Combining multiple hydrogen bonds and boronic ester chemistry towards mechanically robust and creep resisting elastomer vitrimer

Abstract

Vitrimers circumvent the trade-off between the covalent crosslinking and malleability for polymers, making them ideal candidates for the design of reconfigurable polymer networks. However, it's extremely arduous to access elastomer vitrimers both strong in strength and creep resisting at service. Herein, to solve this conundrum, we have designed and synthesized a series of vitrimer networks by combining multiple hydrogen bonds (H-bonds) and boronic ester bonds into styrene butadiene rubber (SBR). Particularly, SBR is firstly modified by 2-ureido-4-[1H]-pyrimidinone (UPy) and subsequently crosslinked by dimercapto-borate. With a combining of π-π stacking of the UPy rings and the lateral multiple H-bonds between two ureidos in structure, the grafted UPy moieties tend to aggregate to form microphase separated structure. UPy aggregations are functional as sacrificial units and enhance the strength of the rubber vitrimers through reversible breaking and reforming events. Moreover, the UPy aggregations in hard domains make the segment mobility more confined and retard the topology rearrangement, as a result, the dimensional stability at service temperature is elevated. However, the malleability of the rubber vitrimers is hardly affected as the UPy aggregations are dissociated at elevated temperatures.