A photo-degradable helix: Synthesis, structure, and photolysis of optically active poly[2,7-bis(4-t -butylphenyl)-9-methylfluoren-9-yl acrylate

Abstract

2,7-Bis(4-t-butylphenyl)-9-methylfluoren-9-yl acrylate (BBPMFA) was synthesized and polymerized using α,α′-azobisisobutyronitrile or n-Bu3B-air as a radical initiator and using the complex of 9-fluorenyllithium with (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine as an optically active anionic initiator. Although the radical polymerization led to rather low-molecular-weight products at low yields, the anionic polymerization afforded polymers with higher molecular weights in higher yields. The poly(BBPMFA) obtained by the anionic polymerization was slightly rich in isotacticity (meso diad 57%) and showed an intense circular dichroism (CD) spectrum and large dextrorotation. The intensity of the CD spectrum and magnitude of optical activity increased with an increase in Mn, suggesting that the polymer possesses a preferred-handed helical conformation. The CD spectrum disappeared within 1 s on irradiation to the polymer in a CHCl3 solution using a 500-W Hg-Xe lamp. This was ascribed to fast photolysis of the ester linkage leading to a loss of helical conformation of the entire chain. Photolysis products of poly(BBPMFA) were poly(acrylic acid) and 2,7-bis(4-t-butylphenyl)-9-methylenefluorene (2,7-bis(4-t-butylphenyl)dibenzofulvene). The photolysis reaction seemed to proceed through the “unzipping” mechanism. The rate constant of photolysis of poly(BBPMFA) under irradiation at monochromated 325 nm was around 0.01 s−1 independent of molecular weight. Photolysis at 325 nm was approximately 2400 times faster than that for chemical ester solvolysis under a neutral condition in the dark. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011