POLYMERIZATION OF METHYL-METHACRYLATE WITH TERT-BUTYLLITHIUM AND TRIISOBUTYLALUMINUM IN TOLUENE - MECHANISM OF INITIATION AND TERMINATION BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY (MALDI TOF MS)

The polymerisation of methyl methacrylate (MMA) using triisobutylalumi nium/tert-butyllithium in hydrocarbon at 0 degrees C and -78 degrees C has been investigated by matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI TOF MS). Although the system g ives extremely good control over molecular weight and narrow molecular weight distribution, initiation of polymerization can be complicated by formation of small amounts of tert-butyl isoprenyl ketone (1), and termination of polymerization can occur by end cyclisation of the end unit of 3. Both complications in initiation and termination can be avo ided by suitable reaction conditions. Incorporation of 1 is suppressed by increasing the alkylaluminium content and by higher temperature. T ermination by cyclisation has been found to occur over much longer tim e scales than propagation and can therefore be avoided by controlled t ermination after the appropriate reaction time.