A facile synthesis of clickable and acid-cleavable PEO for acid-degradable block copolymers
End-functionalized polyethylene oxides containing cleavable acetal and clickable azide terminal groups (PEO-acetal-N3 and N3-acetal-PEO-acetal-N3) were obtained by the reaction between commercially available PEOs and 2-chloroethyl vinyl ether using pyridinium p-toluenesulfonate. This results in acetal-linkages which can be further functionalized by nucleophilic displacement with sodium azide. Both reactions proceeded quantitatively to produce clickable and cleavable PEOs in good yields. The obtained PEOs were subsequently converted into macroinitiators for nitroxide-mediated polymerization (NMP) by “click” reaction with an alkyne functionalized alkoxyamine. Styrene polymerization from the macroinitiators proceeded successfully to give well-defined acid degradable block copolymers (PEO-acetal-PS and PS-acetal-PEO-acetal-PS), all of which were shown to have narrow molecular weight distributions (Mw/Mn 1.2). Significantly, highly ordered nanophase separated thin films of hexagonally-packed cylindrical PEO domains embedded in a PS matrix could be prepared from the PEO-acetal-PS diblock copolymers with removal of the PEO block by treatment with acid yielding nanoporous thin films with primary hydroxyl groups decorating the pores' interiors.