Synthesis and characterization of low-molecular-weight azo-acetoxystyrene and azo-naphthalene oligomers via stable free radical polymerization (SFRP)

As an approach toward controlled molecular architecture through stable free radical polymerization (SFRP), we have prepared a series of oligomers of controlled molecular weights (Mn) and low polydispersities (structures 2 and 3, with n values ranging from 2 to 52). Definitive evidence of structure was obtained through MALDI/MS (inter-peak interval of 162 m/z in azo-acetoxystyrene oligomers 2 and 260 m/z in azo-naphthalene oligomers 3, which correspond to the acetoxystyrene (AS) and naphthalenic (Np) repeating units, with corroborative evidence from NMR and GPC. Two synthetic pathways were explored. Pathway 1 yields azo-acetoxystyrene oligomer 2 via SFR addition of a TEMPO-capped unimer 1 to acetoxystyrene. Subsequent reactions would convert 2 into 3. In an alternative pathway 2, SFR addition of 1 to 4-(1-methoxynaphthyl)styrene gives azo-naphthalene oligomer 3 directly. Thus, the present reported methodology for controlled architecture has achieved synthesis of oligomers from low Mn (chlorobenzene, PhCl, solvent) to relatively high Mn (bulk), with incorporation of naphthyl (donor) and azobenzene (acceptor) moieties, as well as spacer moieties, in a controlled manner.