Formation Efficiency of ABA Blockcopolymers via Enhanced Spin Capturing Polymerization (ESCP): Locating the Alkoxyamine Function

Abstract

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 (R i -NO-R j ). 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 k ad appears to be unproblematic for the success of R i -NO-R j formation by ESCP. In addition, it is of relatively high importance to employ a large nitrone concentration to achieve high degrees of R i -NO-R j . The structure of ESCP prepared polystyrenes was confirmed (among other approaches) via thermally cleaving the R i -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.

Enhanced spin capturing polymerization: Numerical investigation of mechanism

“…In one of the first work on ESCP Junkers et al were looking for the location of nitroxyl moiety in polymer chain. They considered the detailed reaction scheme [Scheme , reactions (I)–(VI)] for ideal mechanism of the ESCP process.…”

“…To evaluate the influence of overestimation of C SC we compared the values of experimentally derived M n and conversion found in literature and the same parameters calculated with the values of C SC from literature and the ones after correction. For that purpose, we took the data published by Barner‐Kowollik et al Table summarized the results obtained. As one can see the estimation of M n and conversion using corrected value of C SC according to eq is very close to the experimental values.…”

“…The most attractive property of the ESCP process is that the resulting polymer represents macroalkoxyamine with nitroxyl moiety located statistically in the middle of polymeric chains. This fact allows one for easy preparing an ABA three block copolymer and other complex polymeric structures …”

“…Furthermore there are number of works on theoretical investigation of NMP kinetics . As for ESCP to the best of our knowledge there is only work of Junkers et al who used PREDICI simulation for investigation of the selected parameters influence on ESCP products. Comprehensive numerical analysis of ESCP kinetics has not been done yet.…”

Enhanced Spin Capturing Polymerization of Ethylene

“…Almost 90% of the chains were functionalized when 0.5 equiv of PBN was used (entry 5 in Table 1), which is close to the value obtained for polystyrene prepared by ESCP (95%). 4 Thus, polyethylene segments are located on both side of the alkoxyamine group, though the molecular weight of each block still has to be determined.…”