Transition-metal-free controlled polymerization for poly(-aryleneethynylene)s.

A transition-metal-free controlled polymerization for the attainment of poly(-aryleneethynylene)s is developed. The polymerization of 1-pentafluorophenyl-4-[(trimethylsilyl)ethynyl]benzene with a catalytic amount of fluoride anions proceeds in a chain-growth-like manner to afford polymers with controlled molecular weights and low polydispersity indexes. The mechanism involves a pentacoordinated fluorosilicate as a key intermediate.

Accordion-like oscillation of contracted and stretched helices of polyacetylenes synchronized with the restricted rotation of side chains.

A chiral substituted acetylene, (s)-2-octyl propiolate, was stereoregularly polymerized using a catalyst, [Rh(nbd)Cl]2, at 40 °C in methanol to give the corresponding helical polymer, Ps2OcP. The changes of (1)H and (13)C NMR spectra in line shapes and splitting patterns were consistently interpreted in terms of restricted rotation around the ester O-*C bond, ~O-*C(ε)H(ε)(R)~, R = a branched CH(ε)3 in the ester side chains rather than the helix inversion with the aid of a 3-site jump model. Three peaks due to the branched methyl H(ε) proton and its C(η) carbon observed at 0 °C suggested the formation of three rotamers called A, B, and C, based on the presence of the contracted helix and stretched helix forms that have an intrinsic helical pitch.