1 The Danish Polymer Centre, Department of Chemical and Biochemical Engineering, Technical University of Denmark2 Department of Chemical and Biochemical Engineering, Technical University of Denmark3 Department of Energy Conversion and Storage, Technical University of Denmark4 Polish Academy of Sciences
Multifunctional initiators for atom transfer radical polymerization (ATRP) are prepared by converting ditrimethylolpropane with four hydroxyl groups, dipentaerythritol with six hydroxyl groups, and poly(3-ethyl-3-hydroxymethyl-oxetane) with similar to 11 hydroxyl groups to the corresponding 2-bromoisobutyrates or 2-bromopropionates as obtained by reaction with acid bromides. Star polystyrene (PS) is produced by using these macroinitiators and neat styrene in a controlled manner by ATRP at 110 degrees C, employing the catalytic system CuBr and bipyridine. M. up to 51,000 associated with narrow molecular weight distributions (PDI <1.1) are obtained with conversions up to 32%. Hydrolysis of the star-PS leads to linear chains having the expected M-n values. The star-PS polymers based on dipentaerythritol degrade thermally in nitrogen in a two-step process in which the first low-temperature step involves scission of the ester linkages and the second step corresponds to the normal PS degradation. Star poly(methyl acrylates) with various cores are likewise prepared in a controlled manner by ATRP of methyl acrylate in bulk and in solution at 6080 degrees C with the 1,1,4,7,7-pentamethyldiethylene triamine ligand. Under these conditions, higher conversions were possible still maintaining low PDI signaling controlled star growth. Multiarm stars of poly(n-butyl acrylate) and poly(n-hexyl acrylate) with controlled characteristics have also been prepared.
Journal of Polymer Science. Part A, Polymer Chemistry, 2005, Vol 43, Issue 17, p. 3748-3759