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 polystyrenegpoly(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 H-1 NMR, GPC, UV, fluorescence, DSC, and AFM measurements.