Copolymers of N-vinylbenzyl N-methyl pyrrolidinium chloride (VBMPC) and methyl methacrylate, PVBMPC-co-poly(methyl methacrylate) (PMMA), were synthesized by free-radical copolymerization and proved to be prone to crosslinking as a result of the reaction of methyl ester groups with benzyl methyl pyrrolidinium chloride (BMPC) moieties at temperatures higher than 110 degrees C. When the VBMPC content was lower than 20 wt %, these copolymers were miscible with homo-PMMA. Blends of homo-PMMA and PVBMPC-co-PMMA fully could be cured above 150 degrees C, when the molecular weight of PMMA exceeded 10,000 and the VBMPC content of the copolymer was higher than 5 wt %. This reaction was carried out to crosslink selectively the PMMA microdomains of PMMA-b-poly(isooctyl acrylate) (PIOA)-b-PMMA (MIM) triblock copolymers to explain the mechanism for the mechanical failure of fully (meth)acrylic thermoplastic elastomers. Comparison of the ultimate tensile properties of MIM block copolymers, when the dispersed PMMA phases and PIOA matrix were crosslinked, led to the conclusion that the ductile failure of the hard PMMA microdomains rather than the elastic failure of the PIOA matrix was the reason for the mechanical failure of MIM triblocks.