Reversible Switching between Linear and Ring Polystyrenes Bearing Porphyrin End Groups

摘要

A route to macrocyclic polymers based on a new unimolecular ring-closure process has been investigated. It involves the direct end-to-end coupling of an a, ω-bis[chloroiron(Ⅲ) meso-tetraphenylporphyrin] teleche-lic linear polystyrene synthesized by living polymerization followed by chain-end functionalization. The corresponding macrocyclic polystyrene was obtained readily and selectively by intramolecular condensation of the α,ω-bis-[chloroiron(Ⅲ) meso-tetraphenylporphyrin] polymer ends in the presence of a base to yield a diiron(Ⅲ)-μ-oxobis-(porphyrin) dimer as ring-closing unit. Addition of dilute HC1 was shown to rapidly reconvert the diiron(Ⅲ)-μ-oxobis(porphyrin) unit into the initial bis[chloroiron(Ⅲ) porphyrin], demonstrating the selectivity and complete reversibility of the cyclization process. The synthesis and detailed structural characterization of the α,ω-homodi-functional precursor and the corresponding macrocyclic polystyrene along with an analysis of the porphyrin dimer-ization reaction using NMR spectroscopy and size-exclusion chromatography coupled with a diode array detector are presented.