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

Novel multigraft copolymers of poly(methyl methaerylate-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 (60degreesC) 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 degreesC), 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 H-1 NMR. (C) 2002 Wiley Periodicals, Inc