Linear and Hyperbranched Glycopolymer-Functionalized Carbon Nanotubes: Synthesis, Kinetics, and Characterization

Abstract

Linear and hyperbranched glycopolymers, a kind of sugar-containing polymers, were grown successfully from surfaces of multiwalled carbon nanotubes (MWNTs) by the “grafting from” strategy with good controllability and high reproducibility. Linear glycopolymer was grafted from the surfaces of MWNTs by surface-initiated atom transfer radical polymerization (ATRP) of 3-O-methacryloyl-1,2:5,6-di-O-isopropylidene-d-glucofuranose (MAIG) with CuIBr/HMTETA (1,1,4,7,10,10-hexamethyltriethylenetetramine) at 60 °C in ethyl acetate. After hydrolysis of polyMAIG in 80 wt % formic acid for 48 h, water-soluble poly(3-O-methacryloyl-α,β-d-glucopyranose) (polyMAG)-grafted MWNTs were obtained. The kinetics were investigated by carrying out the polymerizations using 2-bromo-2-methylpropionyl-immobilized MWNTs (MWNT−Br) as the macroinitiator in the absence or presence of ethyl 2-bromoisobutyrate as sacrificial initiator. In both cases a linear dependence of molecular weight on conversion was obtained, and the polymer amounts grafted on MWNTs could be well controlled in a wide range by the reaction time and monomer conversion. Coupling was found in the GPC curves of free polymer when the conversion of monomer reached ca. 45−50%. This clearly indicates that coupling reactions are more predominant than the conventional ATRP in a homogeneous solution without CNTs, where no coupling occurred despite of very high conversion of this monomer (>80%). Hyperbranched glycopolymers (HPGs) were also grafted from the surfaces of MWNTs by self-condensing vinyl copolymerization (SCVCP) of the monomer, MAIG, and inimer, 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEMA, AB*) via ATRP with bis(triphenylphosphine)nickel(II) bromide ((PPh3)2NiBr2) at 100 °C in ethyl acetate. After deprotection in formic acid, hyperbranched glycopolymers with high density of hydroxyl groups functionalized MWNTs were achieved. The novel water-soluble biocompatible glycopolymer-grafted CNTs have fascinating potentials in the fields of tissue engineering and bionanomaterials.