Cleveland Jacob W, Choi Ji Il, Sekiya Ryoh-Suke, Cho Jinwon, Moon Hyun June, Jang Seung Soon, Jones Christopher W
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Dr., Atlanta, Georgia 30332-0100, United States.
School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Dr., Atlanta, Georgia 30332-0245, United States.
ACS Appl Mater Interfaces. 2022 Mar 9;14(9):11235-11247. doi: 10.1021/acsami.1c21738. Epub 2022 Mar 1.
This work explores the efficacy of silica/organic hybrid catalysts, where the organic component is built from linear aminopolymers appended to the silica support within the support mesopores. Specifically, the role of molecular weight and polymer chain composition in amine-bearing atom transfer radical polymerization-synthesized poly(styrene--2-(4-vinylbenzyl)isoindoline-1,3-dione) copolymers is probed in the aldol condensation of 4-nitrobenzaldehyde and acetone. Controlled polymerization produces protected amine-containing poly(styrene) chains of controlled molecular weight and dispersity, and a grafting-to thiol-ene coupling approach followed by a phthalimide deprotection step are used to covalently tether and activate the polymer hybrid catalysts prior to the catalytic reactions. Site-normalized batch kinetics are used to assess the role of polymer molecular weight and chain composition in the cooperative catalysis. Lower-molecular-weight copolymers are demonstrated to be more active than catalysts built from only molecular organic components or from higher-molecular-weight chains. Molecular dynamics simulations are used to probe the role of polymer flexibility and morphology, whereby it is determined that higher-molecular-weight hybrid structures result in congested pores that inhibit active site cooperativity and the diffusivity of reagents, thus resulting in lower rates during the reaction.
本工作探索了二氧化硅/有机杂化催化剂的效能，其中有机组分由附着在载体介孔内二氧化硅载体上的线性氨基聚合物构建而成。具体而言，在4-硝基苯甲醛与丙酮的羟醛缩合反应中，研究了含胺原子转移自由基聚合合成的聚（苯乙烯-2-（4-乙烯基苄基）异吲哚啉-1,3-二酮）共聚物的分子量和聚合物链组成的作用。可控聚合产生了具有可控分子量和分散度的含保护胺的聚（苯乙烯）链，并且在催化反应之前，采用接枝到硫醇-烯偶联方法，随后进行邻苯二甲酰亚胺脱保护步骤，以共价连接并活化聚合物杂化催化剂。采用位点归一化间歇动力学来评估聚合物分子量和链组成在协同催化中的作用。结果表明，低分子量共聚物比仅由分子有机组分或高分子量链构建的催化剂更具活性。利用分子动力学模拟来探究聚合物柔韧性和形态的作用，由此确定较高分子量的杂化结构会导致孔道拥挤，从而抑制活性位点的协同作用和试剂的扩散率，进而导致反应速率降低。
