Anthracene-maleimide-based Diels-Alder "click chemistry" as a novel route to graft copolymers

Using the Diels-Alder (DA) "click chemistry" strategy between anthracene and maleimide functional groups, two series of well-defined polystyrene-g-poly(ethylene glycol) (PS-g-PEG) and polystyrene-g-poly(methyl methacrylate) (PS-g-PMMA) copolymers were successfully prepared. The whole process was divided into two stages: (i) preparation of anthracene and maleimide functional polymers and (ii) the use of Diels-Alder reaction of these groups. First, random copolymers of styrene (S) and chloromethylstyrene (CMS) with various CMS contents were prepared by the nitroxide-mediated radical polymerization (NMP) process. Then, the choromethyl groups were converted to anthryl groups via the etherifaction with 9-anthracenemethanol. The other component of the click reaction, namely protected maleimide functional polymers, were prepared independently by the modification of commercially available poly(ethylene glycol) (PEG) and poly(methyl methacrylate) (PMMA) obtained by atom transfer radical polymerization (ATRP) using the corresponding functional initiator. Then, in the final stage PEG and PMMA prepolymers were deprotected by retro-Diels-Alder in situ reaction by heating at 110°C in toluene. The recovered maleimide groups and added anthryl functional polystyrene undergo Diels-Alder reaction to form the respective (PS-g-PEG) and (PS-g-PMMA) copolymers. The graft copolymers and the intermediates were characterized in detail by using ¹H NMR, GPC, UV, fluorescence, DSC, and AFM measurements.