화학공학소재연구정보센터
Journal of Polymer Science Part A: Polymer Chemistry, Vol.50, No.19, 4073-4084, 2012
A styryl tipno-based nitroxide as efficient mediator for the synthesis of multiblock polystyrenes and well-grafted polymers
The chloromagnesium exchange of 4-chlorostyrene provides an easy access to a new versatile polymerizable 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO)-based nitroxide. Indeed, first, its alkoxyamine based on the a-methyl benzyl radical fragment efficiently mediates the polymerization of styrene (respectively n-butyl acrylate) to yield branched polystyrene [respectively poly(n-butyl acrylate)] with alkoxyamine function as branch point and well-defined branches. Second, the self-condensing of this polymerizable nitroxide by manganese coupling affords a mixture of oligomeric linear polyalkoxyamines. Polymerization of styrene mediated with these polyalkoxyamines gives multiblock polystyrenes with alkoxyamine group as linker between polystyrene blocks and exhibits the following features: the synthesis of the polystyrene blocks is controlled as their average molecular weight Mn(block) increases linearly with conversion and their average dispersity Mw/Mn(block) decreases with it. At a given temperature, the molecular weight and the dispersity of the polyalkoxyamines weakly impact Mn(block) and Mw/Mn(block). In contrast, the molecular weight of the multiblock polystyrene increases linearly with conversion until reaching a constant value. The number of block is independent of the molecular weight of the polyalkoxyamines. These unusual results can be explained by the fact that during polymerization, mediating TIPNO-based polymeric nitroxides with different lengths are generated and are exchanged. Finally the dispersity of the multiblock polystyrene is quite broad and lies between 1.7 and 2.8. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012