Multifunctional polyurethane-vitrimers completely based on transcarbamoylation of carbamates: thermally-induced dual-shape memory effect and self-welding

Abstract

The polyurethane-vitrimers with the properties of reprocessing, thermally-induced dual-shape memory effect and self-welding would reduce waste and accumulated pollution of crosslinking polymer.

Carbon Nanotubes‐Polyurethane Vitrimer Nanocomposites with the Ability of Surface Welding Controlled by Heat and Near‐Infrared Light

“…As a demonstration, we synthesized CNTs‐PUVs by chemical reaction of the hexamethylene diisocyanate (HDI) with polyethylene glycol (PEG, M n = 2000) and castor oil (CO) in the presence of dibutyltin dilaurate (DBTDL) as a catalyst for transcarbamoylation and CNTs as functional filler (Figure A). There were six samples with different content of CNTs ranging from 0 to 1 wt%, and based on our group previous work, all samples' content of catalyst was 3 wt%. The FTIR spectroscopy of CNTs‐PUVs and PUV is shown in Figure A.…”

“…Additionally, in some vitrimer systems, solvent must be added to achieve an almost perfect welding . Besides, spatial and remote control of interface welding is similarly demanded for its development under certain circumstances, for example, our group synthesized a series of PUVs that only could be welded by heat before, which greatly restricted its application . However, Yang et al presented CNT‐vitrimer epoxy materials that realized photowelding of epoxy, inspiring us to explore the possibilities of remote welding control in other vitrimer systems.…”

“…In this study, based on our previous work, to break through the restriction of surface welding of thermosetting materials, we prepared a carbon nanotubes‐polyurethane vitrimer (CNTs‐PUV) nanocomposite system with an ability of pressure‐free surface welding totally based on transcarbamoylation of carbamates that have already been studied systematically by Xie and co‐workers ( Figure B) via classical polyurethane chemistry. Thanks to the photothermal conversion effect of CNTs, we find that this system has a great property of photowelding which is first reported in polyurethane vitrimer system and make the remote‐control welding of thermosets possible.…”

Reactivity of urethanes at high temperature: Transurethanization and side reactions

“…Quantification of the side reactions helps to improve the synthesis and processing conditions of PUs. Turning to more advanced topics, transcarbamoylation (reaction 2 in Scheme ) is the key process in the functioning of PU vitrimers . Vitrimers are covalently linked networks, which behave like duromers at low temperatures .…”

“…Vitrimers may self‐heal. PU‐vitrimers rearranging their topology by transcarbamoylation were reported to have similar properties as the existing thermoset PUs —but can be reprocessed at high temperatures . Chemical recycling of PU starting from depolymerization and urethane bond exchange reactions at high temperatures was reported to be promising and effective .…”