Xanthate-mediated controlled radical polymerization of N-Vinylindole derivatives

The polymerization of three N-vinylindole derivatives, N-vinylindole (NVIn), 2-methyl-N-vinylindole (2MNVIn), and 3-methyl-N-vinylindole (3MNVIn), were carried out by reversible addition-fragmentation chain transfer (RAFT)/macromolecular design via interchange of xanthate (MADIX) process. Five chain transfer agents (CTAs), S-benzyl-O-ethyldithiocarbonate (CTA 1), O-ethyl-S-(1-phenylethyl)dithiocarbonate (CTA 2), O-ethyl-S-[(2-cyano)prop-2-yl]dithiocarbonate (CTA 3), benzyl 1-pyrrolecarbodithioate (CTA 4), and benzyl dithiobenzoate (CTA 5), were compared for these polymerizations with 2,2'-azobis(isobutyronitrile) as an initiator. The xanthate-type RAFT agent (CTA 2) is the most efficient for obtaining poly(2MNVIn) with controlled molecular weights (M-n = 1700-19 400) and narrow molecular weight distributions (M-w/M-n = 1.20-1.40). The effects of several parameters, such as solvent, temperature, monomer concentration, and CTA-to-initiator molar ratio, were examined in order to determine the conditions leading to optimal control of the polymerization. The resulting polymers gave clear spectroscopic evidence of the formation of charge-transfer complexes with efficient sensitizers, such as 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), for photoconductivity. The poly(2MNVIn)s obtained by RAFT polymerization showed molecular weight dependence on the glass transition temperature (T-g = 150-190 degrees C) and thermal stability (T-d(10) = 300-430 degrees C).