Efficient Low-Temperature Atom Transfer Radical Coupling and Its Application to Synthesis of Well-Defined Symmetrical Polybenzamides

Radical coupling reactions have been widely used for preparation of symmetrical macromolecules. In previous studies of atom transfer radical coupling (ATRC), coupling efficiency above 90% has been generally attained at high temperature (T = 70–110 °C) by using Mn < 5000 precursors. From the mechanistic viewpoint, we designed a strategy for styrene-assisted ATRC from methacrylic macroradicals at low temperature (St/PMMA–Br/CuIBr/Cu0/Me6TREN). Analysis of the products (1H NMR, H–H COSY, MALDI–TOF mass spectra and gel permeation chromatography) indicated that this provides an efficient “convergent” or coupling approach, if a high degree of chain-end functionality is preserved. We then applied this concept in combination with chain-growth condensation polymerization (CGCP), which usually affords quantitative chain-end functionality. Couplings of high-molecular-weight AB-type diblock polybenzamide, 2-bromoisobutyryl-terminated poly(N-octyloxybenzyl-m-benzamide)-block-poly(N-octyl-m-benzamide) (Mn = 9300, Mw/Mn...