In this article, we describe the synthesis and self-assembly of novel Janus bottlebrushes with cellulose as a polymeric backbone. The cellulosic Janus bottlebrushes, bearing poly(ε-caprolactone) ...(PCL) and polystyrene (PS) branches at the C-2,3 and C-6 positions of anhydroglucose units, respectively, were successfully prepared using a bulky
p
-methoxytrityl protecting group and by combining the “grafting-from” ring-opening polymerization of ε-caprolactone with the “grafting-to” click chemistry of PS. The degree of substitution of PCL at the C-2,3 positions was estimated to be 1.5, whereas values of 0.64–0.84 were estimated for the C-6 position of PSs with different molecular weights (number-average molecular weight = 4.0, 9.2, or 16 kg mol
−1
), depending on the length of the PS graft. The Janus bottlebrushes (PS/PCL = 50:50 v/v) self-assembled to form a lamellar microdomain structure comprising three layers (amorphous PCL, crystalline PCL, and amorphous PS layers), as characterized by small-angle X-ray scattering and transmission electron microscopy. The interlamellar distance was approximately 30 nm, depending on the length of the PS graft. The results illustrate that cellulosic polymeric backbones for Janus bottlebrushes can exhibit microscale morphologies, potentially leading to the development of polymers with new morphologies and functionalities.
Graphic abstract
Concentrated polymer brushes (CPBs) synthesized by advanced surface-initiated controlled radical polymerization have received increasing attention in the tribological field because CPBs in good ...solvents exhibit superlow friction phenomena under macroscopic severe sliding conditions. To realize tribological applications of CPBs, an understanding of the wear mechanisms of CPBs is required to develop a method to enhance their durability. In this study, an operando tribo-Raman spectroscopic experiment, which is an effective approach for revealing the wear mechanisms of tribo-materials, was conducted on the frictional interface between a polymethyl methacrylate (PMMA)-CPB and a bearing steel ball immersed in an ionic liquid (IL), which is a good solvent for PMMA-CPBs. From the operando tribo-Raman results, the concentrations and molecular structures of the PMMA-CPBs and IL at the frictional interface were found to be constantly changing with the sliding cycles during operation. Moreover, their time-dependent changes strongly affected the wear process and superlow friction phenomena of the PMMA-CPB lubricated with the IL. Consequently, our results suggest that controlling the degree of swelling of CPBs at frictional interface is an effective approach for realizing a durable-superlow frictional tribo-system of CPBs.
•Tribological phenomena of CPB–steel tribo-systems in ionic liquids were investigated.•The Tribo-Raman method was conducted to reveal the tribological phenomena.•The conformation of CPB chains and ILs were changed during friction test.•The concentration of CPB chains and ILs decreased during friction test.•Their conformation is a key factor for achieving superlubricity of the system.
Concentrated Polymer Brushes (CPBs) have great potential to improve tribological properties under severe sliding conditions, even at the macroscopic scale, and thus are expected to apply to ...mechanical sliding components. However, the durability of CPBs has remained as a challenge for industrial applications. Here, we focused on a combination of CPBs and surface texturing technology to increase their durability. In this work, the effects of surface texturing, such as geometrical patterns on the durability of CPBs under severe sliding conditions, were investigated. The results demonstrate that applying a surface texture onto a substrate of CPBs can effectively improve the friction durability of CPBs because the polymers inside the textures, which have a locally milder contact condition, are prone to survive. By applying an appropriate surface texture, we achieved up to a 36% increase in durability.
•Concentrated Polymer Brushes (CPBs) have excellent frictional properties (lower than 0.03 in friction coefficient).•Applying a groove texture onto the substrate of CPBs increases their friction durability up to 36% compared to nontextured CPBs.
This article introduces the new family of living radical polymerizations with germanium (Ge), tin (Sn), phosphorus (P), and nitrogen (N) catalysts which we recently developed. The polymerizations are ...based on a new reversible activation mechanism, Reversible chain Transfer (RT) catalysis. Low-polydispersity polymers are obtained in the homopolymerizations and random and block copolymerizations of styrene, methyl methacrylate, and functional methacrylates. The background, performance, and kinetic features of the polymerizations are described. Attractive features of the catalysts include their high reactivity, low toxicity (Ge, P, and N), low cost (P and N), and ease of handling (robustness).
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Concentrated polymer brushes (CPBs) are promising soft-material coatings for improving tribological properties under severe sliding conditions, even in the macroscopic scale. Therefore, they are ...expected to be applied to mechanical sliding components. However, the durability of CPBs has remained challenging for industrial applications. Previous studies revealed that applying a groove texture to the CPB substrate is effective in improving the durability of CPBs. In order to achieve further improvement of durability of CPBs, we attempted to apply nano-periodic structures, whereas the groove texture applied in previous studies has widths and depths in micrometres. In this study, the effect of the nano-periodic structure in addition to the groove texture applied to the CPB substrate on the durability of CPB is investigated. The results demonstrate a significant improvement in the durability of CPBs by up to 90% compared with non-textured CPB when an appropriate nano-periodic structure is applied (i.e. a nano-periodic structure oriented parallel to the groove texture).
Graphic Abstract
The aim of this study is to fabricate a contrast agent for magnetic resonance imaging (MRI) by using hybrid particles composed of a core of iron oxide magnetite (Fe3O4) nanoparticles and a shell of ...hydrophilic polymer brush synthesized by surface-initiated (SI) living radical polymerization. To achieve this, Fe3O4 nanoparticles were surface-modified with initiating groups for atom transfer radical polymerization (ATRP) via a ligand-exchange reaction in the presence of a triethoxysilane derivative having an ATRP initiation site. The ATRP-initiator-functionalized Fe3O4 nanoparticles were used for performing the SI-ATRP of methyl methacrylate to demonstrate the ability of the synthesized nanoparticles to produce well-defined polymer brushes on their surfaces. The polymerization proceeded in a living fashion so as to produce graft polymers with targeted molecular weights and narrow molecular weight distribution. The average graft density was estimated to be as high as 0.7 chains/nm(2), which indicates the formation of so-called concentrated polymer brushes on the Fe3O4 nanoparticles. Dynamic light scattering and transmission electron microscope observations of the hybrid nanoparticles revealed their uniformity and dispersibility in solvents to be excellent. A similar polymerization process was conducted using a hydrophilic monomer, poly(ethylene glycol) methyl ether methacrylate (PEGMA), to prepare Fe3O4 nanoparticles grafted with poly(PEGMA) brushes. The resultant hybrid nanoparticles showed excellent dispersibility in aqueous media including physiological conditions without causing any aggregations. The blood clearance and biodistribution of the hybrid particles were investigated by intravenously injecting particles labeled with a radio isotope, (125)I, into mice. It was found that some hybrid particles exhibited an excellently prolonged circulation lifetime in the blood with a half-life of about 24 h. When such hybrid particles were injected intravenously into a tumor-bearing mouse, they preferentially accumulated in the tumor tissues owing to the so-called enhanced permeability and retention effect. The tumor-targeted delivery was visualized by a T2-enhaced MRI measurement.
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