Corn starch-based graft copolymers prepared via ATRP at the molecular level

Ionic liquid was employed as a reaction medium to prepare starch-based macro-initiator for atom transfer radical polymerization (ATRP), due to its high dissolubility for starch and chemical inertness. Starch macro-initiators with varying degrees of substitution (DS) were successfully synthesized in ionic liquid 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) by homogeneous esterification with 2-bromoisobutyryl bromide at room temperature without the use of any additional catalysts. Starch-based copolymers (Starch-g-PS and Starch-g-PMMA) were prepared at the molecular level via homogeneous ATRP using CuBr/PMDETA and CuBr/BPY as catalysts. Compared with heterogeneous surface-initiated polymerization, the graft density and graft ratio were significantly improved. The structure and thermo behaviour of the graft copolymers were characterized by 1H NMR, FTIR and TGA. The molecular weights of the grafted polymer chains were analyzed by gel permeation chromatography (GPC) after hydrolyzing of the starch backbone from the copolymer. The effects of molar ratio of monomer to initiator, solvent, ligand and temperature on the graft polymerization were investigated as well.