The preparation of discrete and stereochemically defined polymers is essential for establishing reliable structure-function relationships and enabling the rational design of functional synthetic macromolecules. Discrete oligomers with precisely defined molar mass and sequence can be accessed by combining controlled polymerization with purification; however, the functional diversity of such oligomers remains limited, because both polymerization and high-resolution separation are typically compatible only with selected functionalities. Herein, we report a versatile route to discrete oligoacrylamides bearing diverse functional groups via postpolymerization amidation of discrete oligo(N-succinimidyl acrylates) (oligo(NSA)) as common activated-ester precursors. Discrete di-, tri-, and tetra-NSA were prepared on a subgram scale by reversible addition-fragmentation chain-transfer (RAFT) polymerization followed by normal-phase flash chromatography and subsequently converted into 16 discrete oligoacrylamides bearing seven different functional groups. As an additional demonstration of stereochemical control, all four stereoisomers of di(NSA) were isolated by chiral chromatography and transformed to the corresponding stereochemically defined acrylamide dimers. This postpolymerization diversification strategy expands the structural diversity accessible for discrete oligomers and provides a practical platform for constructing well-defined oligomer libraries for downstream molecular design.
Ultralow-cross-linked microgels serve as powerful model systems for investigating structure-rheology relationships in soft colloidal suspensions. Using precipitation polymerization, we obtain both self-cross-linked microgels with a weakly cross-linked core, surrounded by an ultrasoft corona (ULC), and regular cross-linked (RC) microgels. ULC microgel suspensions exhibit distinctive rheological responses in crowded conditions. Their linear viscoelastic behavior shares features with critical-like gels, characterized by G' ∼ G″ ∼ ωn. Large-amplitude-oscillatory-shear measurements reveal a solid-liquid transition reminiscent of polymeric networks lacking a G″ overshoot during yielding. Stress-shear strain rate measurements further reveal shear-thinning with a power-law behavior at low shear strain rates, σ ∼ γ̇∼0.25. We attribute this behavior to a fine-tuned balance between polymeric and colloidal contributions. This rheological response to crowding establishes ULC microgels as emergent soft nanocolloids with potential biological relevance, particularly as analogues for the heterogeneity in mechanical softness (compressibility) observed in cell membranes.
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：