Unusual Stress Upturn in Elastomers Prepared Using Macro Cross‐Linkers with Multiple Vinyl Side Groups

In this study, the unique tensile properties of acrylate elastomers prepared using macro cross‐linker polymers with multiple vinyl side groups are analyzed. For the preparation of the macro cross‐linker, poly(ethyl acrylate) copolymers bearing hydroxy functional groups are synthesized, followed by the hydroxy‐isocyanate reaction with 2‐isocyanatoethyl acrylate. Subsequently, the elastomers samples are prepared by UV polymerization of ethyl acrylate in the presence of the macro cross‐linkers. The tensile properties of the elastomers in the small elongation region are similar to those of typical elastomers prepared using divinyl cross‐linkers, whereas the stress upturn in the large elongation region is considerably different. The stress upturn varies based on the fraction of vinyl side groups in the macro cross‐linkers, whereas stress in the small elongation region remains unchanged. These properties are analyzed using various theoretical models. The results reveal that there is artificial inhomogeneity in the cross‐link density for samples prepared by the macro cross‐linkers, where the short poly(ethyl acrylate) strands inside the macro cross‐linker limit the overall chain stretchability. On the whole, this study demonstrates a new method for tuning elastomer properties, especially at large deformation. Unusual tensile properties with distinct stress upturn behaviors are demonstrated for elastomers prepared using macro cross‐linker polymers with multiple vinyl side groups. These elastomers are much different from classical elastomers prepared using divinyl cross‐linkers, and behave like bimodal elastomers. The present study thus provides a new method for tuning tensile properties of elastomers, especially at large deformation.