A covalent adaptable network (CAN) elastomer with a well-defined network structure was fabricated by end-linking monodisperse star polymers via associative dynamic covalent bonds (DCBs). Monodisperse 4-arm star-shaped polyesters with vinyl end groups were synthesized and end-linked by an olefin metathesis reaction, yielding an elastomer with a uniform chain length between cross-links. The well-defined network structure endowed the elastomer with good mechanical properties. The remaining C═C bonds in the network could exchange via olefin metathesis, rendering the network structure reconfigurable. As a result, the elastomer showed stress relaxation and was thermally reprocessable. Moreover, the elastomer was chemically degradable into un-cross-linked polymers under mild conditions through C═C bond exchange. This study demonstrates mechanical robustness and dynamicity in rubbery materials through the combination of a well-defined network structure and associative DCBs.
Cross-linking a blend of linear and ring polymers creates a new topology-based dual-network elastomer in which the two components differ significantly in their topology. We use molecular simulations and topological analysis to examine key mechanical properties as functions of ring polymer volume fraction ϕR. For ϕR < ϕR*, where the rings begin to overlap, the network shear modulus G and the maximum stretch ratio λp are weakly dependent on ϕR. For ϕR > ϕR*, entanglements trapped in the network are diluted as the rings overlap, leading to a significant decrease in G and an increase in λp with increasing ϕR. The peak tensile stress, σp, exhibits a maximum around ϕR*, indicating an enhancement of network strength due to the stronger cohesion from the entanglements between linear and ring polymers.
Current research on the antifouling mechanisms of “electrically neutral” polymer brushes predominantly emphasizes thermodynamically unfavorable short-range interactions. However, our study reveals the critical importance of long-range interactions. By utilizing zwitterionic poly(carboxybetaine methacrylate) (PCBMA) and nonionic poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) brushes as model systems, we employed total internal reflection microscopy (TIRM) to directly measure interactions with contaminants. Surprisingly, even seemingly neutral polymers exhibit significant electrostatic interactions with nearby contaminants─a fact that has been largely overlooked in this field. Our findings challenge the prevailing assumption of charge absence on surfaces grafted with antifouling polymer brushes and investigate how external stimuli (such as ionic strength and polymer conformation) affect these long-range interactions. In conclusion, this study presents a novel approach to exploring long-range interactions near polymer-grafted surfaces, offering valuable insights for the development of antifouling materials and biomedical applications in the future.
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