Thermoset polymers from renewable resources are actively pursued via thiol-related cross-linking chemistries. Most strategies lead to limited interchain interactions and strong chemical linkages, and thus, the networks exhibit inferior mechanical performance and are difficult to recycle for further use. In this study, the reaction between thiol and oxazoline groups exhibits a high selectivity to generate thiol ether amide when catalyzed by 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU). Oxazoline-functionalized monomers are prepared from methyl vanillate and cross-linked with polymercaptans via thiol-oxazoline ring-opening addition reaction. The introduced amide groups significantly enhanced the mechanical properties compared with those networks without amide groups. Further, the amide-containing networks demonstrate improved water-absorption capability, transforming the networks into hydroplastic materials, while “hydration–drying” cycles minimally impacted their physical properties. The selective thiol-oxazoline ring-opening addition reaction herein imparts polar amide groups to thermosets, enabling an efficient strategy toward enhanced chain interactions and recyclable use through hydroplastic processing.