Direct Preparation of High Surface Area Mesoporous SiC-Based Ceramic by Pyrolysis of a Self-Assembled Polycarbosilane-block-Polystyrene Diblock Copolymer

Direct pyrolysis of a self-assembled inorganic-organic block copolymer can be a promising route for fabricating the ordered ceramic nanostructures based on the achievements of organic-organic block copolymers. Here we report the synthesis of a novel polycarbosilane-block-polystyrene diblock copolymer by ring-opening living anionic polymerization in a THF and n-hexane solvent system at similar to 48 degrees C. The resulting block copolymer revealed phase-separation behavior in the nanoscale to form a self-assembled nanostructure that was converted to a mesoporous ceramic phase after heating at 800 degrees C. The pyrolyzed ceramic product exhibited well-ordered mesoporous SiC-based ceramic structures with a high BET surface area of 1325 m(2) g(-1) and an average mesopore size of 7.8 nm containing a large amount of micropores.X112930sciescopu

Well-Ordered Nanostructure SiC Ceramic Derived from Self-Assembly of Polycarbosilane-Block-Poly(methyl methacrylate) Diblock Copolymer

The fabrication of SiC ceramic materials with an ordered nanostructure through the direct pyrolysis of a self-assembled inorganic-organic block copolymer has generally been unsuccessful even though the versatile processibility has been demonstrated with organic-organic block copolymers. Here we report the synthesis of a novel polycarbosilane-block-poly(methyl methacrylate) diblock copolymer through ring-opening living anionic polymerization in a THF and n-hexane solvent system at -48 degrees C. The resulting block copolymer exhibited phase-separation behavior on the nanoscale to form a self-assembled nanostructure that was converted to a mesoporous ceramic after heating at 800 degrees C. The characterization of diblock copolymer is simultaneously investigated by GPC, and NMR analyses. The self-assembly of diblock copolymer is characterized by small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). In particular, the preparation of high-temperature-stable nanostructured silicon carbide and mesoporous silicon carbide ceramic directed from cross-linked polycarbosilane blocks with a high ceramic yield are described, which exhibits well-oriented nanostructures with the size in a range of 4-10 nm. These exciting results have a great potential to open a new field for the generation of nanostructured non-oxide ceramic or metal-ceramic materials for a broad class of applications.X117sciescopu

Controlled/living radical polymerization of vinylcyclicsilazane by RAFT process and their block copolymers

High molecular weight poly(vinyl)silazane were synthesized successfully by reversible addition fragmentation chain transfer (RAFT) polymerization in toluene at 120 degrees C, using dithiocarbamate derivatives and 2,2&apos;-azobis-isobutyrylnitrile (AIBN) as the RAFT agents and thermal initiator, respectively. The polymerization of a vinyl-cyclicsilazane oligomer with 82.5% conversion was readily controlled to increase the molecular weight from 1000 to 12,000 g/mol with a narrow polydispersity <1.5. The resulting polymer showed a high ceramic yield of 70 wt % at 1000 degrees C. Moreover, the approach was extended successfully to the synthesis of poly(vinyl)silazane-block-polystyrene as an inorganic-organic diblock copolymer. (C) 2008 Wiley Periodicals, Inc.X1199sciescopu

Synthesis of Inorganic-Organic Diblock Copolymer as a Precursor of Ordered Mesoporous SiCN Ceramic

A novel poly(vinyl)silazane-block-polystyrene diblock copolymer is successfully synthesized by living free-radical polymerization via a reversible addition fragmentation chain transfer (RAFT) route (see figure). The obtained diblock copolymer, having an inorganic volume fraction of 0.69, leads to phase-separation at the nanoscale to form an ordered nanostructure, which is converted to well-ordered mesoporous SiCN ceramic after heating at 800 degrees C and maintained up to 1400 degrees C.X114343sciescopu

Microwave assisted synthesis of high molecular weight polyvinylsilazane via RAFT process

The microwave-assisted synthesis of high molecular weight polyvinylsilazane (H-PVSZ) leads to a narrow molecular weight distribution at accelerated polymerization rates under controlled/living polymerization, while retaining the excellent controllability offered by reversible addition fragmentation chain transfer (RAFT) polymerization in a thermal reaction process. Under microwave irradiation, higher molecular weight H-PVSZ (6250 vs. 4370) was obtained with higher conversion (86.7 vs. 30.1%) than under conventional heating through a simple 3 h reaction of vinylcyclicsilazane with a molecular weight of 314 in the presence of dithiocarbamate derivatives (RAFT agent) and 2,2&apos;-azobis-isobutyronitrile (AIBN, thermal initiator). H-PVSZ with a well-controlled high molecular weight is useful for synthesizing inorganic-organic diblock copolymer polyvinylsilazane-block-polystyrene (PVSZ-b-PS) with a higher molecular weight and lower polydispersity than by conventional heating of the PVSZ-derived product. (C) 2009 Elsevier Ltd. All rights reserved.X1116sciescopu