Microstructure modulated dynamics of main-chain giant molecules with exact chain-length and tunable chemical interaction

The field of polymer science has witnessed a paradigm shift from traditional polymers to giant molecules, which possess well-defined structures and discrete molecular weights. These giant molecules, constructed from precisely synthesized building blocks, offer unique opportunities to explore the relationship between molecular architecture and macroscopic properties. This study investigates the microstructure-modulated dynamics of main-chain giant molecules constructed from double-decker silsesquioxane (DDSQ) and polyhedral oligomeric silsesquioxane (POSS) building blocks. A series of giant molecules with exact chain lengths and tunable chain ends were synthesized using thiol-maleimide Michael addition reactions and an iterative "deprotection-addition" strategy. Structural and thermal analysis revealed that homopolymers and vinyl-terminated molecules exhibited amorphous features in their melt states, while carboxylic acid-terminated molecules showed evidence of microphase separation. Rheological characterization demonstrated that homopolymers and vinyl-terminated molecules exhibited unentangled, liquid-like dynamics, whereas carboxylic acid-terminated molecules displayed Zimm-like melt characteristics or pronounced elastic plateau modulus at low frequencies, indicating the formation of physically cross-linked network structures stabilized by intermolecular interactions. This research highlights that chain length and chain-end chemistry significantly govern the hierarchical assembly and viscoelastic behavior of main-chain giant molecules, offering a powerful strategy for engineering novel nanomaterials with tailored mechanical properties through precise molecular design and chain-end functionalization.