LIVING CATIONIC POLYMERIZATION OF P-METHOXYSTYRENE BY THE HI/ZNI2 AND HI/I2 INITIATING SYSTEMS - EFFECTS OF TETRABUTYLAMMONIUM HALIDES IN A POLAR-SOLVENT

The effects of added salts (nBu4NX; X = I, Br, Cl, ClO4) on the cationic polymerization of p-methoxystyrene (pMOS) by the hydrogen iodide/zinc iodide (HI/ZnI2) or hydrogen iodide/iodine (HI/ I2) initiating systems were investigated at -15 and +25 °C in methylene chloride (CH2C12) as a polar solvent. In salt-free CH2C12, the molecular weight distributions (MWDs) of the polymers were bimodal, where the higher molecular weight polymer peak was nonliving, whereas the lower molecular weight polymer fraction had a long lifetime. When a small amount of nBu4NI (1.0 mol % to HI) was added in the solvent, the higher polymer fraction was completely eliminated to give polymers with very narrow MWDs (Mw/Mn < 1.1) that turned out to be living (at -15 °C with HI/I2 and even at +25 °C with HI/ZnI2). The number average molecular weight (Mn) of the polymers increased in direct proportion to pMOS conversion, continued to increase upon sequential addition of pMOS feeds, and were in good agreement with the calculated values assuming one living chain per HI. Very similar living polymerizations occurred when nBu4NBr or nBu4NCl was employed in place of the iodide salt; however, the use of nBu4NC104 did not effect such a living process at all. It is concluded that through their high nucleophilicity, the added halide anions efficiently eliminate a dissociated nonliving growing species (1), thereby selectively permitting living propagation via the nondissociated living counterpart (2) (Scheme I). © 1990, American Chemical Society. All rights reserved.