No abstract

A four-pulse version of the pulsed double electron electron resonance (DEER) experiment has been applied to a series of TEMPO diradicals with well-defined interradical distances ranging from 1.4 to 2.8 nm (see picture). The new pulse sequence allows broad distributions of electron-electron distances to be measured without dead-time artifacts.

CuCI, TMEDA, 3,5-bis-(fert-butyi)phenylacetylene (0.01 eq.), 1 ,2-dichlorobenzene, molecular sieve 4,&, 02.65 'C, 3 h, 90 %

The homopolymerization of methyl methacrylate (MMA) in the presence of 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO) is described and compared to the TEMPO-mediated polymerization of styrene. Furthermore, the formation of block copolymers between MMA and styrene from polystyrene chains with TEMPO fragments as end groups is examined. The degree ofblock formation is estimated by GPC analyses. ESRexperiments are performed on the polystyrene chains to study the scission behavior of the TEMPO fragments.

Conformations of end-labeled alkanes in a rigid polymer matrix were investigated using the pulsed double electron-electron resonance (DEER) method. To this end, dipolar spectra of a series of aliphatic dicarbonic acids with 8−20 methylene units and chain ends bifunctionalized with nitroxide radicals were recorded in a polystyrene matrix. The biradicals are derived from hindered amine light stabilizers (HALS), used as polymer additives. Analysis of the dipolar spectra allows the determination of the end-to-end distances of the oligomer biradicals. The experiments show that the “flexible” alkane chains are almost completely stretched. This observation is consistent with the results of force field calculations.