An Improved Mimetic Compound for Styrene “Living” Free Radical Polymerization. An Initiator Containing the “Penultimate” Unit
journal contributionposted on 27.04.2000, 00:00 by W. G. Skene, J. C. Scaiano, Glenn P. A. Yap
A new thermal initiator for living free radical polymerization (LFRP) has been synthesized photochemically by coupling of the free radical TEMPO with the 1,3-diphenyl-1-propyl radical. This initiator (4), which contains the penultimate monomer unit, is a much better mimetic compound than similar compounds derived from radicals with a single styrene moiety, such as the 1-phenylethyl radical (which yields adduct 2). In particular, 4 does not yield any disproportionation products, while other model compounds usually do. This is attributed to the lowest energy conformation of 4, which places the β-hydrogen atoms in an unfavorable stereoelectronic arrangement to give disproportionation products. It is anticipated that the same situation will prevail in the polymer, and it is instrumental in determining the low polydispersities achievable with LFRP. This report includes a detailed study of the properties of 4, including its thermal decomposition and relevant free radical kinetics, as well as a comparison of the rotational barrier of 4 with that of 2.