Towards the next development of vitrimers: Recent key topics for the practical application and understanding of the fundamental physics

Vitrimers have emerged as an innovative class of functional cross-linked polymers, providing recyclability, healability, and post-cured malleability without distinct flow. These features are attributed to the relaxation and diffusion of network strands through associative bond exchanges within the network. Significant progress has been made in investigating the chemical library and new functionalities, along with comprehensive studies on fundamental physics, including relaxation and rheological characteristics. Despite a rapid increase in research publications over the past decade, critical challenges remain in practical applications, particularly regarding preparation protocols, control of physical properties, and the development of analytical techniques. Unlike existing reviews focusing on vitrimer design and basic features, this article highlights recent crucial topics, such as vitrimer transformation from commodity polymers, the trade-off between processability and mechanical performance, and the control/analysis of stress relaxation time and topology freezing temperature, and an understanding of rheological properties, based on experimental, simulation, and theoretical studies. The transformation using commodity polymers could introduce a novel upcycling technique. The trade-off issues propose unique vitrimer designs utilizing phase-separated structures and post-molding curing. Moreover, given the strong correlation between relaxation/rheological properties and processability/recyclability/healability, their control and analysis are vital for both foundational physics and practical applications. Throughout the article, we provide insights and pose new open questions for the next development of vitrimer materials.