Synthesis of end- and mid-phthalic anhydride functional polymers by atom transfer radical polymerization

Polystyrene (PS) and poly(methyl methacrylate) (PMMA) having a single di-te rt-butyl phthalate (DTBP) group either at the chain end or in the middle of the chain were synthesized by Cu(I) ion mediated atom transfer radical pol ymerization (ATRP). The di-tert-butyl phthalate initiators 7 and 8 (for end -functional polymers) and 11 (for mid-functional polymers) were prepared fr om commercially available di-tert-butyl acetylene dicarboxylate (1) and myr cene (2) in four and six steps, respectively, with high overall yields. The DTBP functionalized polymers could be cleanly converted to the correspondi ng phthalic anhydride (PA) functional polymers by pyrolysis. The pyrolysis process could be easily monitored using conventional H-1 NMR spectroscopy, by observing the significant chemical shift change of the alkyl linker exis ting in the initiators. Kinetic study of the pyrolysis revealed that the me chanism of the DTBP group pyrolysis to phthalic anhydride (PA) group follow s two first-order consecutive reactions having a phthalic diacid (DA) as an observable intermediate. When the PA-functionalized PMMA was subjected to reactive blending at 180 degreesC with an amine-functionalized PS, the conv ersion reached a maximum (> 90%) in less than 2 min, which is considerably faster than the corresponding reaction of an aliphatic anhydride (e.g., suc cinic anhydride)-functionalized PMMA. A competition experiment with small m olecules showed that phthalic anhydride reacts similar to5 times faster tha n succinic anhydride with PS-NH2.