Ultra-high-molecular-weight (UHMW) polymers can display outstanding properties; however, it is challenging to synthesize UHMW polymers by using external free radical initiators. To address this, here, we report the ration design and adoption of B-alkylcatecholborane (RBCat) as a radical initiator in controlled radical polymerization in the presence of a chain-transfer agent. The autoxidation of RBCat with one alkyl substituent generates only one alkyl radical. The oxygen is incorporated and stored in the oxidized form (ROOB-Cat) that slowly releases the alkyl radical. The rationally designed alkyl radical is proposed to preferentially activate the chain-transfer agent (CTA) and grow the polymer chain from CTA, so limited free polymer chains are formed from the initiating alkyl radicals. Polymerizations of (meth)acrylates are achieved with narrow molecular weight distribution (Р= 1.10) and predetermined molecular weights even in a UHMW range (up to 3 million). The successful chain extension of UHMW indicates the high degree of control of the polymerization.

超高分子量（UHMW）聚合物可以显示出出色的性能；然而，通过使用外部自由基引发剂来合成UHMW聚合物具有挑战性。为了解决这个问题，我们在此报告B的定量设计和采用-在链转移剂存在下受控自由基聚合中作为自由基引发剂的-烷基儿茶酚硼烷（RBCat）。RBCat与一个烷基取代基的自氧化仅产生一个烷基。氧以缓慢释放烷基的氧化形式（ROOB-Cat）结合并存储。提出了合理设计的烷基以优先激活链转移剂（CTA）并从CTA增长聚合物链，因此由引发的烷基形成有限的自由聚合物链。（甲基）丙烯酸酯的聚合具有窄的分子量分布（Р= 1.10）和预定的分子量，甚至在UHMW范围内（最高300万）。UHMW的成功扩链表明对聚合的高度控制。