ANIONIC-POLYMERIZATION OF ACRYLIC-MONOMERS .15. LIVING ANIONIC COPOLYMERIZATION OF MIXTURES OF METHYL-METHACRYLATE AND TERT-BUTYL ACRYLATE AS PROMOTED BY DIBENZO-18-CROWN-6

Although mu-coordinating ligands such as LiCl are effective in promoti ng the well-controlled living anionic block copolymerization of methyl methacrylate (MMA) and tert-butyl acrylate (tBuA), whichever monomer is first polymerized, it has been previously shown that a copolymeriza tion of mixtures of these two monomers does not proceed as expected, g iving poor results in terms of both conversion and molecular weight di stribution: that was accounted for by the easy back-biting nucleophili c attack of a highly sensitive methyl ester group by a moderately hind ered PtBuA anion. It is now reported that such a situation can be comp letely modified, when a cation-binding sigma-ligand, i.e., dibenzo-18- CE-6, is used in chelating a sodium counterion and surrounding it with a steric barrier, blocking a large enough space area around the ion p air. In fact, a living copolymerization process of mixtures of MMA and tBuA prevails in THF at -78-degrees-C, in the presence of that Na+/DB -18-CE-6 system. The living copolymer is found, although in a relative ly small extent, to be of a statistical type rather than a blocky one or a mixture of two corresponding homopolymers. Furthermore, using the extended Kelen-Tudos method, the monomer reactivity ratios are determ ined to be r(MMA) = 0.02 and r(tBuA) = 8.81.