YLIDE MEDIATED POLYMERIZATION ACRYLATES IN THE PRESENCE OF OF METHACRYLATES AND TETRAPHENYLPHOSPHONIUM CATION-3

Triphenylmethide tetraphenylphosphonium (TPM,TPP) or methylisobutyrate tetraphenylphosphonium (MIB,TPP) formed by ion exchange reactions of TPP chloride(TPPCl) with the TPM or MIB potassium salts in THF, initia te the living polymerization of MMA producing PMMA's with narrow MW di stributions (below 1.3) at ambient temperatures. In the presence of sm all amounts (10 mole% or less) of water, that is often present in the TPPCl, this water, under the polymerization conditions, participates i n side reactions giving rise to the formation of triphenylphosphine ri nd of a potassium PMMA enolate that causes chain termination giving in complete MMA conversions and much wider PMMA distributions. The corres ponding polymerizations of acrylates can also produce relatively narro w MWD (<2.00) poly(n-butylacrylate)s and PMMA-b-polybutylacrylate bloc k copolymers but these acrylate polymerizations are not living on the polymerization time scale and can be demonstrated by NMR and other tec hniques to undergo Claisen type side reactions followed by highly effi cient proton, transfers from the formed cyclic (-keto esters to the ac tive acrylate chain end anions. Both UV/Visible spectroscopy of this m odel (maximum at 415 nm) and 1H, 13C and 31P NMR studies of the MIB,TP P model of the propagating PMMA chains show the presence of a 2,5-cycl ohexadienyl phosphor ylide formed by addition of the MIB enolate anion to the pam position of one of the four phenyls of the TPP. These and other data seem to be consistent with an equilibrium between the ylide and a small fraction of the MIB,TPP ion pair that may be partially di ssociated into flee ions. Thus the equilibrium is consistent with the kinetics of polymerization that indicates a propagation rate constant that is about two orders of magnitude: lower than expected for the PPh 4 enolate ion pair as the sole propagating species. An alternative mec hanistic model involving a PMMA. ylide that propagates directly to giv e either TPP ion pairs or another ylide can not be ruled out at this s tage but it would appear that such a model may be tested with means of polymerization kinetics.