diamine extenders with numbers of repeating units ranging from one to three were synthesized precisely through this new iterative synthetic approach. The molar mass increases between each generation were 365 g mol(-1) for the monoamine series and 730 g mol(-1) for the diamine series. The three generations of supramolecular extenders possessed the distinctive characteristics of multiple hydrogen bonding moieties and narrow molecular weight distributions. Their gelation phenomena in THF revealed that these amine extenders underwent supramolecular assembly, through intermolecular hydrogen bonding, to form organogels. We used these well-defined extenders with various chain lengths in the preparation of polyurethane (PU) elastomers. Small-angle X-ray scattering revealed well-defined microdomains in the morphologies of the PU elastomers presenting multiply hydrogen-bonded terminal groups. The tensile and thermal properties of the prepared PUs were dependent on the effects of the content of hard segments, the chain length, and the strength of hydrogen bonding.