Blocking Group/Initiators for the Synthesis of Polyrotaxanes <i>via</i> Free Radical Polymerizations

Abstract

Two new blocking group/initiators (BG/inits) were prepared. 4,4‘-Azobis[4-cyanopentanoic acid] (7) was converted to 4,4‘-azobis[4-cyanopentanoyl chloride] (8). The acid chloride 8 reacted with 4,4-bis(p-tert-butylphenyl)-4-phenylbutanol (5) to give 4,4-bis(p-tert-butylphenyl)-4-phenylbutyl 4,4‘-azobis[4-cyanopentanoate] (9, BG/init I) in quantitative yield. 4-[Tris(p-tert-butylphenyl)methyl]phenyl 4,4‘-azobis[4-cyanopentanoate] (10, BG/init II) was synthesized by room temperature esterification of 4,4‘-azobis[4-cyanopentanoic acid] (7) with tris(p-tert-butylphenyl)(4-hydroxyphenyl)methane (6) using the DCC coupling method. The results of the polymerization of styrene initiated by I and II indicated that both the BG/inits were well-behaved free radical initiators. Also, terminal group analysis by 1H NMR spectra showed that the blocking efficiencies for polystyrene were 100% due to the termination via radical coupling. These BG/inits can be used as free radical initiators and blocking groups at the same time in the synthesis of polyrotaxanes prepared by radical polymerizations.