Complex Macromolecular Architectures by Atom Transfer Radical Polymerization

Abstract: Controlled radical polymerization has proven to be a viableroute to obtain polymers with narrow polydispersities (PDI's)and controlled molecular weights under simple reactionconditions. It also offers control over the chain-]ends of thesynthesized polymer. Atom transfer radical polymerization(ATRP) is the most studied and utilized of these techniques. Inthis study ATRP has been utilized as a tool to obtain differentcomplex macromolecular structures.In order to elaborate a system for which a multitude ofchains can polymerize in a controlled manner and in closeproximity to one another, a multifunctional initiator based onpoly(3-ethyl-3-(hydroxymethyl)oxetane was synthesized. Themacroinitiator was used to initiate ATRP of methyl acrylate(MA). The resulting dendritic-]linear copolymer hybrids hadcontrolled molecular weights and low PDI's. Essentially thesame system was used for the grafting of MA from a solidsubstrate, cellulose. A filter paper was used as cellulosesubstrate and the hydroxyl groups on the cellulose weremodified into bromo-]ester groups, known to initiate ATRP.Subsequent grafting of MA by ATRP on the cellulose made thesurface hydrophobic. The amount of polymer that was attached tothe cellulose could be tailored. In order to control that thesurface polymerization was -eliving-f and hence that thechain-]end functionality was intact, a second layer of ahydrophilic monomer, 2-hydroxyethyl methacrylate, was graftedonto the PMA- grafted cellulose. This dramatically changed thehydrophilicity of the cellulose.Dendronized polymers of generation one, two and three weresynthesized by ATRP of acrylic macromonomers based on2,2-bis(hydroxymethyl)propionic acid. In the macromonomerroute, macromonomers of each generation were polymerized byATRP. The polymerizations resulted in polymers with low PDI's.The kinetics of the reactions were investigated, and thepolymerizations followed first-order kinetics when ethyl2-bromopropionate was used as the initiator. In the-egraft-]onto-f route dendrons were divergently attached to adendronized polymer of generation one, that had been obtainedby ATRP.