Synthesis of Oxazoline-Terminated Polystyrene via Controlled-Radical Polymerization

Two novel bis(1,3-oxazoline-2-yl)-functionalized azo initiators were prepared, and their half-lives were determined by UV spectroscopy. These initiators were used in conjunction with 2,2,6,6-tetramethylpiperidin-1-yloxy (TEMPO) to afford controlled-radical styrene polymerization. Polymerization kinetics, molar mass versus conversion dependence and polydispersities with varying [TEMPO]/[initiator] ratios were examined, and the degree of endgroup functionalities was determined by NMR, FT-IR, endgroup titration and size exclusion chromatography (SEC) data. Well-defined narrow-distributed mono(1,3-oxazolin-2-yl)-terminated polystyrenes with molar mass varying between 1000 and 50 000 with polydispersities of 1.2−1.3 were obtained. The reactivity of the oxazoline moiety was proven by reacting monooxazoline-terminated polystyrene with monocarboxy-terminated polystyrene. Increases in molar mass and the formation of ester amide coupling groups, resulting from the reaction of oxazoline with carboxylic acid endgroups of polystyrene were monitored by means of SEC and FT-IR. Oxazoline endgroup conversion increased with decreasing polystyrene molar mass. Kinetics of the ester amide formation showed Arrhenius-type behavior. The activation energy of melt-phase ester amide formation was determined to be 65 kJ/mol.