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

Abstract

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.

Hydrogen-bonded supramolecular polyurethanes

“…This ultimately conferred an element of shape recovery properties to the material. Further studies have employed supramolecular UPy‐terminated PUs in polymerization‐induced phase separation, whilst a range of other end groups capable of hydrogen bonding interactions have been employed for material assembly …”

Tuning chain extender structure to prepare high-performance thermoplastic polyurethane elastomers

“…This is the rst thermoplastic polyurethane elastomers with such high thermostability and excellent mechanical properties, compared to the present reported PUs. 7,12,19,50 Furthermore, the comprehensive performance of such pure polyurethane is even superior to many polyurethane-based composite polymers.…”

Synthesis and evaluation of alkoxylated-ether diols of hydroquinone with different chain-lengths as extenders in segmented polyurethanes

“…These hard segments act as thermo-reversible physical crosslinking sites providing the characteristic thermoplastic and elastomeric behaviours for TPU. [3] Furthermore, strong evidence has indicated that chain-length and dispersity of molecular weight of hard segments play significant roles in affecting the performance of TPU, such as mechanical and thermal properties [4][5][6][7][8][9] due to the formation of different morphological sizes and crystalline structures. [10][11][12][13][14] TPUs with a narrow dispersity in molecular weight generally show a higher and preferred elastic modulus, a less temperature-dependent modulus between the T g of the soft segment and the T m of the hard segments.…”

“…[9,[19][20][21][22][23] Nevertheless, to our knowledge, all the methods reported so far have their drawbacks. Harthcock [20] and his co-workers had to use a cumbersome gel-permeation chromatogram process to isolate individual MDI-butanediol urethane extenders of uniform chain length from random product mixtures to demonstrate their effects.…”

“…Harrell et al [21] synthesized mono-dispersed hard segment with uniform chain-length, but the prepared urethane intermediates did not possess any multiple hydrogen-bonding sites to introduce into TPU. Our laboratory [9,23] reported successful preparation of supramolecular extenders with precise chain lengths via iterative synthesis. However, the systems used azetidine-2,4-dione as the intermediate to produce malonamide/(urethane urea) diamine hard segments which are differing from the majority of polyurethane intermediates.…”