HOMOPOLYMERIZATIONS OF METHYL-METHACRYLATE AND STYRENE - CHAIN TRANSFER CONSTANTS FROM THE MAYO EQUATION AND NUMBER DISTRIBUTIONS FOR CATALYTIC CHAIN TRANSFER, AND THE CHAIN-LENGTH DEPENDENCE OF THE AVERAGE TERMINATION RATE COEFFICIENT

The catalytic chain transfer agent [bis[mu-[(2,3-butanedione dioximato )(2-)-O,O']] tetrafluorodiborato(2-)-N,N',N '' N''']cobalt (COBF) was investigated in polymerizations of methyl methacrylate and styrene in bulk and in methyl methacrylate in toluene solution. A wide range of p olymer molecular weights were produced by these reactions under identi cal polymerization conditions, enabling the use of these reactions in the examination of the chain length dependence of the average terminat ion rate coefficient. A strong chain length dependence in accord with theoretical predictions for diffusion-controlled termination was obser ved. A total of five variations of the use of the Mayo equation and th e shape of the number distribution were compared as methods of evaluat ing the chain transfer activity of COBF. MALDI-TOF mass spectrometry a nd SEC were evaluated for measuring the number distributions of the po lymers and deficiencies were exhibited in the distributions from MALDI -TOF. Both the number distribution and Mayo treatments of the data gav e similar results. COBF was shown to have a very high chain transfer a ctivity in all of these polymerizations. Chain transfer activities of ca. 36000 were found for COBF in bulk MMA, ca. 25000 for MMA in toluen e solution, and ca. 1500 for bulk styrene. A marked solvent effect is shown for toluene in the COBF-mediated polymerization of MMA.