Polystyrene with Designed Molecular Weight Distribution by Atom Transfer Radical Coupling

Abstract

Copper-mediated atom transfer radical coupling (ATRC) was studied for monobrominated and dibrominated polystyrenes as well as their mixtures. In the ATRC process macroradicals, generated in situ by an atom transfer radical equilibrium, participate in coupling reactions in the presence of a reducing agent, such as nanosize copper, zerovalent iron, tin octanoate (SnOct2), and ascorbic acid. 1H NMR analyses performed on the coupling product of monobrominated polystyrene (PStBr) showed the disappearance of the signal attributed to the methine proton located in the α-position to the bromine. ATRC is influenced by the nature of ligand as well as the amounts of ligand and zerovalent metal used in the process. The molecular weight of the coupling product is a function of the extent of coupling, which is defined by the proportion of polymeric chains participated in the reaction. Thus, molecular weights of the ATRC products of monobrominated polystyrene were approximately twice higher than those of PStBr precursors, while the polydispersities were low. The coupling of α,ω-dibrominated homologues gave high molecular weight products with higher polydispersities.