Reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylamide in methanol using dithioester RAFT chain-transfer agent 2a was unsuccessful due to degradation of the end group. However, this degradation was completely suppressed by the addition of rare-earth metal triflates (RMTs). As RMTs are effective for the stereoselective polymerization of acrylamides, RAFT polymerization in the presence of RMTs afforded the corresponding poly(acrylamide)s with controlled molecular weight and tacticity. The conditions allowed the synthesis of high-molecular-weight polyacrylamides with molecular weights up to 168 000, low dispersity (<1.5) and high tacticity (90% meso diad selectivity). The degradation mechanism initiated by nucleophilic attack of acrylamide on the dithioester group was experimentally clarified for the first time. As RMT is a Lewis acid, its coordination to the amide group of acrylamide reduces its nucleophilicity.

中文翻译：

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路易斯酸在防止丙烯酰胺在甲醇中的 RAFT 聚合中二硫酯休眠物质降解中的作用，从而成功地双重控制分子量和立构规整度

由于端基降解，使用二硫酯 RAFT 链转移剂2a在甲醇中进行丙烯酰胺的可逆加成断裂链转移 (RAFT) 聚合不成功。然而，添加稀土金属三氟甲磺酸盐 (RMT) 完全抑制了这种降解。由于 RMT 对丙烯酰胺的立体选择性聚合有效，因此在 RMT 存在下进行 RAFT 聚合可提供相应的具有受控分子量和立构规整度的聚（丙烯酰胺）。这些条件允许合成分子量高达 168 000、低分散性 (<1.5) 和高立构规整度 (90% meso选择性）。首次通过实验阐明了丙烯酰胺对二硫酯基的亲核攻击引发的降解机制。由于 RMT 是一种路易斯酸，它与丙烯酰胺的酰胺基团的配位降低了其亲核性。