Debromination of ATRP-made Wang soluble polymer supports
Debromination of ATRP-made Wang soluble polymer supports
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DOI：
10.1016/j.polymer.2015.02.057
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发表时间：
2015-08
期刊：
影响因子：
4.6
通讯作者：
L. Oswald;Thanh Tam Trinh;Delphine Chan-Seng;Jean‐François Lutz
中科院分区：
文献类型：
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作者：
L. Oswald;Thanh Tam Trinh;Delphine Chan-Seng;Jean‐François Lutz
本文介绍了两种简便的方法来去除原子转移自由基聚合（ATRP）制备的具有良好定义的可溶性聚合物载体的ω-端溴原子。目标可溶性支持物是线性聚苯乙烯链，其在其α链末端含有酸不稳定的对烷氧基苄基酯连接基（即Wang连接基）。这些聚合物通过ATRP使用芴基甲氧羰基（Fmoc）保护的氨基官能ATRP引发剂，即2-溴异丁酸3-（Fmoc-氨基）丙酯合成。在聚合之后和Wang官能化之前，去除ATRP制成的可溶性载体的溴原子。对两种不同的脱溴方法进行了审议。第一种方法是在氢化三烷基锡存在下还原末端烷基溴。该方法可以在聚合结束时直接应用于ATRP介质中，或者可以在纯化的聚合物样品上进行。发现后一种条件更合适。还观察到，在不存在另外的自由基引发剂的情况下使用氢化三丁基锡导致最佳结果。事实上，获得了具有受控链长、分子量分布和完全脱卤链端的明确定义的聚合物载体。第二种脱卤方法包括通过用叠氮化钠亲核取代来除去末端溴化物。然后，通过铜催化的叠氮-炔1，3-偶极Huisgen环加成反应，将形成的末端叠氮基与1-戊炔反应。这种方法也被发现是有效的制备无溴聚苯乙烯载体。在ω-链端脱溴之后，在α-链端进行Fmoc-脱保护，并且所得胺官能团与4-（羟甲基）苯氧基乙酸反应。Wang连接基的进一步酯化也是可能的。
This article describes two convenient methods for removing the ω-terminal bromine atom of well-defined soluble polymer supports prepared by atom transfer radical polymerization (ATRP). The targeted soluble supports are linear polystyrene chains that contain an acid-labile p-alkoxybenzyl ester linker (i.e. Wang linker) at their α-chain end. These polymers are synthesized by ATRP using a fluorenylmethoxycarbonyl (Fmoc)-protected amino functional ATRP initiator, namely 3-(Fmoc-amino)propyl 2-bromoisobutyrate. After polymerization and before Wang functionalization, the bromine-atom of the ATRP-made soluble supports was removed. Two different debromination approaches were considered. The first one consists in reducing the terminal alkyl bromide in the presence of a trialkyltin hydride. This method can be applied directly in the ATRP medium at the end of the polymerization or can be performed on a purified polymer sample. The latter conditions were found to be more suitable. It was also observed that the use of tributyltin hydride in the absence of additional radical initiator led to the best results. Indeed, well-defined polymer supports with controlled chain-length, molecular weight distribution and fully dehalogenated chain-ends were obtained. The second dehalogenation approach consisted in removing the terminal bromide by nucleophilic substitution with sodium azide. Afterwards, the formed terminal azide group was reacted with 1-pentyne by copper-catalyzed azide-alkyne 1, 3-dipolar Huisgen cycloaddition. This method was also found to be valid for preparing bromine-free polystyrene supports. After ω-chain-end debromination, Fmoc-deprotection was performed on the α-chain-end and the resulting amine function was reacted with 4-(hydroxymethyl)phenoxyacetic acid. Further esterification of the Wang linker is also possible.