Formation efficiency of ABA blockcopolymers via enhanced spin capturing polymerization (ESCP): Locating the alkoxyamine function

Enhanced spin capturing polymerization (ESCP) constitutes a versatile method for controlling the molecular weights during free radical macromolecular growth. The methodology employs nitrones as controlling agents, which are incorporated as alkoxyamines into the macromolecules in a midchain position (Ri-NO-Rj). It is demonstrated;via both simulations and experiments;that if the radical initiator and the nitrone are judiciously chosen, midchain functionalizations of over 90% can be achieved. Macromolecules with a nitroxide position in the midchain position can be employed in subsequent nitroxide mediated polymerizations to prepare ABA-type block copolymers. It is demonstrated that high yields of midchain macroalkoxyamine are generated as long as the employed nitrone displays low primary radical addition (governed by the addition rate coefficient k ad) in combination with a relatively rapid chain growth initiation rate (characterized by the primary radical initiation rate coefficient, k i). The absolute value of kad appears to be unproblematic for the success of Ri-NO-Rj formation by ESCP. In addition, it is of relatively high importance to employ a large nitrone concentration to achieve high degrees of Ri-NO-R j. The structure of ESCP prepared polystyrenes was confirmed (among other approaches) via thermally cleaving the Ri-NO-R j species and a subsequent quenching of the reaction to obtain a high yield of the individual arm species of half the length of the macroalkoxyamine. © 2009 American Chemical Society.