Abstract
Series of binitroxides, (N,N′-bis(4-(2,2,6,6-tetramethylpiperidin-1-yloxyl)diaminoalkane), ·Cn· (n=0, 2, 3, 4 methylene groups), was used as mediators in the radical polymerization of styrene initiated with benzoyl peroxide (BPO). The length of the methylene spacer linking two 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radicals affected the polymerization process. For the mediators, ·C0·, ·C2· and ·C3·, elongation of the spacer decreases the conversion rate as well as the number average molecular weight (Mn), molecular weight distribution (MWD) and polydispersity index (PDI). For all these mediators, a bimodal MWD was confirmed. The use of N,N′-bis(4-(2,2,6,6-tetramethylpiperidin-1-yloxyl))diaminobutane, ·C4·, results in trimodal MWD with an additional polymer fraction with a high molecular weight originating from an uncontrolled process. In the initial stages of polymerization, electron spin resonance spectroscopy (ESR) showed that the combination reaction between ·C4· and growing polymer chain (P·) is much slower than that for the ·C0· controlling agent, thereby promoting the synthesis of long polymer chains. With the exception of the ·C0· mediator, the remaining biradicals did not exhibit spin-spin interactions between the TEMPO groups in the propagation of polymerization. Therefore, the spin-spin coupling between binitroxide ends does not appear to have a remarkable influence on the polymerization process. Open image in new window
Published Version
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