Polybenzoxazine Aerogels. 1. High-Yield Room-Temperature Acid-Catalyzed Synthesis of Robust Monoliths, Oxidative Aromatization, and Conversion to Microporous Carbons

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• 作者：Shruti Mahadik-Khanolkar ; Suraj Donthula ; Chariklia Sotiriou-Leventis ; Nicholas Leventis
• 刊名：Chemistry of Materials
• 出版年：2014
• 出版时间：February 11, 2014
• 年：2014
• 卷：26
• 期：3
• 页码：1303-1317
• 全文大小：917K
• ISSN：1520-5002

文摘

We describe a new room-temperature HCl-catalyzed method for the synthesis of polybenzoxazine (PBO) aerogels from bisphenol A, formaldehyde, and aniline that cuts the typical multiday high-temperature (鈮?30 掳C) route to a few hours. The new materials are studied comparatively to those from heat-induced polymerization, and both types are evaluated as precursors of carbon (C-) aerogels. In addition to the ortho-phenolic position of bisphenol A, the HCl-catalyzed process engages the para position of the aniline moieties leading to a higher degree of cross-linking. Thereby, the resulting aerogels consist of smaller particles with higher mesoporosity, higher surface areas (up to 72 m² g^鈥?), and lower thermal conductivities (down to 0.071 W m^鈥? K^鈥?) than their thermally polymerized counterparts (corresponding best values: 64 m² g^鈥? and 0.091 W m^鈥? K^鈥?, respectively). It is also reported that the carbonization efficiency (up to 61% w/w), the nanomorphology, and the pore structure of the resulting C-aerogels depend critically on a prior curing step of as-prepared PBO aerogels at 200 掳C in the air. According to spectroscopic evidence and CHN analysis, curing at 200 掳C in air oxidizes the 鈭扖H₂鈥?bridges along the polymeric backbone and subsequently fuses aromatic rings (see Abstract Graphic) in analogy to transformations during carbonization processing of polyacrylonitrile. C-aerogels from cured PBO aerogels are microscopically similar to their respective parent aerogels; however, they have greatly enhanced surface areas, which, for C-aerogels from HCl-catalyzed PBOs, can be as high as 520 m² g^鈥? with up to 83% of that attributed to newly created micropores. The acid-catalyzed route is used in the next article for the synthesis of iron oxide/PBO interpenetrating networks as precursors of iron(0) aerogels.