In-situ decorating diene-rubber with carbamyl maleamic handles as sacrificial units toward network reinforcement

The decoration of sacrificial units (SUs) into rubber network has gained momentum as a non-filling alternative toward efficient network reinforcement. However, most established methods, including the copolymerization with SUs-containing monomers or the post-modification of rubber backbone, still suffer from the multi-step and time-consuming backbone preparation with poor designability. In this work, we proposed a facile and practical strategy to achieve efficient network reinforcement through in-situ decorating isoprene rubber (IR) network with N-carbamyl maleamic acid (NCMA) as SUs. Model compound vulcanization experiment demonstrated that during sulfur vulcanization, the poly/disulfides in active sulfurating agents or crosslinking precursors can cleave into reactive sulfur radicals, which subsequently proceeded radical addition reaction with the unsaturated NCMA. The decorated carbamyl maleamic handles can spontaneously form multiple hydrogen-bonding linkages to serve as SUs. Upon deformation, the reversible detachment/reattachment of the SUs will smooth out the local stress concentration, but also facilitate the orientation of network chains. Therefore, as the NCMA loading increases, the onset of strain-induced crystallization and the overall crystallinity of the obtained IR network are simultaneously promoted, giving rise to a gradual increase in the tensile modulus (∼80 %) of the system. By virtue of the rich variety, commercial availability and facile structural tunability of maleamic acid-derivatives, we envisage that the present study can open up a novel strategy to achieve in-situ decoration of rubber with various functional handles toward efficient network reinforcement and functionalization.