Composition-Orientation Induced Mechanical Synergy in Nanoparticle Brushes with Grafted Gradient Copolymers

Abstract

Gradient poly(methyl methacrylate/ n -butyl acrylate) copolymers, P(MMA/BA), with various compositional ratios, were grafted from surface-modified silica nanoparticles (SiO 2 - g -PMMA- grad -PBA) via complete conversion surface-initiated activator regenerated by electron transfer (SI-ARGET) atom transfer radical polymerization (ATRP). Miniemulsion as the reaction medium effectively confined the interparticle brush coupling within micellar compartments, preventing macroscopic gelation and enabling complete conversion. Isolation of dispersed and gelled fractions revealed dispersed particle brushes to feature a higher Young’s modulus, toughness, and ultimate strain compared with those of the “gel” counterparts. Upon purification, brush nanoparticles from the dispersed phase formed uniform microstructures. Uniaxial tension testing revealed a “mechanical synergy” for copolymers with MMA/BA = 3:2 molar ratio to concurrently exhibit higher toughness and stiffness. When compared with linear analogues of similar composition, the brush nanoparticles with gradient copolymers had better mechanical properties, attributed to the synergistic effects of the combination of composition and propagation orientation, highlighting the significance of architectural design for tethered brush layers of such hybrid materials.

Robust Miniemulsion PhotoATRP Driven by Red and Near-Infrared Light

“…Importantly, the RDRP process can be controlled by external stimuli, such as redox reagents (e.g., tin compounds, ascorbic acid), enzymes, , ultrasound, , electric current, − or light. − Among these, light has emerged as a particularly promising approach due to relatively milder reaction conditions, spatiotemporal control, and convenient setup. − Previous efforts on the photoinduced RDRP (photoRDRP) in dispersed media include (inverse) microemulsion, miniemulsion, − emulsion, − and dispersion (Scheme A). − For instance, photoATRP in emulsion can be initiated through the in situ generation of the ATRP activator [Cu I /L] + (where L is an ATRP ligand). This could be achieved by either UV irradiation (370 nm) or electron transfer from an excited photocatalyst (PC) under blue light (460 nm), reducing [X–Cu II /L] + (where X = Br or Cl).…”