A convergent approach to ring polymers with narrow molecular weight distributions through post dilution in ring expansion cationic polymerization
A convergent approach to ring polymers with narrow molecular weight distributions through post dilution in ring expansion cationic polymerization
复制标题
通过扩环阳离子聚合中的后稀释制备具有窄分子量分布的环状聚合物的收敛方法
DOI：
10.1039/c6py01683a
复制
发表时间：
2016
影响因子：
4.6
通讯作者：
and Mitsuo Sawamoto
中科院分区：
文献类型：
--
作者：
Hajime Kammiyada;Makoto Ouchi;and Mitsuo Sawamoto
在本文中，我们展示了一种收敛的方法，将通过乙烯基醚与半缩醛酯（HAE）为基础的环引发剂（1）的扩环阳离子聚合得到的“稠”环链转化为窄分子量分布的“单”环链。在环膨胀增长过程中，可以控制增长而没有任何副反应，但是增长的环聚合物之间的HAE键之间的分子间抗衡阴离子交换反应不可避免地发生，导致由具有多个HAE键的“稠合”环链以及具有一个HAE键的“单”环链组成的宽分子量分布（MWD）。因此，在单体转化率达到超过95%之后，将聚合溶液稀释（即，后稀释）而不使所用的刘易斯酸活化剂失活（即，SnBr 4）诱导稠环链中的分子内抗衡阴离子交换。产物的尺寸排阻色谱（SEC）曲线最终变得几乎单峰，尽管来自稠合环的小肩峰仍然存在。重要的是，环链中的HAE键即使在后稀释过程后仍然存在，这通过1H NMR证实，并且环结构的保留也得到酸解实验的支持，其中SEC中的表观峰顶分子量（Mp）由于从环状到线性的拓扑结构转化而增加。该方法被证明是有效的，即使是较高的分子量的环聚合物，制备具有较高的[单体]/[1]的比例，以及环嵌段共聚物。
In this paper, we demonstrate a convergent approach to convert “fused” ring chains obtained via ring expansion cationic polymerization of vinyl ether with a hemiacetal ester (HAE)-based ring initiator (1) into “sing” ring ones of narrow MWDs. In the ring-expansion propagation process, the propagation can be controlled without any side reactions but an intermolecular counteranion exchange reaction between HAE bonds between propagating ring polymers ineluctably occurs resulting in broad molecular weight distributions (MWDs) composed of “fused” ring chains with multiple HAE bonds as well as a “sing” ring chain with one HAE bond. Hence, after monomer conversion reached over 95%, the polymerization solution was diluted (i.e., post dilution) without deactivation of an employed Lewis acid activator (i.e., SnBr4) to induce intramolecular counteranion exchange in the fused ring chain. Size exclusion chromatography (SEC) curves of the product eventually became almost unimodal, though a small shoulder peak from the fused ring remained. Importantly, the HAE bond in ring chains still survived even after the post dilution process, which was confirmed by 1H NMR, and the retention of the ring structure was also supported by an acidolysis experiment where the apparent peak top molecular weight (Mp) was increased in SEC due to topology conversion from a ring to linear. The approach was proved to be effective even for higher molecular weight ring polymers that were prepared with a higher [monomer]/[1] ratio as well as ring block copolymers.