In Situ Formation of Silica Nanoparticles Decorated with Well-Defined Homopolymers and Block Copolymers

Abstract

Grafting non-polar polymer chains on the surface of polar nanoparticles (e.g., silica) is an effective way to enhance particle/matrix interactions and thus promote their homogeneous dispersion within a non-polar matrix, which leads to improved mechanical properties. Current grafting methods have not yet produced nanoparticles with well-defined polymers on the surface and high grafting density. Here, we employed anionic polymerization high vacuum techniques to synthesize ω-triethoxysilyl polystyrene (PS-TEOS) and PS-b-PI macromonomers followed by hydrolysis/condensation of macromonomers, leading to the in situ formation of grafted (grafting through) silica nanoparticles with either PS or polystyrene-b-polyisoprene (PS-b-PI) chains. The molecular characteristics of the precursors PS-TEOS and PS-b-PI-TEOS were determined by proton nuclear magnetic resonance, size exclusion chromatography, and matrix-assisted laser desorption/ionization time-of-flight. The formation of PS (PS@SiO 2 NPs) and PS-b-PI (PS-b-PI@SiO 2 NPs) nanoparticles was verified by Fourier transform infrared spectroscopy, 29 Si solid-state NMR, transmission electron microscopy, thermogravimetric analysis, and dynamic light scattering. Blends of PS@SiO 2 with commercially available PS and PS-b-PI@SiO 2 with anionically synthesized thermoplastic elastomer (PS-b-PI-b-PS) were obtained either in melt by extrusion or in solution by evaporation. The role of polymer@SiO 2 on the mechanical properties and morphological features of the matrices was examined by tensile testing and scanning electron microscopy. The proposed general method controls the molecular weight, chemical composition, particle size, and grafting density of nanoparticles and effectively improves the mechanical characteristics of the two families of PS-based nanocomposites.

Designing Macromolecules on Nanoparticle Surfaces: In Situ Formation of Silica Grafted with Star Chains

“…In all cases, a small shoulder corresponding to (polymer chain) 2 -Si­(OEt) 2 appears at a higher retention volume (left of the SEC traces). Similar findings on end-capping with TEOS were found in our previous study (with linear polymers), where two living polymeric chains were terminated with one molecule of TEOS, as proved by SEC and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectroscopy Figure shows the 1 H NMR (500 MHz, CDCl 3 , δ in ppm) spectrum of (PS 6k ) 2 PI 12k -TEOS as a representative example.…”

“…TEOS attached to the PI block experiences a less severe barrier than TEOS linked to the PS block. This phenomenon has the same explanation as in the cases of linear homo- and copolymer as reported in a previous report . TEOS connected to the PI block ((PS 6k ) 2 -PI 12k -TEOS and (PS 6k ) 2 -PI 50k -TEOS) is subject to less steric hindrance than TEOS linked to the PS block ((PS 6k ) 2 -PS 10k -TEOS and (PS 6k ) 2 - b -PI 50k -TEOS).…”

“…The weight loss of the polymer in the case of (PS 6k ) 2 PS 10k @SiO 2 (Figure a) and (PS 6k ) 2 PI 50k - b -PS 6k @SiO 2 (Figure c) is less compared to the other two cases (Figure b) since TEOS linked to the PS block experiences more steric hindrance than TEOS attached to the PI block, ((PS 6k ) 2 PI 12k @SiO 2 and (PS 6k ) 2 PI 50k @SiO 2 , respectively). This phenomenon has the same explanation as in our previous study, where we compared PS@SiO 2 and PS -b- PI@SiO 2 . The length of the PI block (third arm attached to SiO 2 NPs) also affects the weight loss and, subsequently, the grafting ratio.…”

“…The HNPs or polymer brush-grafted particles comprise a broad range of nanostructured hybrid materials since the brush layer may consist of a neutral or a charged polymer, a flexible or a rigid polymer, and a single- or multicomponent polymer system. , In general, there are two strategies to synthesize HNPs: (i) the grafting-from method (surface-initiated polymerization), where the polymer chains grow from a surface-anchored initiator, and (ii) the grafting-to method, where end-functionalized polymer chains are grafted to the functionalized surface . In addition to these strategies, our group recently reported another method for the in situ formation of silica nanoparticles grafted with polymers, which was also employed in this study.…”

“…Benicewicz et al synthesized TPEs of poly­(styrene -block- ( n -butyl acrylate)) (PS -b- PBA) grafted silica NPs by surface-initiated RAFT polymerization . Our group recently reported the synthesis of TPEs through an in situ formation of PS -b- PI-grafted silica NPs, utilizing anionic polymerization, termination with TEOS, and subsequent hydrolysis/condensation reaction . The increased number of chain entanglements with the TPE matrix makes the star polymer on the surface of SiO 2 NPs a more promising material when used as a nanofiller compared to its linear counterpart.…”