Living cationic polymerization of 4-tert-butoxystyrene and synthesis of poly(4-vinylphenol) with narrow molecular weight distribution

Cationic polymerization of 4-tert-butoxystyrene (1) initiated by hydrogen iodide/zinc iodide (HI/ZnI2) led to well-defined living polymers at temperatures up to +25°C in either toluene or methylene chloride, the latter containing a small amount of tetrabutylammonium iodide (mole ratio nBu4NI/HI = 1/100). The number-average molecular weight of the polymers increased in direct proportion to the monomer conversion, and the linear increase further continued upon addition of a second feed of 1 to the completely polymerized reaction mixture. Both before and after the monomer addition, the molecular weight distributions of the products were invariably very narrow (M̄w/M̄n ≤ 1,1). In the polymerization in salt-free methylene chloride, in contrast, the polymers showed broader molecular weight distributions, particularly at low conversions, and thus the presence of the ammonium salt proved mandatory for attaining living polymerization in this polar solvent. By treatment with hydrobromic acid the HI/ZnI2-initiated poly(1) could readily be converted into poly(4-vinylphenol) (3) that inherited the narrow molecular weight distribution and controlled molecular weight of the precursor.