Networked Polyphthalaldehydes Linked with Oxime Ether and Urethane Units and Their Photo-induced Depolymerization

Abstract

Photo-induced depolymerization is a useful technique in designing functional materials and polymer recycling. Polyphthalaldehyde (PPA) has been known to be depolymerizable even in solid state. In this study, networked PPAs linked with oxime ether and urethane units have been prepared, and their photo-induced depolymerization was attempted. The networked structure of PPAs was prepared by anionic polymerization of phthalaldehyde monomer (o-PA) initiated with trifunctional oxime and 1,8-diazabicyclo[5.4.0]undec-7-ene to form truxene core bearing three PPA chains, followed by termination with difunctional isocyanates. We could obtain networked PPAs from 1,5-naphthalene diisocyanate, although could not from hexamethylene diisocyanate. Obtained networked polymers were pressed in neat pellets and UV-irradiated with Hg-Xe lamp (>310 nm). By repeated irradiation in solid state and dispersed state in chloroform, almost of the PPAs became soluble in chloroform. In 1 H NMR spectra of the soluble fractions, peaks due to o-PA and phthalide were observed, suggesting the proceeding of almost complete decrosslinking and depolymerization. Trace amount of insoluble powder finally remained and discussed based on its IR spectrum. We also compared the scanning microscope images of PPAs before and after irradiation.