Iterative synthesis of extenders of uniform chain lengths for making thermo-reversible polyurethane supramolecules
Journal
Macromolecules
Journal Volume
41
Journal Issue
3
Pages
682-690
Date Issued
2008
Author(s)
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 (Tg). Thermal degradation temperatures (Td) of both TRPUs and extenders increase with increasing hard-segment chain lengths. Different degrees of phase-segregation 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.
SDGs
Type
journal article