Bulky Rigid Substituent to Enhance the Chain Mobility of Cellulose for Bio‐Degradable Thermoplastics

Bulky substituents typically cause an increase in glass temperature transition (Tg) of polymers and the deterioration of their thermoplastic properties. Herein, it is demonstrated that ortho‐substituted bulky aromatic groups can reduce the Tg of macromolecules chains. The introduction of aromatic groups with ortho substituents can markedly improve the free volume of macromolecules and reduce the interchain binding energy, thus promoting segmental mobility. Additionally, a direct correlation is established between the volume of ortho‐substituents and Tg depression, where bulkier groups induced more pronounced thermal transitions. Based on this principle, non‐thermoplastic biomass materials are successfully converted into processable thermoplastics. The incorporation of bulky rigid 2‐methyl benzoate group or 2‐trifluoromethyl benzoate group into natural cellulose (Tg = 300 °C) greatly reduces the Tg of the cellulosic materials to 130 or 101 °C, respectively, enabling thermal processing below the degradation thresholds. The obtained cellulose materials are readily processed to various biodegradable plastic objects, melt‐spun fibers, and thermal transfer ink by eco‐friendly thermoplastic processing methods, indicating a breakthrough in sustainable material engineering. This novel principle to regulate Tg enriches the polymer theory and also establishes a generalized strategy for developing next‐generation biorenewable thermoplastics.