Wearable Thermal Energy Storage Polymeric Materials via the Progressive Phase Change Strategy of Crystalline Bottlebrush Polysiloxane Networks

Flexible polymeric solid–solid phase change materials (PCMs) have garnered continuous attention owing to their potential for thermal management in flexible/wearable devices and their non-leakage characteristics. However, it is still a big challenge to obtain polymeric solid–solid PCMs with both flexibility and high latent heat. In this study, bottlebrush phase change polysiloxane networks with alkyl side chains of different lengths (Si-X) are prepared through a one-step grafting cross-linking process. The influence of the length of the grafting chain on the mechanical and thermomechanical properties, phase change behavior, rheological characteristics, and thermal stability of materials is systematically studied. Furthermore, the concept of progressive phase change is proposed by cografting of crystalline side chains with multiple lengths in bottlebrush polysiloxane networks, which reduces the dense packing of crystals. The resulting network (Si-ODDT-70) exhibits excellent latent heat (ΔH_m = 128.0 J/g; ΔH_f = 129.1 J/g) and elongation at break values exceeding 200 and 450% at room and body temperatures, respectively. In addition, Si-ODDT-70 can be freely coiled, rolled, cut, and repaired with UV light at room temperature. Besides, the recyclable, stretchable/bendable, and multiresponsive phase change composites are obtained by combining the liquid metal/graphene paper with Si-ODDT-70. The first proposed cografting strategy offers a solution to unify the flexibility and high latent heat of PCMs, which will further enrich bottlebrush polymer network topology structures and guide the future design of flexible polymeric PCMs.