Iterative Synthesis of Extenders of Uniform Chain Lengths for Making Thermo-Reversible Polyurethane Supramolecules

Abstract

An efficient iterative synthesis was utilized to prepare hard-segment extenders of uniform chain lengths with multiple hydrogen-bonding sites for uses in preparation of supramolecular thermoreversible polyurethanes (TRPUs). The unique feature of our iterative synthesis is based on two alternative addition reactions to a dual-functional intermediate, 4-isocyanato-4′(3,3-diethyl-2,4-dioxoazetidino)diphenylmethane (assigned as [MIA]), where (1) the more reactive isocyanate group of [MIA] was reacted first with anilines or secondary amine group of 1-(2-aminoethyl)piperazine followed by (2) addition of a more reactive primary aliphatic amine group of 1-(2-aminoethyl)piperazine to react with the more selective azetidine-2,4-dione group of the [MIA]. With this iterative synthetic approach, three generations of supramolecular extenders were prepared, and each were added to isocyanate-prepolymers of varied chain lengths to form supramolecular "pseudo-triblock" TRPUs with a similar hard segment content of about 41%. It was found that both supramolecular extenders and their respective TRPUs showed distinctive glass transition temperatures (T g ). Thermal degradation temperatures (T d ) of both TRPUs and extenders increase with increasing hard-segment chain lengths. Different degrees of phasesegregation were present in the synthesized TRPUs and have shown to be enhanced in the same general trend. Investigations by variable-temperature FT-IR and circular scanning treatment of DSC on the TRPU [G2-41] with second generation extenders, between 25 and 180°C revealed thermal reversibility due to the increasing (at room temperature) and diminishing of hydrogen bonding (at 180°C) among the multiple hydrogen-bonding hard-segment chains. The results of SAXS analyses of TRPUs with first and second generation extenders further showed that these TRPUs formed self-assembling phase-segregated domains. The TRPU [G2-41] was found to exhibit the most prominent phase-segregation observed by SAXS with formation of uniform hard-segment domains of 40 nm. In the meantime, it also behaves like a polyurethane elastomer with a high elongation of 651% possessing the best mechanical properties found among the series. This study further demonstrated that a structural balance between uniform chain-length hard-segment extenders and their connecting soft segment play a dominant role on performances of "pseudo-triblock" polyurethane systems through molecular self-assembling.

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

“…1a and S2, † BDO-PU shows a lowest T 5% below 300 C. BDO-PU is usually unstable at temperatures higher than 230 C due to the decomposition of urethane bond and transurethane reaction, thus limits its further application. 32 Aer introducing monoFc diols as the chain extenders into PU chains, T 5% are increased to 320 C. And it can further reach to a higher T 5% of 345 C with using the bisFc as the chain extender. Meanwhile, the decomposition temperature of T max for monoFc-PU and bisFc-PU were also increased by 50 C and 70 C than the one of BDO-PU, respectively.…”

Crosslinking mechanism of supramolecular elastomers based on linear bifunctional polydimethylsiloxane oligomers

“…In recent years, the introduction of hydrogen bonds to the polymer system has been actively used to prepare novel supramolecular elastomers (SESis). [2][3][4][5][6][7] These SESis usually show some interesting properties, such as self-healing and reprocessability, because of the dynamic nature of the hydrogen bond and the special crosslinking networks, which differ from those in the vulcanizate.…”

Synthesis and properties of segmented polyurethanes with hydroquinone ether derivatives as chain extender

“…Most of these studies focused on the diisocyanate portion including diisocyanate type [11][12][13][14], hard segment length [15,16], and hard domain crystallinity [7,17]. Only a few researches have involved with chain extender structure, particularly those containing aromatic chain extender [18][19][20][21][22][23][24].…”