| 查看: 478 | 回复: 1 | ||
大四写论文金虫 (正式写手)
|
[求助]
求翻译这段话
|
|
Recently, synthesis of microporous covalent organic polymers has advanced very rapidly, partly due to the urgent need for low-density porous materials for hydrogen and methane storage. Such polymers, consisting solely of light elements (H, B, C, N, O, etc.), can be constructed by a wide variety of standard synthetic strategies in organic chemistry. In extreme cases, covalent organic frameworks (COFs) with crystalline structures and high surface area can be constructed under thermodynamic control. The COFs are obtained by carefully selecting the building blocks and the conditions of their synthesis, which is carried out in a closed system to ensure reversibility of the condensation reactions;the choice of solvent appears to be very important to slow down the reversible process. In general, however, solidification of organic polymer chains results in dense,nonporous solids because such highly flexible and translationally and conformationally mobile macromolecules tend to minimize their own void volume by efficiently packing in the solid state. In addition, such polymers are mostly formed under kinetic control and irreversible conditions;hence, the formed bonds hardly rearrange into the ideal positions to achieve highly porous and ordered structures. Consequently,molecules with high rigidity and symmetry, nonplanarity,and high connectivity have been considered as suitable monomers that can frustrate the packing of the resulting polymers, and thus afford loosely packed, porous solids. Polymers of intrinsic microporosity (PIMs) formed by means of dioxane-forming reactions exhibit apparent Brunauer–Emmet–Teller (BET) specific surface areas of 500–1000 m2 g1 depending on the structure of the monomers.Hyper-cross-linked polymers are another example of porous organic polymers that can display permanent porosity because of extensive chemical cross-links that prevent the polymer chains collapsing into dense solids.The simplest networks constructed from styrenic monomers have a wide range of BET surface areas (100–2000 m2g1) that depend mainly on the degree of cross-linking and the monomers. Amorphous conjugated microporous polymers can be synthesizedwith BET surface areas in the range 500–1200 m2 g1 by means of Pd0/CuI-catalyzed Sonogashira cross-coupling. Micropore distributions of these conjugated poly(arylene ethynylene) materials could be controlled by means of the rigid node–strut topology, in particular by the average strut length,[19a,b] and this implies that order and crystallinity are not prerequisites for precise control over porosity of materials. These previous reports strongly suggest that selection of the right monomer is a critical factorto achieve synthetic porous organic polymers with high surface area and narrow pore size distribution. |
回复此楼» 猜你喜欢
282求调剂
已经有11人回复
-
本科211生物医学工程085409求调剂339分
已经有8人回复
-
材料调剂
已经有3人回复
-
284求调剂
已经有13人回复
-
385分 生物学（071000）求调剂
已经有10人回复
-
材料专硕 调剂
已经有14人回复
-
求调剂
已经有5人回复
-
306分材料与化工求调剂
已经有7人回复
-
一志愿211生物学280分 求调剂
已经有3人回复
-
086000生物与医药298调剂求助
已经有9人回复
fjtony163
版主 (文坛精英)
米米
- 翻译EPI: 386
- 应助: 361 (硕士)
- 贵宾: 6.876
- 金币: 70610.6
- 散金: 36050
- 红花: 222
- 沙发: 616
- 帖子: 21912
- 在线: 3793.7小时
- 虫号: 1397876
- 注册: 2011-09-11
- 专业: 遗传学研究新技术与方法
- 管辖: 论文翻译
2楼2015-03-08 13:44:07
