Atom Transfer Radical Polymerization with Ti(III) Halides and Alkoxides

SummaryTi(III) compounds (halides and n-butoxide) along with several mono-, bi-, and tridentate ligands have been studied for the first time in the atom transfer radical polymerization (ATRP) of styrene. The important advantage of titanium compounds is the white color of the Ti(IV) ions (Ti in the highest and air stable oxidation state) which ensures the absence of coloring in the final polymer. The better control over polymerization was realized when conditions increasing the reactivity of the intermediate Ti(IV) species and decreasing their steady state concentration were maintained. This occurred when chlorides were replaced with bromides (which decreased the bond strength), and when ligands with low donor ability were employed. Using a sulfide complex of Ti(III) chloride and 1,2-bis(hexylthio)ethane allowed styrene polymerization with kinetic and molecular weight characteristics inherent to ATRP.