The synthesis of linear polymers with both ends conserved is severely impeded due to the inevitable macrocyclization in step-growth polymerization (SGP). Indeed, macrocyclic polymers are considered as the ultimate destination of polycondensations for AB or A₂ + B₂ monomer combinations. Here, we present a new strategy to limit the macrocyclization process towards the selective formation of linear polyesters in the polycondensations of ω-hydroxyaliphatic acid and the combinations of dicarboxylic acids and diols. By embedding the catalyst (sulfonic acid) in dendritic mesoporous silica nanoparticles (DMSNs), the polyesterifications were ushered to exclusively take place in the confined nanopores of DMSNs. The distribution of the α,ω-ends in different positions in the bundle of polyesters limited the end-to-end cyclization, leading to the selective chain extension especially in the high molecular weight region. NMR, GPC and MALDI-TOF results show that while the polyesters obtained in homogeneous polycondensation or with a nonporous heterogeneous catalyst were mainly with cyclic structures, the selective formation of linear polyesters was found in the confined nanopores of DMSNs. This finding contradicts the general sense that confined geometries are in favor of macrocyclization and provides a new understanding to manipulate the polymerization process towards the control of cyclic and linear topologies.

中文翻译：

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受限纳米孔中的缩聚对窄分散线型聚酯的选择性形成

由于逐步增长聚合（SGP）中不可避免的大环化，严重阻碍了两端保守的线性聚合物的合成。事实上，大环聚合物被认为是 AB 或 A ₂ + B _{2缩聚的最终目的地}单体组合。在这里，我们提出了一种新的策略来限制大环化过程，以在 ω-羟基脂肪酸缩聚以及二羧酸和二醇的组合中选择性地形成线性聚酯。通过将催化剂（磺酸）嵌入树枝状介孔二氧化硅纳米粒子（DMSNs）中，聚酯化反应只发生在 DMSNs 的受限纳米孔中。α，ω-末端在聚酯束中不同位置的分布限制了端对端环化，导致选择性扩链，尤其是在高分子量区域。NMR、GPC和MALDI-TOF结果表明，均相缩聚或使用无孔非均相催化剂获得的聚酯主要具有环状结构，在 DMSN 的受限纳米孔中发现了线性聚酯的选择性形成。这一发现与受限几何结构有利于大环化的普遍认识相矛盾，并为操纵聚合过程以控制循环和线性拓扑结构提供了新的理解。