Tri‐armed star polymers by living cationic polymerization, 3. Synthesis of tri‐armed star poly(p‐methoxystyrene)

Tri‐armed star polymers of p‐methoxystyrene (pMOS) were synthesized by living cationic polymerization with a trifunctional initiator CH3C[(p‐)C6H4OCH2CH2OCH(CH3)I]3 (6) or C6H3(1,3,5‐)[COOCH2CH2OCH(CH3)I]3 (9) with zinc iodide as activator in toluene at −15°C. The number‐average molecular weight (Mn) of the polymers increased proportionally to the monomer conversion and further increased upon addition of fresh feed of pMOS to completely polymerized reaction mixtures; the polymers invariably exhibited very narrow molecular‐weight distributions (MWD) (Mw/Mn < 1,1). The living polymers were terminated with 2‐hydroxyethyl methacrylate to give a tri‐armed macromonomer where each arm is capped with a methacrylate group, and the quantitative end‐capping, in turn, showed the existence of three living ends per molecule. When the ester‐type initiator residue (core) of the poly(pMOS), obtained with the 9/ZnI2 system, was hydrolyzed under alkaline conditions, Mn was reduced to one third of the original value, with the narrow MWD being unchanged, thus indicating that the polymer possesses three arms with uniform and controlled length.