Porphyrin derivatives act as vinylene monomers in TEMPO-mediated radical copolymerization with styrene

In this article, we offer clear evidence for the radical copolymerizability of porphyrin rings in 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-mediated radical copolymerizations with styrene. The radical copolymerizations of styrene with 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (H2TFPP) was conducted using 1-phenyl-1-(2,2,6,6-tetramethyl-1-piperidinyloxy)ethane as an initiator. The refractive index (RI) traces for the size-exclusion chromatography of the resulting copolymers were unimodal with narrow molecular weight distributions. The RI traces shifted toward higher molecular weight regions as the polymerization progressed, and the number-average molecular weights were close to those calculated on the basis of the feed compositions and monomer conversions. These features were in good agreement with a TEMPO-mediated mechanism. The traces recorded by the ultraviolet-visible (UV-vis) detector (430 nm) were identical to those obtained by the RI detector, indicating a statistical copolymerization of styrene with H2TFPP. This also indicated that H2TFPP acted as a monomer and not as a terminator or a chain-transfer agent under the conditions used. A benzyl radical addition to H2TFPP was conducted as a model reaction for the copolymerization using tributyltin hydride as a chain-transfer agent, affording a reduced porphyrin, 2-benzyl-5,10,15,20-tetrakis(pentafluorophenyl)chlorin 1, via radical addition to the beta-pyrrole position. The UV-vis spectrum of 1 was fairly similar to that of poly(styrene-co-H2TFPP), indicating that H2TFPP polymerized at its beta-pyrrole position in the TEMPO-mediated radical polymerization. TEMPO-mediated radical copolymerizations of styrene with several porphyrin derivatives were also demonstrated. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012