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This study reports the utilization of controlled radical polymerization as a tool for controlling the stimuli-responsive capabilities of graphene oxide (GO) based hybrid systems. Various polymer brushes with controlled molecular weight and narrow molecular weight distribution were grafted from the GO surface by surface-initiated atom transfer radical polymerization (SI-ATRP). The modification of GO with poly(n-butyl methacrylate) (PBMA), poly(glycidyl methacrylate) (PGMA), poly(trimethylsilyloxyethyl methacrylate) (PHEMATMS) and poly(methyl methacrylate) (PMMA) was confirmed by thermogravimetric analysis (TGA) coupled with online Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Various grafting densities of GO-based materials were investigated, and conductivity was elucidated using a four-point probe method. Raman shift and XPS were used to confirm the reduction of surface properties of the GO particles during SI-ATRP. The contact angle measurements indicated the changes in the compatibility of GOs with silicone oil, depending on the structure of the grafted polymer chains. The compatibility of the GOs with poly(dimethylsiloxane) was also investigated using steady shear rheology. The tunability of the electrorheological, as well as the photo-actuation capability, was investigated. It was shown that in addition to the modification of conductivity, the dipole moment of the pendant groups of the grafted polymer chains also plays an important role in the electrorheological (ER) performance. The compatibility of the particles with the polymer matrix, and thus proper particles dispersibility, is the most important factor for the photo-actuation efficiency. The plasticizing effect of the GO-polymer hybrid filler also has a crucial impact on the matrix stiffness and thus the ability to reversibly respond to the external light stimulation. [ABSTRACT FROM AUTHOR]

In real technological processes, both shear and elongational flow is present. The material properties may differ significantly under both types of flow. Hence, they both define the final morphology and thus properties of the materials. In this work, the morphology of immiscible blends containing polymer hybrid particles was related to extensional rheological properties for the first time. The effect of various lengths of polymer brushes grafted from graphene oxide particles (GO) surface was investigated. As a polymer matrix the immiscible blend of poly(methyl methacrylate)/styrene- co -acrylonitrile (PMMA/SAN) was used. Thus the poly(methyl methacrylate) (PMMA) brushes grafted from GO (GO- g -PMMA) with various number average molar masses (M n) of PMMA brushes with respect to chain entanglement limit of freely dispersed PMMA were prepared. The extensional rheological properties were affected by M n of PMMA brushes, while the rheological properties in shear were unchanged. Transmission electron microscopy revealed the compatibilization effect for short densely grafted brushes with M n of 10,300 g/mol, as smaller domains were observed. On the contrary, the higher M n PMMA brushes facilitated coalescence. With increasing length of brushes, the elongational viscosity at low elongation rates (∼< 0.1 s−1) decreased, which facilitated the coalescence. The increase of viscosity at higher elongation rates (∼> 0.1 s−1) was not sufficient enough to cause fiber breakup and thus elongated domains were formed. [Display omitted] • Rheology in elongation flow was used to evaluate the compatibilization effect of particle polymer hybrids for first time. • Graphene oxide grafted with poly(methyl methacrylate) brushes of various length for immiscible polymer blends were used. • The GO- g -PMMA improved the particle dispersion, and location was affected with DP of brushes. • The negligible effect of PMMA brushes DP was observed by shear rheology. • The elongation flow showed significant differences, especially at low strain rates. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is a wide bandgap semiconductor material that has attracted widespread interest as particle filler in polymer nanocomposite materials. However, its applications have been hindered by the limited dispersibility and surface-modification techniques. Herein, three distinct approaches for the synthesis of polymer-tethered ZnO hybrid materials are compared in terms of uniformity and yield of the particle-brush product: “grafting-from”, “grafting-onto”, and “grafted-copolymer template” methods. In the “grafting-from” method, pristine ZnO nanoparticles (NP) were first functionalized with atom transfer radical polymerization (ATRP) initiators followed by grafting-from process to form poly(methyl methacrylate) (PMMA) or poly(styrene- co -acrylonitrile) (PSAN) tethered polymer chains. In the “grafting-onto” method, PMMA- b -PAA (poly[acrylic acid]) and PSAN- b -PAA diblock copolymers were prepared and attached onto the surface of ZnO NPs using sonication bath. For the “grafted-copolymer template” method, PSAN- b -P t BA-Br (poly[ tert -butyl acrylate]-Br) macroinitiators were crosslinked with divinylbenzene (DVB) to form PSAN- b -P t BA-PDVB core-shell star polymers. After hydrolysis to form PSAN- b -PAA-PDVB star polymers, the functional stars were used as polymer templates for the synthesis of ZnO NPs within the PAA-core of the stars. Core-shell molecular bottlebrushes with PAA- b -PS block-copolymer side chains were also used as anisotropic analogues of star template to prepared worm-like ZnO particles. Several ZnO precursors, zinc nitrite, zinc 2-ethylhexanoate, and zinc acetate were evaluated as precursors of ZnO. Conditions were identified that enable the synthesis of polymer-tethered ZnO with excellent size uniformity and dispersion characteristics using the star-template method. [ABSTRACT FROM AUTHOR]

A new concept of utilization of particle-polymer hybrids as multifunctional additives for polymer blends was introduced in this study. Graphene oxide particles with short densely grafted polystyrene brushes (GO- g -PS) were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP). Melt rheology studies revealed that GO- g -PS suppressed the phase separation of miscible poly(methyl methacrylate)/poly(styrene- co -acrylonitrile) (PMMA/SAN) blends. The studies suggested specific interactions of GO- g -PS with the PMMA phase and this was confirmed based on calculations of activation energies of segmental relaxations by broadband dielectric spectroscopy (BDS). These unusual interactions of GO- g -PS with PMMA phase were assigned to the specific and precise architecture of the GO- g -PS particles as well as chemical nature of PS polymer brushes. The short chains of PMMA and PS provide miscibility originating from UCST behavior of PMMA/PS blend of short polymer chains. Additionally, BDS also revealed improved charge transport in PMMA/SAN blend in presence of GO- g -PS hybrid. Image 1 • New multifunctional additives for miscible polymer blends were introduced. • The graphene oxide plates grafted with short dense polystyrene brushes were used. • The increase of LCST of the PMMA/SAN blends enriched with GO-g-PS was observed at very low filler loading. • The improved interactions of synthesized hybrid particles with PMMA component of miscible blend were proved. [ABSTRACT FROM AUTHOR]