Blocking-cyclization technique for precise synthesis of cyclic polymers with regulated topology

Jie Chen,Lidong Zhang,Meiran Xie,Hengchen Zhang,Huijing Han,Ruyi Sun,Xiaojuan Liao,Hongfei Li

doi:10.1038/s41467-018-07754-1

Abstract

Ring-closure and ring-expansion techniques are the two routes for extensive synthesis of cyclic polymers. Here, we report an alternative blocking-cyclization technique referred to as the third route to prepare cyclic polymers with regulated ring size and ring number by ring-opening metathesis polymerization of di- and monofunctional monomers in a one-pot process, where the polymer intermediates bearing two single-stranded blocks are efficiently cyclized by the cyclizing unit of propagated ladderphane to generate corresponding mono-, bis-, and tricyclic polymers, and the well-defined ladderphane structure plays a crucial role in forming the cyclic topology. Monocyclic polymer is further modified via Alder-ene reaction and the cyclic molecular topology is clearly demonstrated. The diversity features of cyclic polymers are comprehensively revealed. This strategy has broken through the limitations of previous two cyclizing routes, and indeed opens a facile and popular way to various cyclic polymers by commercial Grubbs catalyst and conventional metathesis polymerization.

Highlights

Ring-closure and ring-expansion techniques are the two routes for extensive synthesis of cyclic polymers
As a class of double-stranded polymers, ladderphane structure[27,28,29,30], constituted of multiple layers of rigid linkers connected to two polymeric backbones, has two independent propagating carbene ends in ring-opening metathesis polymerization (ROMP) process, which can further initiate the monofunctional monomers to form the AB2-type block copolymer, where ladderphane block A is a double-stranded segment and block B is a single-stranded segment[31,32,33]
It is astonishing to find that this technique possessed a versatility for preparing monocyclic c-[PBNP-(b-PTNP)2-b-PBNP] and multicyclic c-[PBNP-((b-PTNP)2-b-PBNP)x] polymers by the thirdgeneration Grubbs catalyst (Ru-III)-mediated successive ROMP of di- and monofunctional norbornene (NBE) derivatives, bis (BNP) containing the rigid perylene bisimide (PBI) linker and N-3,5-bisbiphenyl-norbornene pyrrolidine (TNP), as depicted in Fig. 2 and Supplementary Fig. 1

Summary

Introduction

Ring-closure and ring-expansion techniques are the two routes for extensive synthesis of cyclic polymers. The linear polymer precursor and highly diluted reaction condition are inevitably required in ring-closure technique, and the cyclization always occurs on the two reactive end groups of isolated polymer precursor without living species and must be triggered by the extra initiator. Another synthetic route is ring-expansion technique (Fig. 1b), and the in situ cyclization invariably arises from the cyclic living species, in which two types of cyclic catalysts play a crucial role. Because polynorbornene (PNBE) chain with N-arylpyrrolidine pendants adopted a rigid rod-like structure[34,35], the two B blocks attracted by the π–π stacking effect of pendants, resulting in that the two end groups of B blocks are in close proximity to each other

Methods

Results

Conclusion