An improved mimetic compound for styrene "living" free radical polymerization. An initiator containing the "penultimate" unit

A new thermal initiator for living free radical polymerization (LFRP) has b een synthesized photochemically by coupling of the free radical TEMPO with the 1,3-aiphenyl-1-propyl radical. This initiator (4), which contains the p enultimate monomer unit, is a much better mimetic compound than similar com pounds derived from radicals with a single styrene moiety, such as the 2-ph enylethyl radical (which yields adduct 2). In particular, 4 does not yield any disproportionation products, while other model compounds usually do. Th is is attributed to the lowest energy conformation of 4, which places the b eta-hydrogen atoms in an unfavorable stereoelectronic arrangement to give d isproportionation products. It is anticipated that the same situation will prevail in the polymer, and it is instrumental in determining the low polyd ispersities 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 wi th that of 2.