We unveil universal correlations between architectural parameters and nonlinear elastic properties of brush polymer networks. A comprehensive library of poly(n-butyl acrylate), poly(dimethylsiloxane), and polyisobutylene brush networks was synthesized with systematically varied side chain length (∼n sc ), grafting density (∼n g −1 ), and backbone degree of polymerization between cross-links (n x ). This allowed experimental verification of theoretical scaling relationships between mechanical properties (shear modulus and strain-stiffening), architectural parameters [n sc , n g , n x ], and microstructure from in situ small-angle X-ray scattering in both comb and bottlebrush conformational regimes. These results can be used as a foundation for the programmable design of mechanically diverse solvent-free elastic materials. Article pubs.acs.org/Macromolecules

Pressure sensitive adhesives (PSAs) are ubiquitous materials within a spectrum that span from office supplies to biomedical devices. Currently, the ability of PSAs to meet the needs of these diverse applications relies on trial-and-error mixing of assorted chemicals and polymers, which inherently entails property imprecision and variance over time due to component migration and leaching. Herein, we develop a precise additive-free PSA design platform that predictably leverages polymer network architecture to empower comprehensive control over adhesive performance. Utilizing the chemical universality of brush-like elastomers, we encode work of adhesion ranging 5 orders of magnitude with a single polymer chemistry by coordinating brush architectural parameters–side chain length and grafting density. Lessons from this design-by-architecture approach are essential for future implementation of AI machinery in molecular engineering of both cured and thermoplastic PSAs incorporated into everyday use.

Brush-like thermoplastic elastomers combine softness, firmness, strength, and damping on par with soft tissues, which is vital for biomedical device and adhesive applications.

Polymer networks with brush-like (comb or bottlebrush) strands can have mechanical properties similar to biological tissues and can swell to larger volumes than their linear chain counterparts. We use a combination of the Flory−Rehner approach, scaling analysis, molecular dynamics simulations, and experimental data for poly(n-butyl acrylate) (PBA) networks swollen in toluene to elucidate the effect of brush strand architecture on the equilibrium swelling ratio, Q eq , the modulus of the swollen gel, G gel (Q eq ), and its relationship with the nonlinear modulus of the dry network, G(Q eq ). Analysis of simulation data and experimental results for PBA gels demonstrates that the gel shear modulus monotonically decreases with increasing equilibrium swelling ratio as, which is consistent with a θ-solvent-like swelling behavior. There is a significant effect of the degree of polymerization n sc and grafting density 1/n g of the side chains on the gel modulus that manifests as mechanically diverse gels with the same solvent content. This unique behavior is explained by the architecture-controlled stiffening of the brush strands due to the swelling of the side chains in the gel state. In the framework of a scaling model, the effective Kuhn length of the swollen strands, b K,s , can be expressed in terms of the Kuhn length in the dry state, b K , and the ratio of shear modulus calculated in the framework of the Flory−Rehner approach, G gel, to the gel modulus G gel (Q eq ) such that b K,s ≈ b K G gel FR (Q eq )/G gel (Q eq ). The Kuhn length obtained from this analysis highlights different mechanisms of swollen brush rigidity.

Controlled incorporation of nitrogen into macromolecular skeletons is a long-standing challenge whose resolution would enable the preparation of soft materials with the scalability of man-made plastics and functionality of Nature's proteins. Nylons and polyurethanes notwithstanding, nitrogen-rich polymer backbones remain scarce, and their synthesis typically lacks precision. Here we report a strategy that begins to address this limitation founded on a mechanistic discovery: ring-opening metathesis polymerization (ROMP) of carbodiimides followed by carbodiimide derivatization. An iridium guanidinate complex was found to initiate and catalyze ROMP of N-aryl and N-alkyl cyclic carbodiimides. Nucleophilic addition to the resulting polycarbodiimides enabled the preparation of polyureas, polythioureas, and polyguanidinates with varied architectures. This work advances the foundations of metathesis chemistry and opens the door to systematic investigations of structure-folding-property relationships in nitrogen-rich macromolecules.