Influence of the Norbornene Anchor Group in Ru-Mediated Ring-Opening Metathesis Polymerization: Synthesis of Bottlebrush Polymers
Influence of the Norbornene Anchor Group in Ru-Mediated Ring-Opening Metathesis Polymerization: Synthesis of Bottlebrush Polymers
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DOI：
10.1021/acs.macromol.3c00214
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发表时间：
2023-05
期刊：
影响因子：
5.5
通讯作者：
Samantha J. Scannelli;Mohammed Alaboalirat;Diego Troya;John B. Matson
中科院分区：
文献类型：
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作者：
Samantha J. Scannelli;Mohammed Alaboalirat;Diego Troya;John B. Matson
由Grubbs的第三代催化剂[G3，（H2 IMes）（Cl）2（pyr）2 RuCHPh]介导的开环易位聚合（ROMP）被广泛用于通过大分子单体（MM）的聚合来制备瓶刷聚合物，所述大分子单体（MM）通常是用α-烯烃官能化的低分子量聚合物。该策略被称为接枝通过方法，其需要高度的活性特征（“活性”）以形成轮廓分明的瓶刷聚合物。在此，我们研究了不同的锚基团，一系列的原子连接的可聚合的聚苯乙烯侧链的单元，在一系列的exo-聚苯乙烯嵌段共聚物的开环易位聚合中的活性的影响。首先，我们使用密度泛函理论方法计算了含有五种不同锚基团的MM结构的HOMO和HOMO/LUMO能隙，发现这些能隙跨越10 kcal/mol的范围。然后，我们对目标主链聚合度（Nbb）为100的每种MM进行动力学实验，以在相同条件下测量增长速率常数（kp，obs）。HOMO能量与测量的kp，obsvalues之间出现了正相关性，揭示了五个MM之间kp，obsvalues的7倍变化，表明锚群之间存在不同程度的活力。一系列针对Nbb值范围从100到2000的研究进一步强调了这些差异：具有高kp，obs值的双金属在高目标Nbb值下达到了更高的转化率，具有较低的分散度（D_p），而不是具有较低kp，obs值的双金属。最后，我们通过将MM等分试样连续五次注入催化剂溶液中，在两个极端下使用聚合物评价了瓶刷五嵌段共聚物的合成，允许在下一次注入之前聚合每个嵌段。与最低kpanchor组相比，具有最高kpanchor组的MM在每个步骤的MM转化率更高，并且每个块的D_（max）值更低。总之，这些研究突出了锚基团如何显著影响ROMP中的活性和活性，这对于合成精确的瓶刷（共）聚合物至关重要。
Ring-opening metathesis polymerization (ROMP) mediated by Grubbs’ third-generation catalyst [G3, (H2IMes)(Cl)2(pyr)2RuCHPh] is widely used to make bottlebrush polymers by polymerization of a macromonomer (MM), typically a low molecular weight polymer functionalized with a norbornene. Termed the grafting-through method, this strategy requires a high degree of living character (“livingness”) to form well-defined bottlebrush polymers. Here, we studied how various anchor groups, the series of atoms connecting the polymerizable norbornene unit to the polymer side-chain, affect livingness in ROMP in a series ofexo-norbornene polystyrene MMs. First, we calculated the HOMO and HOMO/LUMO gap energies of MM structures containing five different anchor groups using density functional theory methods, finding that these energies spanned a range of 10 kcal/mol. We then performed kinetics experiments on each MM with target backbone degrees of polymerization (Nbb) of 100 to measure the propagation rate constant (kp,obs) under identical conditions. A positive correlation between the HOMO energy and measuredkp,obsvalues emerged, revealing a 7-fold variation inkp,obsvalues across the five MMs, suggesting different degrees of livingness among the anchor groups. A series of studies targetingNbbvalues ranging from 100 to 2000 further highlighted these differences: The MMs with highkp,obsvalues reached higher conversions at high targetNbbvalues with lower dispersities (D̵) than the MMs with lowerkp,obsvalues. Finally, we evaluated the synthesis of bottlebrush pentablock copolymers using the MMs at the two extremes by injecting an MM aliquot into a catalyst solution five consecutive times, allowing for polymerization of each block before the next injection. MM conversion at each step was higher, and theD̵values for each block were lower for the MM with the highestkpanchor group compared to the lowestkpanchor group. Taken together, these studies highlight how the anchor group dramatically affects bothkpand livingness in ROMP, which is crucial for the synthesis of precise bottlebrush (co)polymers.