Regioblock copolymers of single alkenes hold great promise for modifying the properties of polymer materials but remain scarce due to the lack of viable synthetic methodologies. Here we describe a method for switching the regioselectivity of the cationic yttrium-catalyzed polymerization of conjugated dienes during chain growth, which leads to the formation of a series of di- and multiregioblock homo/mixed-copolymers with different properties from isoprene and myrcene. Mechanistic data demonstrate that the amidinate yttrium active species [L^bYPIP^3,4]⁺ (L^b = [PhC(NC₆H₄ⁱPr₂-2,6)₂]⁻) changes to the tetramethylaluminate yttrium active center {L^sYPIP^3,4}⁺ (L^s = [AlMe₄]⁻) in situ by amidinate ligand transfer in the presence of AlMe₃. The transformation of active species switches the regioselectivity from 3,4- to cis-1,4 polymerization while the polymer chain keeps propagating. AlⁱBu₃ not only functions as a chain transfer agent but also plays a key role in preventing the chain termination during the amidinate transmetalation. These results highlight the versatility and potential utility of a strategy for the design and precision control of polymer structure and physical properties.

中文翻译：

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异戊二烯区域嵌段共聚：通过活性钇物种的原位辅助配体重金属化来切换区域选择性

单一烯烃的区域嵌段共聚物对于改变聚合物材料的性能具有广阔的前景，但由于缺乏可行的合成方法而仍然稀缺。在这里，我们描述了一种在链增长过程中切换阳离子钇催化的共轭二烯聚合反应的区域选择性的方法，该方法导致形成一系列具有异戊二烯和月桂烯不同性质的二-和多-区域嵌段均聚物/混合共聚物。力学数据表明，the酸钇活性物种[L ^b YPIP ^3,4 ] ⁺（L ^b = [PhC（NC ₆ H ₄ ⁱ Pr ₂ -2,6）₂ ] ^-）在存在AlMe ₃的情况下通过a基配体转移原位改变为四甲基铝酸盐钇活性中心{L ^s YPIP ^3,4 } ⁺（L ^s = [AlMe ₄ ] ^-）。活性物质的转化将区域选择性从3,4-切换为顺-1,4聚合，而聚合物链则在不断传播。人^我卜₃不仅起链转移剂的作用，而且在防止mid基金属转移过程中防止链终止中起着关键作用。这些结果突出了设计和精确控制聚合物结构和物理性能的策略的多功能性和潜在实用性。