Self-catalyzed hydrolysis upon storage of the common RAFT chain-transfer agent (CTA) 4-cyano-4-[(thiothiopropyl)sulfanyl] pentanoic acid (CTPPA) is confirmed, where the nitrile group is transformed into an amide by catalysis from the adjacent carboxylic acid moiety. The amide-CTA (APP) is found to poorly control molecular weight evolution during polymerization of two methacrylates, methyl methacrylate (MMA) and N,N-(dimethylamino)ethyl methacrylate (DMAEMA), likely due to poor reinitiation speed in the pre-equilibrium. However, when attached to a macromolecule, the impact of this amide moiety becomes insignificant and chain extension proceeds as expected with CTPPA. In light of CTPPA and similarly hydrolyzable CTAs being extensively employed for aqueous polymerizations of methacrylates, these findings highlight the importance of CTA purity when performing RAFT polymerizations.

中文翻译：

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含腈RAFT链转移剂的自催化水解及其对甲基丙烯酸单体聚合控制的影响


常见的 RAFT 链转移剂 (CTA) 4-氰基-4-[(硫硫基丙基)硫烷基]戊酸 (CTPPA) 在储存时发生自催化水解，其中腈基通过催化转化为酰胺。相邻的羧酸部分。研究发现，酰胺-CTA (APP) 在两种甲基丙烯酸酯、甲基丙烯酸甲酯 (MMA) 和甲基丙烯酸 N,N-(二甲基氨基)乙酯 (DMAEMA) 聚合过程中控制分子量变化效果不佳，这可能是由于预聚合过程中的再引发速度较差。平衡。然而，当连接到大分子上时，该酰胺部分的影响变得微不足道，并且链延伸按照 CTPPA 的预期进行。鉴于 CTPPA 和类似的可水解 CTA 广泛用于甲基丙烯酸酯的水相聚合，这些发现强调了进行 RAFT 聚合时 CTA 纯度的重要性。