Synthesis of well-defined multigraft copolymers by a two-step living radical polymerization with nitroxyl-functionalized poly(methyl methacrylate)

Abstract

Novel multigraft copolymers of poly(methyl methacrylate-graft-polystyrene) (PMMA-g-PS) in which the number of graft PS side chains was varied were prepared by a subsequent two-step living radical copolymerization approach. A polymerizable 4-vinylbezenyl 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) monomer (STEMPO), which functioned as both a monomer and a radical trapper, was placed in a low-temperature atom transfer radical polymerization (60°C) process of methyl methacrylate with ethyl 2-bromopronionate (EPNBr) as an initiator to gain ethyl pronionate-capped prepolymers with TEMPO moieties, PMMA-STEMPOs. The number of TEMPO moieties grafted on the PMMA backbone could be designed by varying STEMPO/EPNBr, for example, the ratios of 1/2, 2/3, or 3/4 gained one, two, or three graft TEMPO moieties, respectively. The resulting prepolymers either as a macromolecular initiator or a trapper copolymerized with styrene in the control of stable free-radical polymerization at an elevated temperature (120 °C), producing the corresponding multigraft copolymers, PMMA-g-PSs. The nitroxyl-functionalized PMMA prepolymers produced a relatively high initiation efficiency (>0.8) as a result of the stereohindrance and slow diffusion of TEMPO moieties connected on the long PMMA backbone. The polymerization kinetics in two processes showed a living radical polymerization characteristic. The molecular structures of these prepolymers and graft copolymers were well characterized by combining Fourier transform infrared spectroscopy, gel permeation chromatography, chemical element analysis, and 1H NMR. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1876–1884, 2002