Rigid-to-Flexible Conformational Transformation: An Efficient Route to Ring-Opening of a Tröger’s Base-Containing Ladder Polymer

Abstract

The synthesis of ladder polymers is still a big challenge in polymer chemistry, and in particular, there are few examples of conformationally flexible well-defined ladder polymers. Here we report an efficient and convenient route to conformationally flexible ladder polymers, which is based on a postpolymerization reaction of a rigid ladder polymer containing Tröger’s base in its main chain. The postpolymerization reaction involves sequential N-methylation and hydrolysis for the Tröger’s base unit, resulting in a diazacyclooctane skeleton that can exhibit a ring-flipping motion. Molecular dynamics simulations predicted that this motion provides conformational flexibility with the resultant ladder polymer, which was demonstrated by 1H NMR spectroscopy in solution. The presence of the diazacyclooctane units in the flexible ladder polymer allowed further functionalization through reactions involving its secondary amine moiety. The present synthetic method may lead to the development of a new class of ladder polymers that exhibit both conformational and design flexibility.

Hydrophilic Microporous Polymer Membranes: Synthesis and Applications

“…The quaternary bicyclic ammonium groups have been proved to have poor stability due to ringopening side reaction under alkaline conditions (Figure 5a). [34,45] This reaction converts quaternized TB units to diazacyclooctane units, resulting in the loss of charged functional groups and the decrease in chain rigidity (Figure 5b). As a result, the resulting polymer is less porous in the solid state.…”

“…As a result, the resulting polymer is less porous in the solid state. [34] Yet from an alternative perspective, the ring-opening side reaction provides a convenient route to synthesizing new ladder polymers, i. e. diazacyclooctane-containing polymers, which contain hydrophilic secondary amine groups. Li, et al employed this method to modify PIM-DMBP-QTB, fabricating membranes with increased hydrophilicity for ultrafiltration.…”

“…[32] An AEMFC assembled with DMDPM-BP-QTB delivers a considerable maximum power density of 202 mW cm À 2 . [33] However, TB-based polymers may have poor chemical stability under harsh alkaline conditions ( Figure 5), [34,45] leading to a short lifetime. Thus, AEMs from microporous PIMs with chemically stable cationic functional groups are in great demand.…”

“…Noting that the chemical stability of quaternary bicyclic ammonium groups in PIM-QTB may be poor under harsh alkaline conditions. [34] Yamaguchi et al presented another strategy towards microporous polymer having trimethylammonium groups (Figure 2b, QA-PIM-1). The strategy exploited the halomethylation of benzylmethyl groups of PIM-1 and subsequent quaternization with trimethylamine.…”

Facile Access to Optically Active 2,6‐Dialkyl‐1,5‐Diazacyclooctanes

“…Moreover, the flexible conformation of the 8-membered ring makes 1,5-DACO, andi ts derivatives become versatile templates for novel material synthesis. [10] Despite its potential application,t he straightforwards ynthesis of chiral substituted 1,5-DACO remains challenging. An example of the synthesis of unsubstituted 1,5-DACOw as reported by Bçrjesson (Figure 1b).…”