Mengyue Wang, Chenjing Gong, Junyang Sun, Junbo Hou, Bin Yan
Abstract The development of high-performance biobased polyester adhesives has primarily focused on mechanical reinforcement, while the relationship between adhesive performance and polymer microstructure, particularly the role of weakly polar groups, remains underexplored. Here, we construct polyester systems with precisely tuned methoxy content from vanillin-derived monomers to elucidate the regulatory role of weakly polar methoxy groups in polymer thermodynamics and metal adhesion. Methoxy incorporation effectively suppressed crystallization, inducing a transition from a highly crystalline, high-modulus state to an amorphous, low-modulus state (Tg = 24 °C). Interestingly, this weakening of bulk strength unexpectedly strengthened interfacial adhesion: the dual-methoxy system achieved a lap shear strength of 12.46 MPa on iron, surpassing the methoxy-free counterpart (3.71 MPa). Copolymerization experiments further demonstrated that by adjusting the ratio of methoxy-free to methoxy monomers, the crystallinity, mechanical properties, and adhesion strength (ranging from 3 to 15 MPa) of the polyesters can be systematically tuned over a wide range, validating the feasibility of methoxy groups as a structural switch for modulating adhesion performance. Molecular simulations revealed that methoxy groups enhance interfacial interaction with metals by increasing the polymer’s negative electrostatic potential and binding energy. This work establishes a new strategy for optimizing adhesion through crystalline-to-amorphous transition regulated by weakly polar groups, offering a molecular design perspective for tunable biobased polyester adhesives.