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请问有人做过聚氯甲基苯乙烯的后交联反应吗
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大家好，之前通过悬浮聚合制备了一些聚氯甲基苯乙烯微球，其中加入20%二乙烯基苯作为交联剂（P-VBC-DVB）。粒径大概0.3mm~1mm 现在打算以FeCl3作为催化剂进行后交联（postcrosslinking）,使氯甲基反应掉，从而合成出具有高比表面积的超高交联聚合物小球（hypercrosslinked polymer bead）。 现在采用的方式是：高分子小球在氮气保护下在2氯乙烷中溶胀2小时，然后把无水氯化铁和另一部分2氯甲烷加入反应器，然后继续搅拌一小时以充分分散。接着升温80度反应8小时。 补充： 1.反应原料均充分除水，反应在氮气保护下进行； 2.催化剂无水FeCl3的含量有所调整，最少是小球质量的五分之一，最多是小球质量的1.2倍 3.电热套加热，油浴加热，机械搅拌，磁子搅拌都尝试过 4.尝试过室温下直接加无水氯化铁，也尝试过冰浴下加入。 但现在的问题是所以实验结果就两种： 1.小球完全破碎 2.小球形态保存良好，但测试IR发现氯甲基峰明显还存在（尽管小球颜色已经明显变化） 请问有没有做过相同或者相似反应的同仁可以给我一些帮助或者建议呢，谢谢了！ 另外悬浮聚合通常需要用到索氏提取，那么应该是开始制备小球之后就进行还是后交联之后再做？或者需要做两次？ |
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Friedel–Crafts reaction can proceed in a rather limited number of inert solvents, such as aliphatic hydrocarbons, benzene, nitrobenzene, CS2,and chlorinated or fluorinated hydrocarbons. Among these solvents, however, only chlorinated hydrocarbons, particularly EDC, nitrobenzene, as well as cyclohexane at an elevated temperature, are suited for the synthesis of hypercrosslinked polystyrene, since they are thermodynamically good solvents for both the initial polystyrene and the final products of crosslinking. The choice of a catalyst is dictated by two main requirements: it should dissolve in the selected solvent and provide a sufficiently high rate of chemical reaction between polystyrene and a crosslinking agent. The activity of anhydrous Friedel–Crafts catalysts is well known to decrease in the following sequence: AlBr3≈AlCl3> FeCl3> SnCl4> TiCl4> ZnCl2>> BF3> HCl> H2SO4 > P2O5 AlCl3 and AlBr3 are the most active catalysts but they cause degradation of polystyrene chains. FeCl3 represents a rather strong oxidative agent, and so there always exists an anxiety for introducing some functional groups into the final products. Both AlCl3 and FeCl3 possess low solubility in the solvents suitable for the reaction. Still, FeCl3 and AlCl3 are often used to catalyze the post-crosslinking of preliminary chloromethylated styrene–DVB copolymers. The salts, though scarcely soluble in EDC, readily migrate into the swollen copolymer beads due to a fairly fast formation of a reaction complex with an aromatic species [92, 93]. A substantial shortcoming of both AlCl3 and FeCl3 is that they also catalyze the reaction of the solvent, EDC, with polystyrene [94]. SnCl4 and TiCl4 may be considered as most suitable catalysts for the post-crosslinking reaction, at least for laboratory-scale studies. Finally, hydrochloric and sulfuric acids, though catalyzing the crosslinking of polystyrene with the most reactive 1,4-dichloromethyl-2,5-dimethylbenzene [95], are too weak to provide a sufficiently high rate of the reaction. It must be emphasized here that all Friedel–Crafts catalysts are strongly hygroscopic and decompose in improperly dried solvents, although indications can be found in the literature that small traces of water or alcohols act as activating co-catalysts. In any case attention must be paid to the purity of the solvent selected for the post-crosslinking reaction. In laboratory experiments we opted, for convenience reasons, for the use of stannic tetrachloride, which dissolves in EDC, cyclohexane, and nitrobenzene, possesses sufficiently high activity at elevated temperatures, and at the same time initiates a rather smooth beginning of the reaction. |
7楼2012-04-19 15:41:49
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4楼2012-04-18 23:25:22
★ ★ ★ ★ ★
小木虫: 金币+0.5, 给个红包，谢谢回帖
zznjut: 金币+2, 欢迎交流 2012-04-19 10:00:19
zznjut: 应助指数+1 2012-04-19 10:00:28
kl5top: 金币+2, 非常感谢 2012-04-19 13:13:40
小木虫: 金币+0.5, 给个红包，谢谢回帖
zznjut: 金币+2, 欢迎交流 2012-04-19 10:00:19
zznjut: 应助指数+1 2012-04-19 10:00:28
kl5top: 金币+2, 非常感谢 2012-04-19 13:13:40
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